NBME 22 Answers ↦
yeah, i’ve never heard of antiphospholipids increasing PT time ...
Not sure if that little detail was to throw us off. I think the point of the question was to ID antiphospholipid syndrome based on the clinical criteria (spontaneous abortion + thrombosis)
I actually went down a rabbit hole with this one recently - essentially in vitro findings =/= in vivo findings, clot-wise with anti-phospholipid antibodies.
No mention of lupus anticoagulant, anticardiolipin, or anti Beta 2 antibodies. FA mentios prolonged PTT but nothing on PT. What a piece of shit question. But thanks to the dudes above who explained it
UWorld mentioned "prolong aPTT (and sometimes PT)" in APS
@yb_26 Can u please tell the QID because the one I have seen it says, "Although patients often have prolonged ptt (because the antiphospholipid interferes with ptt test), pt is normal."
just to clarify, lupus anticoag is in antiphospholipid and presents with paradoxical increased ptt +/- pt despite increase risk thrombosis
You should be able to rule it out by the normal Thrombin time. Abnormal fibrinogen would have increased PT/PTT but also increased Thrombin time because the entire pathway is compromised by the inability of fibrinogen to be cleaved to functioning fibrin.
@rainlad Protein C deficiency doesn't cause elevated PT and aPTT. I believe they're both normal and assays for the disease measure protein C activity.
Protein C is an anti-coagulant, so if you lack factor C, then you have MORE clotting factors. This means that the PT and PTT would not be prolonged.