What is the best next laboratory test for a 7-year-old boy with jaundice, anemia, splenomegaly, and a family history of similar symptoms, with laboratory results showing elevated reticulocytes, indirect hyperbilirubinemia, and a peripheral smear with anisocytosis, spherocytes, and polychromatophilia?

From the Guidelines

The best next step in evaluation of this patient is B. Eosin-5-maleimide binding, as it is a diagnostic test for hereditary spherocytosis, a condition characterized by hemolytic anemia, which is suggested by the patient's clinical presentation and laboratory findings, including anemia, reticulocytosis, indirect hyperbilirubinemia, and a peripheral smear showing spherocytes, anisocytosis, and polychromatophilia 1.

Key Points to Consider

• The patient's symptoms, such as jaundice, fatigue, and pallor, along with a family history of similar symptoms, are consistent with hereditary spherocytosis.
• Laboratory findings, including anemia (hemoglobin 10 g/dL), reticulocytosis (10%), and indirect hyperbilirubinemia (total bilirubin 3 mg/dL with direct bilirubin only 0.2 mg/dL), support this diagnosis.
• The peripheral smear showing spherocytes, anisocytosis, and polychromatophilia is also characteristic of hereditary spherocytosis.
• Hereditary spherocytosis is an inherited red blood cell membrane disorder that leads to increased red cell destruction in the spleen, causing hemolytic anemia.
• The eosin-5-maleimide binding test measures the amount of band 3 protein in the red cell membrane, which is typically reduced in hereditary spherocytosis, and has high sensitivity and specificity for diagnosing this condition 1.

Rationale for Choosing Eosin-5-maleimide Binding Test

• The test is specific for diagnosing hereditary spherocytosis, which is the most likely diagnosis based on the patient's clinical presentation and laboratory findings.
• Other options, such as bone marrow evaluation, erythrocyte CD55 and CD59 protein testing, glucose-6-phosphate dehydrogenase activity, hemoglobin electrophoresis, serum B12 level, and serum iron level, are not as directly relevant to diagnosing hereditary spherocytosis.
• The eosin-5-maleimide binding test is a non-invasive and relatively simple test that can provide a definitive diagnosis, allowing for appropriate management options to be considered, such as splenectomy 1.

From the Research

Diagnosis of Hereditary Spherocytosis

The patient's symptoms, such as pale conjunctivae, scleral icterus, and generalized jaundice, along with laboratory results, suggest a diagnosis of hereditary spherocytosis (HS). The presence of spherocytes on the peripheral smear and a negative direct and indirect antiglobulin (Coombs) test support this diagnosis.

Laboratory Tests for HS

Several laboratory tests can be used to diagnose HS, including:

• Eosin-5-maleimide binding test (EMA) 2, 3, 4, 5, 6
• Flow cytometric osmotic fragility test (FOFT) 2, 5
• Cryohemolysis test 5
• Hemoglobin (Hb)/mean corpuscular hemoglobin concentration (MCHC) ratio 5

Best Next Step in Evaluation

Based on the evidence, the best next step in evaluation of this patient would be to perform an EMA binding test, as it has been shown to be a sensitive and specific test for diagnosing HS 2, 3, 4, 5, 6. This test can help confirm the diagnosis of HS and distinguish it from other causes of hemolytic anemia.

Key Findings

Key findings that support the use of EMA binding test include:

• High sensitivity and specificity of EMA binding test in diagnosing HS 2, 3, 5
• Ability of EMA binding test to distinguish HS from other causes of hemolytic anemia 4, 5
• Correlation of EMA binding test results with clinical severity of HS 5
• Effective use of EMA binding test in diagnosing HS in neonates 6