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Low HbA1c levels in a poorly controlled diabetic

Q1: What do the data demonstrate?
The data demonstrate inappropriately low HbA1c values in a subject with symptomatic hyperglycaemia (weight loss, osmotic symptoms, and high plasma glucose values) and abundant glycosuria.

Q2: What is the differential diagnosis and what would you do next?
If a laboratory error can be ruled out (repeated samples need to be obtained), the main differential diagnosis is of an abnormal haemoglobin variant. Some causes of abnormal HbA1c values are listed in box 1. The next step is to perform haemoglobin electrophoresis. The following results were obtained in this patient:

Box 1: Causes of high/low HbA1c levels High Newly diagnosed diabetes mellitus. Uncontrolled diabetes mellitus. Non-diabetic hyperglycaemia: acromegaly, phaechromocytoma, thyrotoxicosis, Cushing’s syndrome. Splenectomy. Alcoholism. Low Haemolytic anaemia: congenital (for example, spherocytosis and elliptocytosis), haemoglobinopathies, acquired haemolytic anaemias—for example, drug induced (dapsone, methyldopa). Chronic blood loss. Chronic renal failure (variable).

 

• Alkali/acid elution: haemoglobin A + J (confirms the presence of abnormal haemoglobin J).
  
• Globin: fast beta chain variant (abnormal beta chain).
  
• Isoelectric focusing: haemoglobin A + . . . [Full text of this article]