USMLE Step2 Secrets Hematology
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- What genetic causes of an increased tendency toward clot-forming may appear on the Step 2 exam?
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The list keeps on growing. Watch for factor V Leiden mutation (or activated protein C resistance), prothrombin G20210A multation, or deficiencies in protein C, protein S, or antithrombin III (all autosomal dominant except protein C deficiency) as causes of an increased tendency toward thrombosis.
All are treated with anticoagulant therapy to prevent deep venous thrombosis and pulmonary embolus.
Suspect these conditions if a person under age 35 develops recurrent closts or has no risk factors for clot development. - True or False: The lupus anticoagulant causes a clotting tendency.
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True. Although the lupus anticoagulant may cause a prolonged PTT, the patient has a tendency toward thrombosis.
Look for associated lupus symptoms, positive results on the VDRL or RPR (rapid plasma reagin) tests for syphilis, and/or a history of miscarriages to help you recognize this condition. - Which clotting tests measure which portions of the coagulation cascade? Which medications affect these tests?
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PT (prothrombin time) measures the function of the extrinsin clotting pathway, prolonged by wafarin.
Activated PTT (partial prothrombin time) measures the funciton of the intrinsic clotting pathway, prolonged by heparin.
BT (bleeding time) measures platelet function, prolonged by aspirin. -
Disease: vWF disease
PT
PTT
BT
Platelet Count
RBC Count
Other -
Disease: vWF disease
PT: normal
PTT: high
BT: high
Platelet Count: normal
RBC Count: normal
Other: autosomal dominant (look for family history) -
Disease: Hemophilia A/B
PT
PTT
BT
Platelet Count
RBC Count
Other -
Disease: Hemophilia A/B
PT: normal
PTT: high
BT: normal
Platelet Count: normal
RBC Count: normal
Other: X-linked recessive, A = low factor 8, B = lower factor 9 -
Disease: DIC
PT
PTT
BT
Platelet Count
RBC Count
Other -
Disease: DIC
PT: high
PTT: high
BT: high
Platelet Count: low
RBC Count: normal or low
Other: appropriate history, low level of factor 8 -
Disease: Liver Failure
PT
PTT
BT
Platelet Count
RBC Count
Other -
Disease: Liver Failure
PT: high
PTT: high
BT: normal
Platelet Count: normal/low
RBC Count: normal/low
Other: jaundice, normal factor 8 level; do not give vitamin K (ineffective); use FFP -
Use of heparin
PT
PTT
BT
Platelet Count
RBC Count
Other -
Use of heparin
PT: normal
PTT: high
BT: normal
Platelet Count: normal or low
RBC Count: normal
Other: watch for thrombocytopenia and thrombosis -
Use of warfarin
PT
PTT
BT
Platelet Count
RBC Count
Other -
Use of warfarin
PT: high
PTT: normal
BT: normal
Platelet Count: normal
RBC Count: normal
Other: vit K antagonist (vit K helps make factors 2, 7, 9, 10) -
Disease: ITP (idiopathic thrombocytopenic purpura)
PT
PTT
BT
Platelet Count
RBC Count
Other -
Disease: ITP
PT: normal
PTT: normal
BT: high
Platelet Count: low
RBC Count: normal
Other: watch for preceding URI, antiplatelet antibodies and increased megakaryocytes -
Disease: TTP (thrombotic thrombocytopenic purpura)
PT
PTT
BT
Platelet Count
RBC Count
Other -
Disease: TTP
PT: normal
PTT: normal
BT: high
Platelet Count: low
RBC Count: LOW
Other: hemolysis (smear shows schistocytes), CNS symptoms, treat with plasmapheresis; do not give platelets -
Disease: Scurvy
PT
PTT
BT
Platelet Count
RBC Count
Other -
Disease: Scurvy
PT: normal
PTT: normal
BT: normal
Platelet Count: normal
RBC Count: normal
Other: fingernail and gum hemorrhages, bone hemorrhages, caused by vitamin C deficiency