ITP Workup
The workup for ITP requires a complete blood count, peripheral blood smear evaluation by a qualified hematologist/pathologist, and selective testing to exclude secondary causes based on patient age and clinical presentation.
Essential Initial Testing
Complete Blood Count
- ITP is characterized by isolated thrombocytopenia (platelet count <100 × 10⁹/L) with otherwise normal CBC 1, 2
- If anemia is present, it should be proportional to bleeding duration and may indicate iron deficiency 1
- Check reticulocyte count if anemia exists to distinguish production vs. destruction 1
Peripheral Blood Smear (Mandatory)
This is paramount to diagnosis and must be reviewed by a qualified hematologist or pathologist 1. The smear should show:
- Small numbers of large platelets with normal morphology
- Absence of schistocytes (which would suggest TTP-HUS)
- No leukocyte inclusion bodies (which would indicate MYH9-related disease)
- Rule out EDTA-dependent platelet agglutination causing pseudothrombocytopenia 1, 3
Age-Stratified Additional Testing
For All Adults
- HIV and HCV serologic testing - mandatory regardless of risk factors or local prevalence, as these infections are clinically indistinguishable from primary ITP and may occur years before other symptoms 1
- H. pylori testing (preferably urea breath test or stool antigen test, not serology) - should be considered where it may have clinical impact 1
- Blood group Rh(D) typing if anti-D immunoglobulin therapy is being considered 1
For Patients >60 Years Old
Bone marrow examination (both aspirate and biopsy) with flow cytometry and cytogenetic testing - particularly helpful for identifying CLL-associated ITP 1
For Patients with Red Flags
Bone marrow examination is indicated if any of the following are present 1:
- Systemic symptoms (fever, weight loss)
- Hepatomegaly or lymphadenopathy
- Moderate to massive splenomegaly (mild splenomegaly may be normal in younger patients)
- Abnormal findings on peripheral smear beyond isolated thrombocytopenia
- Consideration of splenectomy
Tests NOT Routinely Recommended
Limited Clinical Utility
- Antiplatelet antibody assays - not recommended routinely as platelet-associated IgG is elevated in both immune and non-immune thrombocytopenia 1
- Antiphospholipid antibodies - found in ~40% of ITP patients but don't affect treatment response; only test if symptoms of antiphospholipid syndrome present 1
- Antinuclear antibodies - may predict chronicity in childhood ITP but not routinely indicated 1
Consider in Specific Contexts
- Thyroid function testing and antithyroid antibodies - 8-14% of ITP patients develop clinical hyperthyroidism longitudinally; mild thrombocytopenia can occur with thyroid dysfunction 1
Common Pitfalls to Avoid
- Do not skip the peripheral smear review - automated counts miss critical morphologic abnormalities
- Do not assume low-risk patients don't need HIV/HCV testing - these should be universal in adults 1
- Do not use serologic H. pylori testing after recent IVIG - produces false positives 1
- Do not order extensive autoimmune panels without clinical indication - ITP remains a diagnosis of exclusion based on clinical assessment 2, 4