Hematology & Coagulation Flashcards

A patient has a prolonged PT and a normal aPTT. Which single factor deficiency best explains this?

Answer: Factor VII

Factor VII is the only factor measured by the PT alone and not by the aPTT.

A preoperative patient has a markedly prolonged aPTT, a normal PT, and no bleeding history. The most likely cause is:

Answer: Factor XII deficiency

Factor XII deficiency prolongs the aPTT in vitro but does not cause clinical bleeding.

A prolonged aPTT does NOT correct after a 1:1 mix with normal pooled plasma. This indicates:

Answer: A circulating inhibitor

Normal plasma supplies enough of any missing factor, so failure to correct points to an inhibitor such as lupus anticoagulant or a factor antibody.

A patient with a hematocrit of 65% needs coagulation testing. How should the sodium citrate collection be adjusted?

Answer: Decrease the citrate volume

A high hematocrit means less plasma, so the citrate must be reduced to keep the correct anticoagulant-to-plasma ratio.

Which test is preferred for monitoring low-molecular-weight heparin therapy?

Answer: Anti-Xa assay

LMWH acts mainly against factor Xa and has little effect on the aPTT, so it is monitored with a heparin-calibrated anti-Xa assay.

A patient with delayed bleeding and poor wound healing has a normal PT, aPTT, and platelet count, but the clot dissolves in 5 M urea. Which factor is deficient?

Answer: Factor XIII

Factor XIII cross-links fibrin; without it, clots are soluble in 5 M urea while routine screening tests stay normal.

An elevated D-dimer specifically indicates:

Answer: Plasmin degradation of cross-linked fibrin

D-dimer is formed only when plasmin breaks down fibrin that has been cross-linked by factor XIIIa.