Bleeding & Clotting: Step 1 review notes and self-test
Notes for the Bleeding & Clotting rapid review: the clue that separates each of its 6 confusion pairs, with timestamps and a self-test.
October 21, 2026
This video covers the key differences among common bleeding and clotting disorders for USMLE Step 1. Watch the video first, then use these notes to test yourself on the clue that separates each pair.
ITP vs TTP
You separate ITP from TTP by looking for isolated thrombocytopenia versus thrombocytopenia with MAHA and organ injury. ITP has mucocutaneous bleeding and otherwise normal coagulation studies, while TTP has schistocytes and renal or neurologic findings even without the full pentad. Petechiae and mucosal bleeding can occur in both, so you must use the smear and organ findings.
ITP vs TTP ITP is isolated platelets; TTP is thrombocytopenia plus MAHA and organ injury, even without the full pentad. Open the comparison and video →Essential thrombocythemia vs Reactive thrombocytosis
You identify essential thrombocythemia by persistent clonal thrombocytosis with JAK2, CALR, or MPL mutations and large atypical megakaryocytes. Reactive thrombocytosis is a secondary response to infection, inflammation, iron deficiency, malignancy, surgery, trauma, hemolysis, or asplenia. A high platelet count alone does not prove essential thrombocythemia, so you must consider persistence, clonal markers, marrow findings, and a clinical trigger.
Essential thrombocythemia vs Reactive thrombocytosis ET is clonal persistent thrombocytosis with JAK2/CALR/MPL; reactive thrombocytosis is a secondary response to another condition. Open the comparison and video →Hemophilia vs Von Willebrand disease
You separate hemophilia from von Willebrand disease by the bleeding location. Hemophilia causes deep tissue bleeding, hemarthroses, and delayed bleeding after trauma, while von Willebrand disease causes mucosal bleeding from impaired platelet adhesion. Von Willebrand disease can mimic mild hemophilia A with a prolonged PTT because vWF carries and stabilizes factor VIII. If mucocutaneous bleeding occurs with a prolonged PTT, you need vWF antigen, ristocetin cofactor activity, and factor VIII activity because vWF antigen alone can miss qualitative type 2 disease.
Hemophilia vs Von Willebrand disease Hemophilia causes deep bleeding and hemarthroses; vWD causes mucosal bleeding with platelet-adhesion defects. Open the comparison and video →HUS vs TTP and DIC
You separate these disorders by the organ pattern and coagulation studies. HUS emphasizes bloody diarrhea and acute kidney injury, TTP emphasizes neurologic findings with normal PT and PTT, and DIC has prolonged PT and PTT with low fibrinogen. Schistocytes can appear in all three, so you cannot use the smear alone to choose the correct lane.
HUS vs TTP and DIC HUS is diarrhea-kidney MAHA; TTP is neuro MAHA with normal coags; DIC is MAHA plus abnormal coagulation and low fibrinogen. Open the comparison and video →Heparin-induced thrombocytopenia vs DIC
You identify HIT by heparin exposure followed by a platelet fall greater than 50 percent and new thrombosis, usually with normal PT and PTT unless another process is present. DIC causes systemic factor consumption with prolonged PT and PTT, low fibrinogen, high D-dimer, and thrombocytopenia. Both can cause thrombocytopenia and thrombosis, so you must use the heparin timeline, fibrinogen, PT, and PTT.
Heparin-induced thrombocytopenia vs DIC HIT is heparin-timed platelet activation with thrombosis; DIC is systemic factor consumption with abnormal coagulation labs. Open the comparison and video →Inherited thrombophilias vs Antiphospholipid syndrome
You identify inherited thrombophilia by a family pattern of venous thrombosis linked to genetic coagulation defects. You identify antiphospholipid syndrome by acquired autoimmune thrombosis with pregnancy morbidity, livedo reticularis, or antiphospholipid antibodies. Both can cause venous thrombosis, so you must separate family history and genetic or protein activity findings from pregnancy loss and antibody findings.
Inherited thrombophilias vs Antiphospholipid syndrome Inherited thrombophilia is family-pattern venous clotting from genetic coagulation defects; APS is acquired antibody thrombosis with pregnancy loss or antiphospholipid antibodies. Open the comparison and video →Quick self-test
Name the diagnosis from the clue, then tap to check.
Hemolytic uremic syndrome is MAHA, thrombocytopenia, and acute kidney injury, classically after bloody diarrhea from Shiga-like toxin exposure in a child.
HUS · HUS vs TTP and DIC
Thrombocytopenia with MAHA, schistocytes, renal or neurologic findings; fever may occur but the full pentad is uncommon.
TTP · ITP vs TTP
____ causes acquired autoimmune thrombosis with pregnancy morbidity, livedo reticularis, and lupus anticoagulant, anticardiolipin, or anti-beta2 glycoprotein antibodies.
Antiphospholipid syndrome · Inherited thrombophilias vs Antiphospholipid syndrome
____ is clonal platelet overproduction with persistent thrombocytosis, large atypical megakaryocytes, JAK2/CALR/MPL mutations, thrombosis, erythromelalgia, or bleeding from acquired vWF dysfunction.
Essential thrombocythemia · Essential thrombocythemia vs Reactive thrombocytosis
TTP is MAHA plus thrombocytopenia with neurologic findings and normal PT/PTT from ADAMTS13 dysfunction; DIC is systemic coagulation activation with prolonged PT/PTT and low fibrinogen.
TTP and DIC · HUS vs TTP and DIC
____ include Factor V Leiden, prothrombin G20210A, protein C/S deficiency, and antithrombin deficiency, classically causing recurrent or provoked venous thrombosis with family history.
Inherited thrombophilias · Inherited thrombophilias vs Antiphospholipid syndrome
____ is secondary platelet elevation from infection, inflammation, iron deficiency, malignancy, surgery, trauma, hemolysis, or asplenia.
Reactive thrombocytosis · Essential thrombocythemia vs Reactive thrombocytosis
Deep tissue bleeding, hemarthroses, delayed bleeding after trauma, prolonged PTT, and normal platelet count.
Hemophilia · Hemophilia vs Von Willebrand disease
Isolated thrombocytopenia with mucocutaneous bleeding and otherwise normal coagulation studies.
ITP · ITP vs TTP
Systemic coagulation activation from sepsis, trauma, obstetric catastrophe, malignancy, or shock with bleeding, thrombosis, prolonged PT/PTT, low fibrinogen, high D-dimer, and thrombocytopenia.
Mucosal bleeding, epistaxis, menorrhagia, easy bruising, prolonged bleeding time, and sometimes prolonged PTT.
Von Willebrand disease · Hemophilia vs Von Willebrand disease
Keep going
Every pair in this review has a free page in the library with a side-by-side comparison and a practice question. Work through the ones you missed in the self-test first.