The SST (also called "sickle cell screen " �) was developed as a rapid screening for the presence of HbS. Red cells are lysed, and the released Hb is reduced by sodium hydrosulfite.
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 patients 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 � �-globulins
Polycythemia vera
Increased number of Heinz bodies (e.g., postsplenectomy)
Increased number of nucleated RBCs
Some rare Hb variants, such as HbC Harlem or C Georgetown