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NBME 22 Answers

nbme22/Block 3/Question#16 (39.6 difficulty score)
A 27-year-old woman comes to the physician ...
Antiphospholipid antibodiesπŸ”,πŸ“Ί
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 +11 
submitted by hayayah(1081),
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Pganryecn + Hx fo sismroboth &--t;g ithnk ppplihtdionshioa rmnesydo

eTh TP dna PTT are dgnerlopo /td fetcrneierne rfom eht eabtoisdin to hilsohppidsp.o ohTrbnim etim .rmloan

Hda ot ifnd eahescrr ertcials utabo it so teak it fmro eher dan odnt' twaes your ..emi.t

monoloco  yeah, i’ve never heard of antiphospholipids increasing PT time ... +22  
goldenwakosu  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) +4  
johnthurtjr  I actually went down a rabbit hole with this one recently - essentially in vitro findings =/= in vivo findings, clot-wise with anti-phospholipid antibodies. +3  
link981  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 +8  
yb_26  UWorld mentioned "prolong aPTT (and sometimes PT)" in APS +3  
oslerweberrendu  @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." QID: 1298 +  
kevin  just to clarify, lupus anticoag is in antiphospholipid and presents with paradoxical increased ptt +/- pt despite increase risk thrombosis +1  



 +0 
submitted by amphotericin(8),
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owh duwol yuo elur tuo )C bafedngiioinm?rsey I frsit sdsugee APS ubt ehtwcdis it escaeub of the T/TPTP tginh

suckitnbme  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. +6  



 -1 
submitted by rainlad(23),

How do you rule out Protein C deficiency in this case? doesn't that also increase risk of thrombosis and miscarriage?

suckitnbme  @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. +4  
drzed  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. +3