Sickle Solubility Test (SST)

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Subject: Sickle Solubility Test (SST)

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Definition

  • 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 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

    • Increased number of Heinz bodies (e.g., postsplenectomy)

    • Increased number of nucleated RBCs

    • Some rare Hb variants, such as HbC Harlem or C Georgetown

 
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