What is the diagnostic workup for pediatric Immune Thrombocytopenic Purpura (ITP)?

Diagnostic Workup for Pediatric ITP

The diagnostic workup for pediatric ITP requires only a complete blood count (CBC), peripheral blood smear examination, and HIV/HCV testing—bone marrow examination is unnecessary in children with typical features. 1

Essential Initial Testing

Complete Blood Count and Peripheral Smear

• A CBC with platelet count is the fundamental first test, showing isolated thrombocytopenia (platelet count <100 × 10⁹/L) without anemia or leukopenia. 1, 2
• Peripheral blood smear examination by a qualified hematologist is paramount and must demonstrate: 1
  • Thrombocytopenia with normal-sized or slightly larger platelets (not giant platelets approaching RBC size)
  • Normal red blood cell morphology (no schistocytes or poikilocytosis)
  • Normal white blood cell morphology (though atypical lymphocytes and eosinophilia may occur in children with ITP) 1
• The smear must exclude pseudothrombocytopenia from EDTA-dependent platelet agglutination. 1, 2

Viral Testing

• HIV and HCV testing should be performed routinely in all children with suspected ITP, regardless of risk factors, as these infections can be clinically indistinguishable from primary ITP. 1, 2

What NOT to Do

Bone Marrow Examination

• Bone marrow examination is NOT necessary in children and adolescents with typical ITP features (isolated thrombocytopenia, normal CBC otherwise, appropriate clinical presentation). 1
• Bone marrow is NOT required even before initiating corticosteroids, IVIg therapy, or splenectomy in typical cases. 1, 2
• A 1996 study found that among 127 consecutive children with suspected ITP who underwent bone marrow aspiration, other causes were identified in only 4% of children—all of whom had atypical presenting features. 1

Antibody Testing

• Antinuclear antibody (ANA) testing is NOT necessary in the routine evaluation of children with suspected ITP. 1
• Antiplatelet antibody assays are NOT recommended as they lack specificity and sensitivity. 1
• Antiphospholipid antibodies, direct antiglobulin testing, and platelet antigen-specific antibodies are of uncertain utility and not routinely indicated at initial presentation. 1

Clinical Features That Must Be Present

History and Physical Examination

• The child should be otherwise healthy with sudden onset of bruising and petechiae, often 1-4 weeks after a viral illness. 3, 4
• Physical examination should show NO lymphadenopathy, NO hepatosplenomegaly (mild splenomegaly may occur in 12% of children, especially infants, but moderate/massive splenomegaly suggests alternative diagnosis). 1
• NO fever, bone/joint pain, skeletal abnormalities, non-petechial rash, or constitutional symptoms should be present—these are red flags requiring additional workup. 1

Red Flags Requiring Additional Testing

If ANY of the following atypical features are present, additional testing including bone marrow examination is warranted: 1

• Abnormal hemoglobin level or white blood cell count
• Abnormal white cell morphology on smear
• Schistocytes or significant red blood cell abnormalities
• Family history of thrombocytopenia or bleeding disorders
• Hepatosplenomegaly or lymphadenopathy
• Fever or constitutional symptoms
• Skeletal or soft-tissue morphologic abnormalities

Optional Testing in Specific Scenarios

• Helicobacter pylori testing is NOT routinely recommended in children except in high-prevalence geographic areas. 1
• Blood group Rh(D) typing should be performed if anti-D immunoglobulin treatment is being considered. 1
• Immunoglobulin levels to screen for common variable immune deficiency may be considered, as ITP can be a presenting feature in 17/21 patients with CVID in one series, though routine screening utility is unclear. 1

Common Pitfalls to Avoid

• Do not delay diagnosis waiting for antiplatelet antibody results—these tests are neither sensitive nor specific enough to guide clinical decision-making. 1
• Do not perform bone marrow examination reflexively—this represents a major change from older 1996 guidelines and reduces unnecessary invasive procedures. 1
• Do not miss pseudothrombocytopenia—always review the peripheral smear personally to confirm true thrombocytopenia. 1, 2
• Do not assume ITP without excluding HIV/HCV—these can present identically and require different management. 1