What are the American Diabetes Association (ADA) criteria to diagnose diabetes?

ADA Criteria to Diagnose Diabetes

The American Diabetes Association recognizes four distinct methods to diagnose diabetes: A1C ≥6.5%, fasting plasma glucose ≥126 mg/dL, 2-hour plasma glucose ≥200 mg/dL during oral glucose tolerance test, or random plasma glucose ≥200 mg/dL with classic hyperglycemic symptoms. 1, 2

The Four Diagnostic Pathways

1. Hemoglobin A1C ≥6.5% (48 mmol/mol)

• Must be performed in a laboratory using an NGSP-certified method standardized to the DCCT assay 1, 2, 3
• Point-of-care A1C assays should NOT be used for diagnosis due to lack of standardization 2, 3
• Offers greater convenience (no fasting required), better preanalytical stability, and less day-to-day variation during stress or illness 1

2. Fasting Plasma Glucose ≥126 mg/dL (7.0 mmol/L)

• Fasting defined as no caloric intake for at least 8 hours 1, 2
• Blood should be drawn in the morning and processed within 15-30 minutes to prevent glycolysis 4
• Use a tube with a rapidly effective glycolytic inhibitor 4

3. 2-Hour Plasma Glucose ≥200 mg/dL (11.1 mmol/L) During OGTT

• Performed using a 75-g anhydrous glucose load dissolved in water 1, 2, 3
• For children, use 1.75 g/kg up to maximum of 75 g 1
• Patient should consume at least 150 g carbohydrates daily for 3 days before testing 3

4. Random Plasma Glucose ≥200 mg/dL (11.1 mmol/L)

• Only valid when accompanied by classic symptoms of hyperglycemia 1, 2
• Classic symptoms include polyuria, polydipsia, weight loss, polyphagia, fatigue, and blurred vision 1
• This is the ONLY criterion that does not require confirmatory testing if symptoms are present 5

Critical Confirmation Requirements

In the absence of unequivocal hyperglycemia (hyperglycemic crisis with clear symptoms), any abnormal test result MUST be confirmed by repeat testing on a separate day. 1, 2, 4

Three Options for Confirmation:

1. Repeat the same test on a different day 2, 4
2. Use a different diagnostic test 2
3. Measure two different tests on the same day 3

When Confirmation is NOT Required:

• Patient presents with hyperglycemic crisis AND random glucose ≥200 mg/dL 1, 5
• Patient has classic symptoms AND random glucose ≥200 mg/dL 5

Important Caveats and Pitfalls

A1C Testing Limitations:

Do NOT use A1C for diagnosis in these conditions: 2, 3

• Hemoglobinopathies (sickle cell trait, thalassemia) 1
• Conditions with abnormal red cell turnover: pregnancy (second/third trimester), recent blood loss or transfusion, erythropoietin therapy, hemolysis 1, 2
• For patients with sickle cell trait, use an A1C assay without interference from abnormal hemoglobins 1
• In these situations, use only blood glucose criteria for diagnosis 1

Handling Discordant Results:

• If one test meets diabetes criteria but another doesn't (e.g., A1C 6.3% but fasting glucose 7.4 mmol/L), repeat the abnormal test within 3-6 months 4
• Factors causing discordance include preanalytical variability, recent acute illness, racial/ethnic differences in A1C, and conditions affecting red cell lifespan 4
• The patient should be considered to have diabetes only after repeat testing confirms the diagnosis 4

Special Population Considerations:

• Children with type 1 diabetes presenting with classic symptoms require immediate diagnosis and treatment—delays must be avoided 1
• Stress hyperglycemia in young children with acute illness does not necessarily indicate diabetes 1
• For gestational diabetes, different criteria apply at 24-28 weeks gestation 2

Prediabetes Categories (Increased Risk)

The ADA defines prediabetes as: 2, 3

• A1C 5.7-6.4% (39-47 mmol/mol), OR
• Fasting glucose 100-125 mg/dL (5.6-6.9 mmol/L), OR
• 2-hour OGTT 140-199 mg/dL (7.8-11.0 mmol/L)

Patients meeting prediabetes criteria should receive counseling on weight loss and exercise to prevent progression to diabetes. 2