Diagnosing Idiopathic Thrombocytopenic Purpura (ITP)

To diagnose immune thrombocytopenia, your doctor will try to exclude other possible causes of bleeding and a low platelet count, such as an underlying illness or medications you or your child may be taking.

Blood tests can check the levels of platelets. Rarely, adults might need a bone marrow exam to rule out other problems.

Source: https://www.mayoclinic.org/diseases-conditions/idiopathic-thrombocytopenic-purpura/diagnosis-treatment/drc-20352330#:~:text=To%20diagnose%20immune%20thrombocytopenia%2C%20your,check%20the%20levels%20of%20platelets.