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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- ITP is isolated thrombocytopenia from immune platelet destruction and impaired platelet production
- CBC shows low platelets with normal hemoglobin and WBC unless bleeding is present
- PT and aPTT are normal; abnormal coagulation studies suggest DIC, liver disease, or another disorder
- Adults often have chronic disease; children often have acute post-viral self-limited ITP
- Treatment depends on bleeding and platelet count: observation, corticosteroids, IVIG, anti-D, rituximab, TPO receptor agonists, or splenectomy
Overview
Immune thrombocytopenia is an acquired autoimmune platelet disorder. Autoantibodies target platelet membrane glycoproteins, leading to splenic clearance and reduced platelet survival. The key diagnostic concept is isolated thrombocytopenia: if anemia, renal injury, neurologic symptoms, schistocytes, or abnormal coagulation studies are present, consider TTP, HUS, DIC, leukemia, or another cause.
Epidemiology
ITP occurs in children and adults. Childhood ITP often follows viral illness and resolves spontaneously. Adult ITP is more often chronic and can be primary or secondary to HIV, hepatitis C, autoimmune disease, lymphoproliferative disorders, or medications.
Clinical Features
Symptoms
Petechiae, purpura, easy bruising
Epistaxis, gingival bleeding, heavy menstrual bleeding
Usually no fever, renal failure, or neurologic symptoms
Severe headache, neurologic symptoms, GI bleeding, or hematuria suggests life-threatening bleeding
Signs
Petechiae on lower extremities or mucosa
Wet purpura or oral hemorrhagic bullae suggest high bleeding risk
No splenomegaly in typical primary ITP; splenomegaly suggests alternative diagnosis
Normal examination apart from bruising/petechiae is common
Investigations
First-line
CBC with smearIsolated thrombocytopenia; smear excludes platelet clumping, schistocytes, blasts
HIV and hepatitis C testingRecommended evaluation for secondary ITP in adults
PT/aPTTNormal in ITP; abnormal values suggest DIC, liver disease, anticoagulant effect, or factor deficiency
Second-line
Pregnancy test when relevantPregnancy changes differential and management
Medication reviewQuinine, TMP-SMX, vancomycin, linezolid, antiepileptics, and many drugs can cause thrombocytopenia
H. pylori testing in selected patientsEradication can improve ITP in some populations
Specialist
Bone marrow biopsyNot routine in typical ITP; consider age >60 with atypical features, additional cytopenias, blasts, or before splenectomy
1
Observation versus treatment
- Observation is reasonable for asymptomatic or minor bleeding with platelets generally >=30,000/µL
- Treat if clinically significant bleeding or lower platelet counts
- Avoid aspirin, NSAIDs, and anticoagulants when possible until bleeding risk is controlled
2
Initial therapy
- Corticosteroids are first-line for non-life-threatening ITP requiring treatment
- IVIG for rapid platelet rise, severe bleeding, perioperative need, or steroid contraindication
- Anti-D immune globulin may be used in selected Rh-positive nonsplenectomized patients
3
Life-threatening bleeding
- Platelet transfusion plus IVIG plus high-dose corticosteroids
- Resuscitate and manage bleeding source; involve hematology urgently
- Platelet transfusions are transient but appropriate for intracranial, GI, or massive bleeding
4
Second-line chronic ITP
- TPO receptor agonists such as eltrombopag, avatrombopag, or romiplostim
- Rituximab or splenectomy in selected patients
Complications
- Intracranial hemorrhage: Rare but feared, especially with very low platelets
- Severe mucosal bleeding: GI, genitourinary, or heavy uterine bleeding
- Chronic relapsing disease: More common in adults
- Treatment complications: Steroid toxicity, infection after splenectomy, thrombosis with TPO receptor agonists
USMLE Step 2 CK Exam Tips
- 1Isolated thrombocytopenia + petechiae + normal PT/aPTT = ITP
- 2Deep tissue bleeding/hemarthrosis suggests coagulation factor deficiency, not platelet disorder
- 3Schistocytes or renal/neuro symptoms = not simple ITP; think TTP/HUS/DIC
- 4Children after viral illness often observed if mild; adults are more often chronic
- 5Life-threatening bleeding in ITP: platelets + IVIG + steroids
- 6Splenomegaly is atypical for primary ITP and should trigger another diagnosis
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