A 14-year-old boy with anaemia, jaundice and splenomegaly has spherocytes on smear, a positive osmotic fragility test, and an MCHC of 37 g/dL. Which red cell index abnormality is characteristic of his disorder and virtually unique to it among common anaemias?

• A Elevated MCH due to retained nuclear material
• B Elevated MCHC due to relative dehydration of the red cell ✓
• C Low MCHC due to impaired haemoglobin synthesis
• D Markedly elevated RDW with normal MCHC

Explanation

Hereditary spherocytosis arises from defects in vertical linkages between the membrane skeleton and integral proteins, typically spectrin, ankyrin, band 3 or protein 4.2. Membrane is lost as vesicles while cell volume falls more than haemoglobin content, so the spherocyte becomes dehydrated and the MCHC rises above the normal range of about 31 to 34 g/dL. It is the classic, almost pathognomonic, cause of an elevated MCHC.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

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