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

Workup for Immune Thrombocytopenic Purpura (ITP)

ITP is a diagnosis of exclusion requiring isolated thrombocytopenia with a normal peripheral blood smear (except for reduced platelets) and absence of other obvious causes—the workup focuses on excluding alternative diagnoses rather than confirming ITP through specific testing. 1, 2

Essential Initial Workup

History and Physical Examination

• Assess bleeding symptoms: Document presence and severity of petechiae, bruising, mucosal bleeding (epistaxis, gingival bleeding, menorrhagia), gastrointestinal hemorrhage, or hematuria 1
• Medication review: Identify all drugs that could cause thrombocytopenia, as this is critical for excluding drug-induced causes 2
• Exclude secondary causes: Look specifically for splenomegaly, hepatomegaly, or lymphadenopathy—their presence suggests secondary ITP or alternative diagnoses 2
• Infection history: Document recent viral illnesses, as secondary ITP can be associated with viral infections 1

Required Laboratory Tests

Complete Blood Count (CBC) with Peripheral Smear:

• Must show isolated thrombocytopenia without anemia or leukopenia 2
• Peripheral smear should demonstrate normal or slightly larger platelets with no schistocytes 2
• Critical step: Exclude pseudothrombocytopenia (EDTA-dependent platelet agglutination) by reviewing the smear 2

Infectious Disease Screening (Adults):

• HIV testing 2
• Hepatitis C virus (HCV) testing 2
• Helicobacter pylori testing 2

Tests NOT Routinely Required

Bone marrow examination is generally unnecessary in the following situations:

• Children and adolescents with typical ITP features 1
• Patients prior to initiating IVIg therapy 1, 2
• Typical presentations in adults with isolated thrombocytopenia and normal peripheral smear 1

However, bone marrow biopsy should be considered when:

• Atypical features are present (anemia, leukopenia, abnormal peripheral smear) 1
• Patient fails to respond to first-line therapy 1
• Prior to splenectomy 1
• Atypical presentations such as low immature platelet fraction (IPF) that suggest hypoproliferative thrombocytopenia 3

Antiplatelet antibody testing:

• Has no value in routine diagnosis of ITP 4
• Should not be ordered as it does not change management 4

Additional Workup to Exclude Alternative Diagnoses

When thrombotic thrombocytopenic purpura (TTP) is in the differential:

• Coagulation studies: PT, aPTT, fibrinogen, D-dimer to exclude DIC 2
• ADAMTS13 activity level if microangiopathic hemolytic anemia is present 5
• Lactate dehydrogenase (LDH) and indirect bilirubin to assess for hemolysis 5

Pregnancy-specific considerations:

• The workup is essentially the same as non-pregnant patients 4
• Additionally exclude: gestational thrombocytopenia, preeclampsia, HELLP syndrome, DIC, folate deficiency, acute fatty liver, antiphospholipid antibody syndrome 4

Diagnostic Criteria Summary

ITP diagnosis requires ALL of the following:

• Isolated thrombocytopenia (typically platelet count <100 × 10⁹/L) 1, 2
• Normal peripheral blood smear except for reduced platelets 2
• No splenomegaly, hepatomegaly, or lymphadenopathy on physical exam 2
• Negative workup for secondary causes 1, 2

Common Pitfalls to Avoid

• Do not delay treatment waiting for bone marrow results in typical presentations with severe bleeding or very low platelet counts (<10-20 × 10⁹/L) 1, 2
• Do not transfuse platelets in ITP without life-threatening bleeding—platelet transfusions are contraindicated as they are rapidly destroyed and provide no benefit 2
• Do not base treatment decisions on platelet count alone—bleeding symptoms and bleeding risk are more important than the absolute platelet number 2
• Do not assume elevated IPF confirms ITP—atypical cases with low IPF exist and may require bone marrow examination to exclude hypoproliferative causes 3