Which laboratory finding is characteristic of ITP?

• A. Prolonged PT and aPTT
• B. Isolated thrombocytopenia with normal coagulation tests
• C. Elevated D-dimer
• D. Anemia with low MCV

Answer: (B)

ITP causes immune-mediated destruction of platelets, so the main lab clue is a low platelet count with normal clotting function. The coagulation tests (PT and aPTT) stay normal because the issue lies with platelets, not with the coagulation factors. This pattern helps distinguish it from conditions like DIC or liver disease, where clotting times are prolonged and indicators like D-dimer are elevated. Anemia with a low MCV points to a separate red blood cell issue, not the platelet problem seen in ITP. So the hallmark finding is isolated thrombocytopenia with normal coagulation tests. If you looked at a smear, you’d often see low platelets, sometimes with larger platelets, but clotting tests would be normal.