What are the steps to diagnose sickle cell disease?

Diagnosing Sickle Cell Disease

The diagnosis of sickle cell disease requires a comprehensive hemoglobinopathy screen using high-performance liquid chromatography, capillary electrophoresis, mass spectrometry, or gel electrophoresis, which should be confirmed by a second test such as solubility testing or electrophoresis on agar in citrate buffer. 1

Primary Diagnostic Methods

• Newborn screening (NBS) is the most common initial diagnostic method in the US, with all 50 states, DC, Puerto Rico, US Virgin Islands, and the US military having screening programs capable of making a definitive diagnosis of SCD at birth 2
• For those without NBS results (e.g., born outside the US), diagnosis requires hemoglobinopathy testing 2
• Hemoglobin electrophoresis is essential to confirm the presence of hemoglobin S and determine the specific genotype (HbSS, HbSC, HbS/β-thalassemia) 1, 3
• A positive sickle solubility test alone is insufficient for diagnosis as it doesn't differentiate between heterozygous (trait), compound heterozygous, or homozygous states 1, 4

Diagnostic Algorithm

1. Initial Screening:

   • Newborn screening where available 2, 1
   • For those without NBS results, perform hemoglobinopathy screen 2

2. Confirmatory Testing:

   • Hemoglobin electrophoresis at alkaline pH or isoelectric focusing 4, 5
   • Cation exchange HPLC (high-performance liquid chromatography) 4
   • Confirmation with a second specific test for HbS such as solubility test or electrophoresis on agar in citrate buffer 4, 5

3. Additional Laboratory Evaluation:

   • Complete blood count to assess for normocytic normochromic anemia 1
   • Reticulocyte count to evaluate bone marrow response to hemolysis 1, 3
   • Markers of hemolysis including bilirubin (total and direct) 1
   • Baseline values for comparison during acute events 1

Genotype Identification

• Four main genotypes should be identified: HbSS, HbSC, and two types of sickle β-thalassemia (Sβ⁰-thalassemia and Sβ⁺-thalassemia) 2
• Rare forms involve coinheritance of HbS with other hemoglobin variants (hemoglobin D-Punjab, E, or O-Arab) 2
• Genotype identification is critical as it impacts disease severity (HbSS and Sβ⁰-thalassemia generally cause more severe disease than HbSC or Sβ⁺-thalassemia) 2

Post-Diagnostic Evaluation

• Establish baseline laboratory values including CBC, reticulocyte count, and pulse oximetry 2
• Document SCD genotype, presence/absence of splenomegaly, and any chronic complications 2
• Refer to a pediatric SCD center or hematologist for comprehensive care comanagement, ideally before 3 months of age 2
• Educate parents about genetic implications for future children and testing of siblings 2

Common Pitfalls to Avoid

• Relying solely on sickle solubility test for diagnosis, which can give false negative results in neonates or heavily transfused patients 1, 4
• Failing to confirm HbS with a second specific test 4, 5
• Not evaluating other factors that modify disease expression (HbF level, alpha-thalassemia status) 4, 5
• Misinterpreting laboratory values without knowing the patient's baseline 1
• Delaying diagnosis and referral to specialized care, which can impact long-term outcomes 2, 6

Special Considerations

• For symptomatic heterozygous patients (sickle cell trait), more sophisticated biochemical tests or molecular biology investigations may be necessary to determine the cause of symptoms 4, 5
• In regions without newborn screening, diagnosis often occurs when patients present with unexplained severe atraumatic pain or normocytic anemia 6
• Genetic counseling should be provided to families after diagnosis of SCD or trait 2