Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (310 page)

   Other Considerations

   Some degree of elliptocytosis may be seen in peripheral blood smear (PBS) of other types of anemia.

HEREDITARY PYROPOIKILOCYTOSIS (HP)

   Definition

HP is considered a subtype of HE. In homozygous individuals, it results in a severe congenital hemolytic anemia. It occurs primarily in people of African ancestry.

   Laboratory Findings

Peripheral blood smear (PBS): RBCs are markedly misshapen (fragments, microspherocytes, elliptocytes, pyknotic forms). The RBCs
fragment
when heated at 45–46°C (normal RBCs show budding and fragmentation only when heated at 49°C). Severe microcytosis and micropoikilocytosis are present.

HEREDITARY OVALOCYTOSIS (HO)

   Definition

HO is a condition of altered membrane deformability. It is very common in Southeast Asia, where its prevalence is 5–25% in malaria endemic areas. Transmission is autosomal dominant, but so far only heterozygous individuals have been identified. Most affected people express minimal hemolysis.

   Laboratory Findings

Peripheral blood smear (PBS): oval-shaped RBCs with one or two transverse ridges or a longitudinal slit.

   Other Considerations

Hereditary ovalocytosis can be confused with hereditary elliptocytosis.

HEREDITARY STOMATOCYTOSIS

   Definition

Hereditary stomatocytosis is an uncommon autosomal dominant disease resulting from defective RBC permeability to sodium and potassium ions.

   Laboratory Findings

Peripheral blood smear (PBS):

   Homozygous individuals: >35% of RBCs show slit-like areas of central pallor, producing a mouth-like appearance.

   Heterozygous individuals: 1–25% stomatocytes.

   Anemia: similar to that of hereditary ovalocytosis.

   Homozygous individuals: varying degrees of hemolysis.