What is the HbA1c (Hemoglobin A1c) threshold for diagnosing diabetes?

From the Guidelines

The HbA1c threshold for diagnosing diabetes is 6.5% or higher, as recommended by the most recent guidelines and research 1. This means that if a person's HbA1c test result is 6.5% or above, they would be diagnosed with diabetes. For confirmation, the test should be repeated unless there are clear symptoms of diabetes present. The HbA1c test measures the average blood glucose levels over the previous 2-3 months by showing the percentage of hemoglobin proteins in the blood that are glycated (have glucose attached). This test is preferred for diagnosis because it doesn't require fasting and provides a longer-term picture of glucose control than a single blood glucose reading. Some key points to consider include:

• Prediabetes is typically defined as an HbA1c between 5.7% and 6.4%, while normal levels are below 5.7% 1.
• The 6.5% threshold was established because research shows that this is the level at which the risk for diabetic retinopathy and other complications significantly increases 1.
• After diagnosis, treatment targets are typically set lower, often aiming for HbA1c levels below 7% for most adults with diabetes to reduce the risk of complications 1.
• It's also important to note that certain conditions, such as hemoglobin variants or chronic kidney disease, may affect HbA1c measurement, and point-of-care assays should not be used for diagnosis 1.
• The HbA1c test should be performed in a laboratory using a method that is NGSP certified and standardized to the DCCT assay 1.
• If the initial HbA1c value is 6.5% to 6.9%, a new diagnosis of diabetes should be based on a confirmatory fasting blood glucose level of at least 7.0 mmol/L (≥126 mg/dL) 1.
• Sequential HbA1c values that are within 0.5% do not statistically differ from one another unless the assay coefficient of variation is less than 3%, and ideally less than 2% 1.
• Treatment decisions based solely on a single HbA1c measurement without consideration of other clinical data, such as glucose monitoring results, may lead to unnecessary initiation or intensification of therapy 1.
• Comparing HbA1c tests performed in different clinical laboratories introduces another source of error, as does use of point-of-care HbA1c testing, which is not subject to systematic quality oversight 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule out laboratory error, unless the diagnosis is clear on clinical grounds, such as a patient with classic symptoms of hyperglycemia or hyperglycemic crisis 1.
• The healthcare professional might opt to follow the patient closely and repeat the testing in 3–6 months if the results are near the margins of the threshold for a diagnosis 1.
• The current diagnostic criteria for diabetes are summarized in various guidelines, including those from the ADA and the WHO 1.
• The International Expert Committee and the ADA have recommended that HbA1c can be used for screening for diabetes 1.
• The frequency of HbA1c testing for diagnosis has not been established, but guidelines similar to those for glucose-based testing seem appropriate 1.
• HbA1c assays are not recommended for screening for or diagnosis of gestational diabetes mellitus 1.
• The established glucose criteria for the diagnosis of diabetes remain valid, including the FPG and 2-h PG 1.
• Patients with severe hyperglycemia, such as those who present with severe classic hyperglycemic symptoms or hyperglycemic crisis, can continue to be diagnosed when a random (or casual) plasma glucose of $200 mg/dL (11.1 mmol/L) is found 1.
• It is likely that in such cases the health care professional would prefer that a test result diagnostic of diabetes should be repeated to rule

From the Research

HbA1c Threshold for Diagnosing Diabetes

• The International Expert Committee recommends a diagnosis of diabetes if the HbA1c level is greater than or equal to 6.5% and confirmed with a repeat HbA1c test 2.
• A diagnostic cut-off point of HbA1c greater than or equal to 6.5% may miss a substantial number of people with type 2 diabetes, including some with fasting hyperglycemia, and misses most people with impaired glucose tolerance 2.
• The use of HbA1c as a primary diagnostic test will reduce diabetes prevalence, and it suggests that HbA1c and OGTT measurements cannot simply be exchanged, but most probably detect and define different categories of diabetes 3.

Optimal Cut-off Value

• A study found that a level of 6.1% (43 mmol/mol) is optimal for diagnosing diabetes, with a sensitivity of 80% and 75% and a specificity of 77% and 78% respectively 4.
• The American Diabetes Association included HbA1c ≥6.5% into the revised criteria for the diagnosis of diabetes, but the debate as to whether HbA1c should be used to diagnose diabetes is far from being settled 5.

Limitations of HbA1c Testing

• HbA1c testing has the potential for systematic error, and factors that may not be clinically evident can impact HbA1c test results and may systematically raise or lower the value relative to the true level of glycemia 2.
• The sensitivity of HbA1c for diagnosing diabetes is low, indicating that more than half of diabetic subjects are missed when using this test 3.