Low HbA1c Despite Marked Hyperglycemia: Importance of Fructosamine in a Diabetic Patient with Anemia

Abstract

Glycated haemoglobin (HbA1c) is the most widely used biomarker for assessing long-term glycaemic control in patients with diabetes mellitus; however, its reliability may be compromised in conditions affecting red blood cell lifespan, leading to discordance between HbA1c and plasma glucose levels. We report the case of a 57-year-old female with diabetes mellitus who consistently had markedly elevated fasting blood sugar (261 mg/dL) and postprandial blood sugar (336 mg/dL), despite a normal HbA1c value of 5.4%. Haematological evaluation revealed anaemia with an RBC count of 3.61 million/µL, haemoglobin of 9.12 g/dL and packed cell volume (PCV) of 27.8%, suggesting that the HbA1c result may have been falsely low because of altered erythrocyte survival. Review of previous laboratory records demonstrated a similar pattern of recurrent low HbA1c values despite persistent hyperglycaemia. To further evaluate glycaemic status, fructosamine testing was performed and revealed a markedly elevated concentration of 346.39 µmol/L, confirming poor short-term glycaemic control. This case highlights the limitations of HbA1c as the sole indicator of glycaemic status in patients with anaemia and emphasises the importance of correlating HbA1c with plasma glucose measurements and haematological parameters. Fructosamine was a valuable alternative biomarker because it reflected recent glycaemic control independently of red blood cell lifespan. Awareness of such discrepancies is essential to prevent misinterpretation of glycaemic status and support appropriate clinical decisions.