Very low HbA1C, is it a problem?

An important problem to manage diabetes mellitus is controlling the patients` blood glucose. Fluctuation of blood glucose results in molecular biochemistry change and can result in unwanted diabetic complications (1). In clinical practice, hemoglobin A1C (HbA1C) is a common useful laboratory test to follow-up patients with diabetes (2). Sometimes, an unexpected laboratory result can be observed. Here, the authors presented a case of extremely low hemoglobin A1C level and discussed its clinical importance. The current study was a consultation case of an abnormally low HbA1C level. The patient was a 40-year-old male with the history of cerebral stroke and on control of diabetes mellitus. The patient was firstly diagnosed with diabetes mellitus at the time of diagnosis of stroke. The HbA1C level of this patient at the first time on the first diagnosis of diabetes mellitus was 7.2% (fasting plasma glucose 218 mg/ dL). This case was on strict diet control and took oral metformin 2000 mg/day. The HbA1C levels at the 1st, 2nd, 3rd, 4th, 5th, and 6th months after the first diagnosis were 6.4%, 6.4%, 6.1%, 6.1%, 5.9%, and 5.9%, respectively. However, the aberrant result was observed on the 7th month that the HbA1C was 3.2% (the fasting blood glucose level at this time was 92 mg/dL). The laboratory already checked and validated the result. The other laboratory investigations including complete blood count, blood lipid, uric acid, liver function test, and renal function test were within normal limit. Focusing on the performance of HbA1C test, the precision and accuracy of the test, coefficient of variation (CV) was 1.2% and mean bias +0.4 %, which were according to the clinical pathology standards (3). All tests were performed at an ISO15189 certified laboratory. Therefore, the main question is “What is the cause of abnormally low HbA1C in this case?”