A prolonged aPTT result is obtained on a patient diagnosed with acute disseminated intravascular coagulation (DIC). The most likely cause of the prolonged aPTT is

• A. In addition to DIC, the patient is deficient in a factor required for the extrinsic pathway.
• B. DIC is characterized by synthesis of less stable coagulation factors, which deteriorate rapidly in the circulation.
• C. Systemic activation of the coagulation system depletes some factors more rapidly than the liver can synthesize them.
• D. The patient has been misdiagnosed; a prolonged aPTT indicates that the problem is deficient, not excessive, coagulation.

Answer: (C)

In DIC, clotting is turned on all over the body, so clotting factors and platelets are consumed faster than they can be made or replaced. The liver tries to compensate by making more factors, but the ongoing systemic activation uses them up more quickly, leaving low levels in the circulation. Because the aPTT tests the intrinsic and common pathways, depletion of those factors causes a longer time to form a clot, producing a prolonged aPTT. This consumption of multiple factors across pathways is the hallmark of DIC’s effect on coagulation tests. The idea that only extrinsic factors are affected would more likely show a longer PT, not the broad consumption described here, and misdiagnosis isn’t the mechanism behind the prolongation.