HbA1c vs Fasting Plasma Glucose for Prediabetes, Diabetes Diagnosis

Patients with undiagnosed diabetes screened via fasting plasma glucose (FPG) may remain undiagnosed vs patients screened via hemoglobin A1c (HbA1c) blood test, according to a study published in PLOS ONE.

Researchers collected overnight fasting blood samples from 3523 individuals (2356 women) in Ho Chi Minh City, Vietnam. Diabetes was diagnosed with an HbA1c value ≥6.5% or an FPG level ≥7 mmol/l. Prediabetes was diagnosed with HbA1c levels between 5.7% and 6.4% or FPG levels between 5.6 and 6.9 mmol/L.

Both diabetes and prediabetes were diagnosed in 9.7% and 34.6% (95%CI, 8.7%-10.7% and 33%-36.2%), respectively, in patients diagnosed via the HbA1c test. Patients diagnosed with diabetes and prediabetes via the FPG test were 6.3% and 12.1% (95%CI, 5.5%-7.2% and 11.1%-13.2%). Only 59% of patients diagnosed with diabetes based on HbA1c criteria were also diagnosed based on FPG criteria.

The investigators concluded that HbA1c testing has a higher sensitivity for identifying patients at risk for diabetes vs FPG, and therefore may have a greater impact on the diagnoses, cost, burden, and treatment of patients with diabetes. Discordance was found between HbA1c and FPG in patients identified as diabetic and prediabetic, but not between patients identified as diabetic and prediabetic compared with patients within the normal range group.

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Study Limitations

Participants were all of Asian (Vietnamese) descent and from a highly urban population, thereby limiting the generalizability of results globally.


Ho-Pham LT, Nguyen UDT, Tran TX, Nguyen TV.  Discordance in the diagnosis of diabetes: comparison between HbA1c and fasting plasma [published online August 17, 2017]. PLOS ONE. doi:10.1371/journal.pone.0182192