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Qualitative determination of presence of hemoglobin S; detect sickling hemoglobins; evaluate hemolytic anemia, undiagnosed hereditary anemia with morphologic (sickle-like) abnormalities on peripheral blood smear.
False-positive solubility test for sickling may be due to polycythemic blood; interference by some forms of hyperglobulinemia; and a variety of abnormal hemoglobins, including I, Bart, CGeorgetown, Alexandra, CHarlem, Porto Alegre, Memphis/S, CZiguinchor, and STravis.1 Positive tests should be confirmed by hemoglobin fractionation. A positive reaction also occurs in the presence of many Heinz bodies (eg, after splenectomy), and in blood protein disorders due to precipitation of plasma proteins. False-negative solubility test reactions may occur with inadequate quantities of blood from anemic patients (hemoglobin levels <8.0 g/dL); high concentration of Hb F or of phenothiazines may inhibit the sickle reaction;1 quantities of hemoglobin S too small to detect, as at birth or with transfusions of nonhemoglobin S into patients with hemoglobin S. The appearance of hemoglobin S is genetically delayed and is not present in sufficient quantity until after three months of age. Maximum levels are not reached until about six months of age. Solubility tests are unlikely to be reliably positive until after six months of age; therefore, this test should not be used for testing neonates or children younger than six months of age.
Distinction between Hb S β-thalassemia and sickle cell anemia is not always possible on clinical, hematologic, or electrophoretic grounds. Thalassemia heterozygotes have hypochromia and microcytosis, but overlap values exist. Differentiation can best be made by family or molecular pathology methods. Regional prevalence in the midwest area of Hb S β-thalassemia is estimated to be 1:23,000 of the black population. It is recommended that positive sickle cell patients be further evaluated with Hb fractionation (HPLC), Hb F studies, and family studies. Complete characterization may require sophisticated laboratory studies with DNA amplification.2
1. Miale JB. Laboratory Medicine: Hematology. 6th ed. St Louis, Mo: Mosby-Year Book Inc; 1982:624-625.
2. Chehab FF, Kan YW. Detection of sickle cell anaemia mutation by colour DNA amplification. Lancet. 1990 Jan 6; 335(8680):15-17. PubMed 1967329
