Low Positive Predictive Value of Hemoglobin A1c for Diagnosis of Prediabetes in Clinical Practice



      Positive predictive value (PPV) of hemoglobin A1c (HbA1c) for diagnosis of prediabetes in clinical practice has not been well studied.


      In a prospective study, patients diagnosed with prediabetes based on HbA1c (5.7%-6.4%) underwent a 75-g oral glucose tolerance test (oGTT) as the gold standard test to diagnose dysglycemia. Demographics, anthropometrics, comorbidity, concomitant prescription medications and biochemical data were collected.


      We identified 66 patients with HbA1c-based prediabetes with a mean HbA1c of 6.00 ± 0.20%. However, based on the OGTT, 32 had normal glucose tolerance (NGT), 26 had prediabetes and 8 had diabetes yielding a PPV of HbA1c of 39.4%. In univariate analysis, the patients with the OGTT-based prediabetes administered more medications for associated medical problems compared with the NGT group (5.9 ± 2.2 versus 2.6 ± 1.8, P < 0.0001). After adjustment for baseline variables, the medication use remained significantly different between OGTT-based prediabetes and NGT groups (P = 0.041).


      PPV of HbA1c for diagnosis of prediabetes in clinical setting is low. Patients with HbA1c of 5.7% to 6.4% should undergo OGTT to confirm diagnosis of dysglycemia.

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