SAT-552 - Can Hemoglobin A1c Be Used as A Reliable Indicator for Diabetes Mellitus?

Case Presentation
Case 1
A 39-yr-old Asian female with recently diagnosed hypertension presented to the endocrine clinic for initial evaluation and management for HbA1c levels of 7.3-7.4% (Nl=4-5.6) with a 3 lb. weight loss, but denied polyuria or polydipsia, and family history of DM, Fructosamine was elevated at 295 umol/L (Nl 205-285). A 75-gram glucose tolerance test showed baseline = 115 mg/dL, 1 hr= 275 mg/dL, and 2 hr=237 mg/dL. Autoantibodies for type 1 DM were negative (GAD 65 < 5 IU/mL, (Nl < 5 IU/mL), Zinc transporter < 10 U/mL (Nl < 15), Islet cell, Insulin autoantibody < 0.4 U/mL (Nl < 0.4). Thyroid antibodies were also negative.

Case 2
An 19-yr-old Latino male presented to the endocrine clinic for evaluation and
management of prediabetes (HbA1c= 6.1%). He was started on Metformin 500 mg daily and increased to 1000 mg daily but had stopped taking Metformin. Family history= grandparents with DM. Fructosamine was normal at 232 umol/L (Nl=205-285). Autoantibodies for type 1 DM were negative. A 75-gram glucose tolerance test showed baseline glucose =100 mg/dL, 1 hour=185 mg/dL and 2 hours=159 mg/dL, thus confirming the diagnosis of prediabetes.

Case 3
A 41-yr old African American male, 9 years post bariatric surgery, was referred for HbA1c of 11.7%. Although both parents had DM, he denied a prior history and symptoms of hyperglycemia. Fructosamine was elevated; 352 mMol/L (Nl=205-285), C-peptide 1.19 ng/mL (NL=0.5-2) with blood glucose of 98 mg/dL. Autoantibodies were negative. There were no hemoglobinopathies. Baseline CGM (14 days) showed GMI=6.1%. Lab HbA1C=7.6%.

Conclusion
Our cases confirm that reliance on HbA1c alone as the sole assessment of glycemia may not always be adequate and multiple measures of glycemia are required to ensure reliability and accuracy for clinical decision making, since discordance exists between HbA1c and other measures of glycemic control from various factors (hemoglobinopathies, iron deficiency, B12 , folate deficiency anemias, asplenia, severe hypertriglyceridemia, severe hyperbilirubinemia, uremia, medications, lead poisoning, chronic alcohol, salicylates and opioids). Racial differences may also lead to variation, with higher HbA1c in certain African American and other ethnicities. Our cases highlight that it is important to understand these potential sources of discordance to improve diabetes care.

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