Glycated hemoglobin in diagnosis of diabetes mellitus and pre-diabetes; validation by oral glucose tolerance test. The Tromsø OGTT Study.

BACKGROUND

Glycated hemoglobin (HbA(1c)) 6.5% has recently been recommended by the World Health Organization (WHO) and the American Diabetes Association (ADA) as an alternative diagnostic criterion for diabetes mellitus (DM).

AIM

To evaluate HbA(1c) as an alternative to oral glucose tolerance test (OGTT) for diagnosis of DM and pre-diabetes and to find the optimal HbA(1c) cut-off points for DM and pre-diabetes in our population.

SUBJECTS AND METHODS

The subjects were recruited from the Tromsø Study, performed for the 6th time in 2007-2008 with 12,984 participants. All subjects with HbA(1c) in the range 5.8-6.9% and a random sample of subjects with levels 5.3-5.7% were invited to an OGTT.

RESULTS

Among 3476 subjects who completed the OGTT, 199 were diagnosed with DM. The best sensitivity (69.8%) and specificity (81.8%) were found at HbA(1c) 6.2%. For HbA(1c) 6.5% we found a sensitivity of 34.7% and specificity 97.1%. The best cut-off points for impaired fasting glucose (no.=314) and impaired glucose tolerance (no.=404) were found at HbA(1c) 5.9% and 6.0%, respectively. Pre-diabetes detected only by OGTT was associated with worse metabolic characteristics than pre-diabetes detected only by HbA(1c).

CONCLUSIONS

The optimum HbA(1c) cutoff point for DM in our population was lower than that proposed by WHO and ADA. To establish more precisely the HbA(1c) levels predictive of micro- and macro-vascular complications, long-term prospective studies are needed. Population- specific optimum cut-off points may be necessary.