The calculated versus the measured glycosylated haemoglobin (HbA1c) levels in patients with type 2 diabetes mellitus

Abstract

Background: Diabetes mellitus (DM) is a chronic metabolic disorder that is increasing globally. It is associated with chronic complications that are more common among patients with poor glycaemic control. Glycosylated haemoglobin (HbA1c) is the gold standard for monitoring glycaemic control. Measurements of HbA1c are relatively expensive and not available in some remote areas of developing countries. Methods: We conducted a cross-sectional study to evaluate the agreement between the calculated and measured HbA1c levels. The equation to compute the calculated HbA1c also incorporated the fasting blood glucose (FBG) level and was as follows: HbA1c = 2.6 + 0.03 × FBG (mg/dl). Result: We enrolled 290 patients with type 2 DM in this study. Of these, 204 (70.3%) were females and the mean (SD) age was 54.9 (12.8) years. The mean (SD) diabetes duration was 6.8 (5.5) years. There were 211 (72.8%) patients using oral hypoglycaemic agents, 62 (21.4%) were using insulin and 17 (5.9%) were using both insulin and oral hypoglycaemic agents. There was a borderline difference between the mean (SD) calculated and measured HbA1c levels (p = 0.054). There was a significant correlation between the calculated and measured HbA1c (r = 0.595, p < 0.001). However, there was no agreement between the calculated and measured HbA1c. The bias ±SD (limits of agreement) for calculated versus measured HbA1c was −1.008 ± 2.02% (−5.05, 2.032). Conclusion: Despite the presence of a significant correlation between the calculated and measured HbA1c, the calculated level has shown an unacceptable agreement with the measured HbA1c.