Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (302 page)

   Homozygous condition: There is no HbA1, and HbC forms the majority variant Hb; HgF is slightly increased. Peripheral blood smear (PBS) shows a variable number of target cells (≤40%), a variable number of microspherocytes, occasionally nucleated RBCs, and a few tetragonal crystals within RBCs.

HEMOGLOBIN C–β-THALASSEMIA

HbC-β-thalassemia is a form of β-thalassemia (see below). Affected individuals are commonly asymptomatic, although moderate hemolysis may be present. These individuals have a moderate microcytic, hypochromic, hemolytic anemia, and splenomegaly. Their red cells may show Hb C crystals.

HEMOGLOBIN D DISEASE

   Definition

Autosomal inherited hemoglobinopathy prevalent in Southeast Asia and in parts of India (HbD Punjab). The heterozygous form is asymptomatic with no anemia.

   Laboratory Findings

   Hb variant analysis demonstrates the abnormal Hb at acid pH (it has the same mobility as HbS at alkaline pH). There are no other laboratory abnormalities in the
heterozygous
individual.

   RBC: mild hemolytic, microcytic anemia in
homozygous
individuals; their peripheral blood smear (PBS) shows target cells and spherocytes.

HEMOGLOBIN E DISEASE

   Definition

The most common structural hemoglobinopathy in the United States after HbS and HbC. Autosomal inherited hemoglobinopathy, prevalent in Southeast Asia (15–30% of the population in Cambodia, Thailand, parts of China, Burma, and Vietnam). Heterozygous individuals have similar findings as patients with β-thalassemia trait (see below). Homozygotes exhibit more microcytosis but are asymptomatic.

   Laboratory Findings

   Hb variant analysis shows 95−97% HbE in the homozygous (the rest is HbF); 30−35% in individuals carrying HbE trait. Electrophoretic mobility is the same as for HbA2, but it is present in much higher concentrations. It separates from HbC and O on citrate agar electrophoresis at acid pH.

   CBC.

   Mild hemolytic, microcytic (MCV 55−70 fL) anemia or no anemia in the homozygous.

   Erythrocytosis may be present (RBC approximately 5,500/μL) in both the trait and in the homozygous.

   Peripheral blood smear (PBS) shows 25–60% target cells and microcytes in the homozygous individuals.