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Of the various lab tests, which is diagnostic of thrombotic thrombocytopenic purpura (TTP)?

a
Elevated LDH
b
Low haptoglobin
c
Elevated CRP
d
Low ADAMTS13 activity
Correct. ADAMTS13 activity < 10% is diagnostic of TTP.
e
Mutation analysis of ADAMTS13

Sort lab test (top) according to whether it is typically altered in TTP or not (bottom):

Elevated AST
Elevated LDH
Increased reticulocytes
Stool positive for Shiga toxin
Low ADAMTS13
Schistocytes on smear
Elevated ALT
Elevated ADAMTS13
Elevated direct bilirubin
Positive DAT
Spur cells in smear
Low haptoglobin
Elevated PT and/or aPTT
Altered in TTP
Not altered in TTP

Abbreviations: TTP, thrombotic thrombocytopenic purpura; LDH, lactate dehydrogenase; DAT, direct antiglobulin test; PT, prothrombin time; aPTT, activated partial thromboplastin time.