The calculated versus the measured glycosylated haemoglobin (HbA 1c ) levels in patients with type 2 diabetes mellitus

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 (HbA 1c ) is the gold standard for monitoring glycaemic control. Measurements of HbA 1c 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 HbA 1c levels. The equation to compute the calculated HbA 1c also incorporated the fasting blood glucose (FBG) level and was as follows: HbA 1c  = 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 HbA 1c levels ( p  = 0.054). There was a significant correlation between the calculated and measured HbA 1c ( r  = 0.595, p  < 0.001). However, there was no agreement between the calculated and measured HbA 1c . The bias ±SD (limits of agreement) for calculated versus measured HbA 1c was −1.008 ± 2.02% (−5.05, 2.032). Conclusion Despite the presence of a significant correlation between the calculated and measured HbA 1c , the calculated level has shown an unacceptable agreement with the measured HbA 1c .