Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (309 page)

   Haptoglobin: decreased.

   Coombs test: negative.

   Hemoglobin: usually normal at birth but decreases sharply during the subsequent 20 days of life.

   Bilirubin is slightly elevated, except in neonatal cases with severe hemolysis, when it may be elevated at birth, resulting in kernicterus if not treated promptly.

   Genetic tests: offered in some research laboratories, usually unnecessary.

   Other Considerations

   Laboratory findings may reflect cholelithiasis or aplastic crises.

   Falsely elevated potassium (hyperkalemia) is due to potassium leaking from RBCs.

HEREDITARY ELLIPTOCYTOSIS (HE)

   Definition

HE is a congenital heterogeneous disorder of the membrane skeleton of RBCs, most commonly a defect in spectrin. It is transmitted in an autosomal dominant mode of inheritance. Occasionally, the transmission is recessive. Individuals who are heterozygous for HE are asymptomatic. Individuals who are homozygous or compound heterozygous (10% of patients) exhibit mild to severe anemia. The disorder is more frequent in African Americans and in patients of Mediterranean origin (previous areas of endemic malaria). Affected neonates may have transient overt hemolytic anemia until adult Hb supervenes.

   Laboratory Findings

   Peripheral blood smear (PBS): more than 50% of RBCs are ellipsoidal or rod shaped. Other markers of hemolysis are uncommon, except in the approximately 10% of severely affected patients. In severe cases of HE, severe poikilocytosis is common.

   Indices: decreased MCV, MCH, MCHC; increased RDW.

   Variant Hb studies and osmotic fragility (see above under HS) are normal.