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sickle screen; hemoglobin solubility

Also see HemoTypeSC Indications: - screening for - sickle cell trait & - sickle cell disease - other hemoglobin S genetic variants Principle: - sodium dithionite is added to lysed erythrocytes to reduce hemoglobin - the solution becomes turbid when hemoglobin S is present - with other hemoglobins, the solution remains clear Reduced Hgb S is insoluble in concentrated phosphate buffers. Under the same conditions, Hgb A, as well as most other hemoglobins, is soluble. RBC's are lysed by a surfactant & the released hemoglobin reduced by sodium hydrosulfite (NaHSO3) in concentrated phosphate buffer. The released Hgb S when reduced in the phosphate buffer forms a turbid suspension which is easily visualized. Hgb A, as well as most other hemoglobins, remain soluble under these conditions. Both sickle cell disease & sickle cell trait yield a positive result. Severe anemia can cause false negatives. Therefore, if the Hgb is < 8 g/dL, the sample volume for testing should be doubled. Elevated levels of Hgb F may result in false negatives. Thus specimens from infants < 6 months of age do not yield reliable results. Some rare hemoglobin variants, such as Hgb C Harlem, or C Georgetown may also give a positive sickle screen. Blood from patients with multiple myeloma, cryoglobulinemia, & other dysglobulinemias, may give false positives. This problem can be eleviated by saline washing the patient's red cells. Clinical significance: - useful for screening - does not detect - carriers of hemoglobin C - beta-thalassema - does not distinguish between sickle cell trait & sickle cell disease or other hemoglobin S genetic variants (hemoglobin SC) Interferences: 1) false positives - lipemic specimens - abnormal gamma-globulins - polycythemia - increased numbers of Heinz bodies (post-splenectomy) - increased numbers of nucleated erythrocytes 2) false negatives - blood hemoglobin < 7 g/dL - phenothiazines - high hemoglobin F (thus unreliable for newborns) - low % of hemoglobin S

Related

hemoglobin S HemoTypeSC sickle cell (hemoglobin SS) disease sickle cell trait; hemoglobin S trait

General

clinical hematology test turbidometry

References

  1. Interpretation of Diagnostic tests, 8th edition, Wallach J, Lippincott, Williams & Wilkens, Philadelphia, 2007
  2. Hemoglobin S, Evaluation (Sickle Cell) Laboratory Test Directory ARUP: 50520
  3. Panel of 10 tests Laboratory Test Directory ARUP: 50610
  4. Panel of 10 tests Laboratory Test Directory ARUP: 2005792