In a vitamin K-deficient patient, which coagulation test(s) would be abnormal?

In a vitamin K-deficient patient, the abnormality in coagulation tests primarily reflects the role of vitamin K in the synthesis of certain clotting factors in the liver. Vitamin K is crucial for the post-translational modification of factors II (prothrombin), VII, IX, and X, which are involved in the coagulation cascade.

Prothrombin time (PT) is particularly sensitive to deficiencies in these vitamin K-dependent factors, especially factor VII, which has the shortest half-life among them. In a vitamin K deficiency scenario, increased PT indicates that the extrinsic pathway is affected, often reflecting a more systemic issue with coagulation.

Activated Partial Thromboplastin Time (APTT) can also be prolonged, although it is less sensitive to vitamin K deficiency compared to PT. APTT evaluates the intrinsic pathway of coagulation, which includes factor IX, another vitamin K-dependent factor. Therefore, if both PT and APTT are prolonged, it indicates that multiple pathways of coagulation are being affected.

In the context of vitamin K deficiency, both PT and APTT would very likely be abnormal, making this option the most comprehensive in capturing the effects of vitamin K deficiency on the coagulation tests. The fibrinogen