Haemoglobin A1C Levels Constantly Below Lower Reference Limi
Haemoglobin A1C values lower than the normal range most likely do not mean too good a control of blood sugar in diabetic patients. Careful investigation to find the underlying causes is mandatory to provide well-qualified medical care.
Various hemoglobinopathies with chronic hemolysis should be considered as the background reason, especially in an endemic area for thalassemia.

Haemoglobin HbA1C (A1C) levels have been widely recognized as being a reliable estimate of long-term blood sugar levels, particularly in evaluating the efficacy of glycaemic control in diabetic patients. Nevertheless, abnormally increased or decreased A1C levels may be detected due to various underlying pathologic causes, chiefly including altered erythropoiesis rates, erythrocyte destruction, haemoglobinopathy, alcoholism, chronic renal failure, splenomegaly, hyperbilirubinaemia, hypertriglyceridaemia and certain drugs.

This is a case involving an elderly diabetic patient with moderately severe microcytic anaemia and persistently low A1C levels which had been initially misunderstood as representing over-strict glycaemic control. Disclosing the underlying cause of abnormally decreased A1C levels may act as a reminder to the physician in charge of the necessity of using alternative tests other than A1C measurement in guiding diabetic management.

In conclusion, physicians must be aware of the potential interference from haemoglobinopathies with enhanced erythrocyte destruction in A1C measurement among individuals from an endemic area for thalassaemia.

Source: https://www.ejcrim.com/index.php/EJCRIM/article/view/1338/1851