Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1220 page)

   Use

   Patients with sickle cell trait are asymptomatic and do not present with sickle cells on the peripheral blood smear. The definitive diagnosis is made by hemoglobin variant studies. Reduced HbS is insoluble and forms a turbid suspension in the SST.

   HbA and most other hemoglobins are soluble under these conditions. Both sickle cell anemia (homozygous) and the sickle cell trait can be detected with this procedure.

   Limitations

   Recent transfusions may cause false-positive and false-negative results.

   False-negative results may occur with:

   The patient’s Hb <7 g/dL

   Phenothiazine drugs

   Unreliable for newborn screening because of high HbF and low percentage of HbS in the 1st year of life

   False-positive results may occur with

   Increased turbidity (e.g., lipemic specimens)

   Abnormal β-globulins

   Polycythemia vera