Laboratory Testing for Sickle Cell Disease and Trait
Hemoglobin electrophoresis is the gold standard confirmatory test for diagnosing sickle cell disease or trait, and should be ordered directly as the initial test for anyone without documented newborn screening results. 1, 2
Primary Diagnostic Test
Hemoglobin electrophoresis separates and identifies different hemoglobin types (HbA, HbS, HbC, HbF) and definitively distinguishes between sickle cell trait (HbAS: 55-65% HbA, 30-40% HbS) and sickle cell disease variants (HbSS, HbSC, HbS-β⁰-thalassemia). 1, 2 This single test provides comprehensive hemoglobin phenotype information and should be the first-line diagnostic approach for individuals born outside the U.S., immigrants, or anyone born before 1987 when universal newborn screening became routine. 1
Supporting Laboratory Tests
When sickle cell disease is suspected or confirmed, order these additional tests:
- Complete blood count (CBC) to identify normocytic anemia, elevated white blood cell counts, and establish baseline hemoglobin levels 2
- Reticulocyte count to assess bone marrow response and degree of hemolysis 2
- Peripheral blood smear to visualize sickled red blood cells (though this is supportive, not diagnostic)
In acute presentations, additional markers may include:
- Lactate dehydrogenase, bilirubin, and aspartate aminotransferase which are elevated during hemolysis and vaso-occlusive crises 2
Alternative Testing Methods
High-performance liquid chromatography (HPLC) is an alternative to electrophoresis with high sensitivity and specificity, commonly used in newborn screening programs with 99.5-100% accuracy. 1, 3 HPLC provides rapid automated quantification of hemoglobin fractions and can detect HbS levels as low as 1-2%. 4, 5
Critical Pitfalls to Avoid
Never rely solely on solubility testing for definitive diagnosis. 1 Solubility tests (like the sickle cell prep) cannot differentiate between sickle cell trait (HbAS) and sickle cell disease (HbSS, HbSC), making them inadequate as standalone diagnostic tools. 6 While they may be used for initial screening (such as in NCAA athlete screening), they must always be followed by confirmatory hemoglobin electrophoresis or HPLC. 1
Always confirm the diagnosis with a second, more specific test. 6 The diagnosis of HbS should never be accepted based on a single electrophoretic test alone—confirmation with either a solubility test, electrophoresis on agar in citrate buffer, or HPLC is essential. 6
Do not assume negative newborn screening in individuals born before 1987 or outside the U.S. 1 Universal newborn screening only became routine in 1987, so older patients and immigrants require direct testing regardless of reported history. 1
Special Considerations for Pregnancy
When sickle cell trait is identified in a pregnant woman, the baby's father must also be tested to determine fetal risk. 1 If both parents have sickle cell trait, there is a 25% chance of having a child with sickle cell disease. 1 This partner testing is essential for appropriate prenatal counseling and potential prenatal diagnosis options. 7
Newborn Screening Context
All 50 U.S. states, the District of Columbia, Puerto Rico, the U.S. Virgin Islands, and the U.S. military perform universal newborn screening for hemoglobinopathies that can definitively diagnose sickle cell trait at birth. 1 Results should be documented in the medical record and discussed with families at diagnosis, school entry, preadolescence, and transition to adult care. 1
Genotype Confirmation Importance
Confirming the specific genotype (HbSS, HbSC, HbS-β⁰-thalassemia, or HbS-β⁺-thalassemia) is crucial because it determines disease severity and treatment intensity. 8 Children with HbSS and HbS-β⁰-thalassemia are more severely affected than those with HbSC or HbS-β⁺-thalassemia. 8
Diabetes Monitoring Caveat
For individuals with sickle cell trait requiring diabetes screening or monitoring, use an A1C assay without interference from hemoglobin variants, as sickle cell trait lowers A1C values by approximately 0.3% compared to individuals without the trait at the same glycemic level. 1