Sickle Screen

From Anvita Health Wiki

Contents 1 Indications 2 Principle 3 Clinical-significance 4 Interferences 5 More General Terms 6 Additional Terms 7 References

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

• false positives

• lipemic specimens
• abnormal gamma-globulins
• polycythemia
• increased numbers of Heinz bodies (post- splenectomy)
• increased numbers of nucleated erythrocytes

• false negatives

• blood hemoglobin < 7 g/ dL
• phenothiazines
• high hemoglobin F (thus unreliable for newborns)
• low % of hemoglobin S

More General Terms

• clinical hematology test
• turbidometry

Additional Terms

• hemoglobin S
• sickle cell (hemoglobin SS) disease
• sickle cell trait

References

Interpretation of Diagnostic tests, 8th edition, Wallach J, Lippincott, Williams & Wilkens, Philadelphia, 2007

sickle screen