What is the summarized screening test for Diabetes Mellitus (DM)?

From the Guidelines

The most effective screening test for diabetes is the hemoglobin A1C test, with a threshold of 6.5% or higher indicating diabetes, as it is widely standardized and does not require fasting 1.

Screening Tests for Diabetes

The following tests are used to detect high blood sugar levels before symptoms appear:

• Fasting plasma glucose (FPG) test: measures blood sugar after an overnight fast, with values of 126 mg/dL or higher indicating diabetes
• Hemoglobin A1C test: reflects average blood glucose over the past 2-3 months, with 6.5% or higher suggesting diabetes
• Oral glucose tolerance test (OGTT): measures how the body processes glucose, with readings of 200 mg/dL or higher at the two-hour mark indicating diabetes
• Random plasma glucose tests: can be used when symptoms are present, with values of 200 mg/dL or higher plus symptoms suggesting diabetes

Recommendations for Screening

Screening is recommended for:

• Adults aged 45 and older
• Those with risk factors like obesity or family history
• During pregnancy to detect gestational diabetes Early detection through these screening tests is crucial because diabetes can damage blood vessels and nerves silently for years before symptoms appear, and early intervention with lifestyle changes or medication can prevent or delay complications like heart disease, kidney damage, and vision problems 1.

Key Considerations

• The A1C test is now widely standardized in the United States and is a valuable tool for screening and diagnosis of diabetes 1.
• The FPG test and OGTT are also suitable tests for diabetes, but the FPG test is preferred in clinical settings because it is easier and faster to perform, more convenient and acceptable to patients, and less expensive 1.

From the Research

Summary of Screening Tests in Diabetes

• The key dysglycemia screening tests for diabetes are fasting plasma glucose and hemoglobin A1C 2.
• Hemoglobin A1C (HbA1c) is a useful screening and diagnostic test for diabetes because it does not require patients to be fasting, reflects longer-term glycemia, and has well-standardized laboratory methods 3.
• The American Diabetes Association and US Preventive Services Task Force recommend opportunistic 3-yearly screening for diabetes using HbA1c and fasting plasma glucose 2.

Diagnostic Criteria for Diabetes

• HbA1c of 6.5% or greater, confirmed by a plasma glucose-specific test, is recommended for the diagnosis of diabetes 3.
• Fasting plasma glucose of 126 mg/dL or greater, or 2-hour plasma glucose of 200 mg/dL or greater, are also used for the diagnosis of diabetes 3, 4.
• The optimal cut point of HbA1c for detecting diabetes is 6.1%, which has a sensitivity and specificity of 81.0% and 81.0%, respectively 5.

Comparison of Screening Tests

• HbA1c has a lower sensitivity for detecting diabetes compared to fasting plasma glucose and 2-hour plasma glucose 4.
• The combined use of fasting plasma glucose and HbA1c may be a more sensitive and specific screening tool for identifying high-risk individuals with diabetes and impaired glucose tolerance 5.
• HbA1c can guide, but cannot replace, oral glucose tolerance tests for the diagnosis of diabetes 6.

Recommendations for Screening

• Screening standards should be established to prompt further testing and closer follow-up, including fasting plasma glucose of 100 mg/dL or greater, random plasma glucose of 130 mg/dL or greater, or HbA1c greater than 6.0% 2, 3.
• The simultaneous measurement of fasting plasma glucose and HbA1c may be a useful screening strategy for identifying high-risk individuals with diabetes and impaired glucose tolerance 5, 6.