Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (300 page)

HEMOGLOBIN S–HEMOGLOBIN C DISEASE

   Definition

A moderately severe sickling disease, clinically intermediate between sickle cell anemia and sickle cell trait. Occurs in 1 of 833 people of African ancestry.

   Laboratory Findings

   Hb electrophoresis: HbA is absent; HbS and HbC are present in approximately equal amounts. HbF is ≤6%.

   CBC.

   Anemia: mild to moderate normochromic, normocytic.

   Peripheral blood smear (PBS): tetragonal crystals within the RBC in 70% of patients. Target cells and plump/angulated sickle cells, rather than typical sickle cells, are identified.

   MCV is low, or low normal; MCHC is high.

SICKLE CELL–α-THALASSEMIA DISEASE

α-Thalassemia modifies the severity of sickle cell anemia. Otherwise, it is usually clinically insignificant.

SICKLE CELL–β-THALASSEMIA DISEASE

   Definition

Condition of mild to moderate severity found in 1 of every 1,667 people of African ancestry.

   Laboratory Findings

   Hb electrophoresis: HbS varies between 20% and 90%; HbF between 2% and 20%. If the HbS is very high and HbA1 is suppressed, the disease is severe. In milder cases, HbA1 is 25–50%. HbA2 is increased (due to the presence of β-thalassemia), but it has to be differentiated from HbC, which has a similar migration pattern.

   CBC

   RBC: hypochromic, microcytic anemia with decreased MCV (iron deficiency must be ruled out).

   Peripheral blood smear (PBS): target cells are prominent; other findings resemble those of sickle cell anemia.