[Which are the significance of low level of glycated hemoglobin A1c?]

Glycated hemoglobin A1c (HbA1c) reflects the mean blood glucose over the lifespan of red blood cells and has become a valuable tool both for diagnosis and monitoring of diabetes. Nevertheless, some factors may under-estimate the HbA1c value, compromising its application. The aim of this retrospective study was to evaluate the incidence rate of HbA1c lower than 4% and to identify some clinical and biological factors that can potentially reduce the HbA1c level. Between January 1st 2015 and October 1st 2017, we selected 17 patients with a HbA1c level lower than 4% that were measured in our laboratory of biochemistry at the university medical center of Caen. From the medical records, we identified medical conditions, treatments and biological parameters that could potentially explain a decrease of HbA1c level. Meanwhile the measurement of HbA1c, 8/16 patients had hemoglobin level lower than 100 g/L and 5/6 presented with reticulocytosis (>100 G/L). Ten patients over 17 suffered from hepatopathy (cirrhosis from various etiologies) with abnormal liver blood tests for 12 patients. Two patients showed hemolytic anemia and another one was investigated for hypoglycemia due to congenital hyperinsulinism. Finally, 3 patients were treated with drugs known to lower HbA1c levels. True hypoglycemia periods but also other circumstances which are known to alter erythrocytes lifespan or the glycation process may decrease HbA1c level. Such biological result should be critically interpreted and alternative biological markers should be considered.