What are the recommended tests for diagnosing sickle cell disease?

Recommended Tests for Diagnosing Sickle Cell Disease

The diagnosis of sickle cell disease requires a full hemoglobinopathy screen using high performance liquid chromatography (HPLC), capillary electrophoresis, mass spectrometry, or gel electrophoresis, with confirmation by a second test such as a sickle solubility test or electrophoresis on agar in citrate buffer. 1

Primary Diagnostic Tests

Initial Screening Tests

• Hemoglobinopathy screen - The primary diagnostic test that identifies the presence and percentages of different hemoglobin types

  • Methods include:
    • High performance liquid chromatography (HPLC)
    • Capillary electrophoresis
    • Mass spectrometry
    • Gel electrophoresis

• Confirmatory test - A second test must always be performed to confirm the presence of HbS 2

  • Options include:
    • Sickle solubility test
    • Electrophoresis on agar in citrate buffer
    • Isoelectrofocusing (provides better resolution than conventional electrophoresis)

Important Considerations for Testing

• A single sickle solubility test should never be used in isolation as it:

  • Cannot differentiate between heterozygous (trait), compound heterozygous, or homozygous (disease) states
  • May give false negative results in neonates or heavily transfused patients 1
  • Only detects the presence of HbS but not other hemoglobin variants 3

• Hospital laboratories typically follow an algorithm:

  1. Either perform a rapid sickle solubility test first, then proceed to full hemoglobinopathy screen if positive
  2. Or perform the full hemoglobinopathy screen directly 1

Additional Testing for Disease Characterization

Once sickle cell disease is diagnosed, additional tests are recommended to characterize the disease and assess for complications:

• Complete blood count (CBC) - To assess baseline hemoglobin level and identify elevated white blood cell counts that may indicate underlying complications 1

• Hemoglobin electrophoresis with quantification - To determine exact percentages of HbS, HbF, HbA, and other hemoglobin variants 2

• Reticulocyte count - Important for monitoring disease activity and evaluating anemia 1

• Genetic testing - For beta-globin gene variants and alpha-globin gene number (to identify concurrent alpha-thalassemia) 4

Screening Recommendations

• All patients at risk of hemoglobinopathy should be screened before surgery, unless they are:

  • Of solely northern or eastern European, Jewish, or South-East Asian heritage
  • Have been screened previously with documented results 1

• For newborns, screening is performed as part of national newborn screening programs in many countries 1

• Point-of-care tests like HemoTypeSC may be used in resource-limited settings with high sensitivity (99.5%) and specificity (99.9%) 5

Common Pitfalls to Avoid

1. Relying on a single test - Always confirm HbS with a second test using a different methodology 2

2. Misinterpreting results in transfused patients - Recent transfusions can alter hemoglobin percentages and lead to false negative results 1

3. Testing during acute illness - Interpretation may be complicated during vaso-occlusive crises or other acute events

4. Failing to distinguish trait from disease - Proper quantification and identification of all hemoglobin variants is essential to differentiate sickle cell trait from various forms of sickle cell disease 3

5. Overlooking other hemoglobinopathies - Tests should be able to detect other relevant hemoglobin variants (HbC, HbD, etc.) that may interact with HbS 2

By following these comprehensive testing protocols, accurate diagnosis of sickle cell disease can be achieved, allowing for appropriate management and genetic counseling.