Type of test Blood
Normal findings
No sickle cells present or no Hgb S identified
Test explanation and related physiology
Both sickle cell disease (homozygous for Hgb S) and sickle cell trait (heterozygous for Hgb S) can be detected by this screening study. Sickle cell anemia results from a genetic homozygous defect and is caused by the presence of Hgb S instead of Hgb A. When Hgb S becomes deoxygenated, it tends to bend in a way that causes the red blood cell (RBC) to assume a sickle shape. Hgb S is found in varying quantities in 8% to 10% of the black population.
The Sickledex test is only a screening test. The definitive diagnosis of sickle cell disease or trait is made by Hgb electrophoresis in which Hgb S can be identified and quantified.
Interfering factors
• Any blood transfusions within 3 to 4 months before the sickle cell test may cause false-negative results because the donor’s normal hemoglobin may dilute the recipient’s Hgb S.
• Polycythemia or paraproteinemias may cause false-positive solubility results.
• Infants younger than 3 months may have false-negative results.
* Phenothiazines may cause false-negative results.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: lavender
• If the test is positive, further testing is done.
* Inform patients with sickle cell anemia that they should avoid situations in which hypoxia may occur.
Abnormal findings
- Sickle cell trait
- Sickle cell anemia
