Which lab pattern is most consistent with disseminated intravascular coagulation (DIC)?

• A. Normal coagulation tests.
• B. Prolonged PT; normal aPTT; normal platelets.
• C. Thrombocytosis with elevated fibrinogen.
• D. Prolonged PT/aPTT, thrombocytopenia, decreased fibrinogen in later stages, elevated D-dimer.

Answer: (D)

Disseminated intravascular coagulation is a consumption coagulopathy where widespread activation of coagulation uses up platelets and clotting factors, while also triggering fibrinolysis. This leads to a lab pattern that reflects both clot formation and factor consumption. The pattern that fits best shows prolonged PT and aPTT because both extrinsic and intrinsic pathways are affected by the consumed factors; low platelets from platelet consumption; fibrinogen decreasing as it is used up, especially in later stages; and elevated D-dimer from breakdown of cross-linked fibrin.

In early or less severe cases, fibrinogen might still be normal, but as the process progresses it falls, and D-dimer remains high due to ongoing fibrin degradation. The other patterns don’t match: normal coagulation tests would not indicate the systemic consumption; having only one coagulation test prolonged with normal platelets misses the broad consumption picture; and thrombocytosis with high fibrinogen is inconsistent with the platelet and factor consumption seen in DIC.