What is the initial blood workup for suspected idiopathic thrombocytopenia purpura (ITP)?

Initial Blood Workup for Idiopathic Thrombocytopenia Purpura (ITP)

The diagnosis of ITP requires only a history, physical examination, complete blood count (CBC), and examination of the peripheral blood smear to exclude other causes of thrombocytopenia. 1, 2

Essential Diagnostic Tests

• Complete blood count (CBC) with platelet count is the fundamental first test for suspected ITP 3
• Peripheral blood smear examination is essential to confirm thrombocytopenia and exclude other causes 1
• On peripheral smear, look for:
  • Thrombocytopenia with normal-sized or slightly larger platelets (but not giant platelets) 1
  • Normal red blood cell morphology (absence of schistocytes, poikilocytosis) 1
  • Normal white blood cell morphology (absence of immature or abnormal cells) 1

What NOT to Include in Routine Initial Workup

• Bone marrow aspiration is generally not indicated in the routine initial workup of patients with suspected ITP 1, 2

  • Exception: Bone marrow examination should be performed in patients with persistent thrombocytopenia (lasting more than 6-12 months) or those unresponsive to initial therapy 1

• The following tests are generally unnecessary for initial diagnosis when history, physical exam, and blood counts are compatible with ITP 1:

  • Antinuclear antibody (ANA)
  • Direct antiglobulin test
  • HIV testing (unless risk factors present)
  • Platelet antigen-specific antibody
  • Mean platelet volume
  • Reticulocyte count
  • Urinalysis

Special Circumstances Requiring Additional Testing

• HIV antibody testing should be performed in patients with risk factors for HIV infection 1
• Abdominal CT scan or ultrasound examination is appropriate only in patients with suspected splenomegaly on physical examination 1
• In pregnant women, blood pressure measurement and liver function tests should be performed to rule out preeclampsia 1

Clinical Pearls and Pitfalls

• ITP is a diagnosis of exclusion - there is no single diagnostic test that confirms ITP 4, 5
• The peripheral smear should show decreased platelets with normal morphology of other cell lines 1, 5
• The presence of schistocytes, poikilocytosis, or abnormal white blood cells suggests alternative diagnoses 1
• Platelet counts <20,000-30,000/μL significantly increase bleeding risk and may require treatment 4
• Bone marrow examination is not necessary before initiating IVIg therapy 1

Management Considerations Based on Initial Workup

• Patients with platelet counts >30,000 and minimal symptoms generally do not require specific treatment 3
• Treatment is indicated for patients with platelet counts <20,000 with significant mucous membrane bleeding or <10,000 with minor purpura 1, 3
• For severe, life-threatening bleeding, hospitalization with high-dose parenteral glucocorticoids, IVIg, and platelet transfusions may be necessary 3, 5

Remember that the diagnosis of ITP is primarily clinical, supported by laboratory findings, and requires the exclusion of other causes of thrombocytopenia. The initial workup should be focused and avoid unnecessary testing when the clinical presentation is typical.