Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

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Which test could not be performed on a serum sample?

Iron
Vitamin B12
Total lipids
Clotting factors

The correct answer is: Clotting factors

The test that could not be performed on a serum sample is the assessment of clotting factors. This is because clotting factors are proteins that are involved in the coagulation cascade, and their measurement typically requires citrated plasma, not serum. Serum is obtained after the blood has been allowed to clot and the clot has been removed, which means that any clotting factors present will have been consumed in the clotting process. Therefore, when measuring clotting factors such as Prothrombin, Factor V, or others involved in hemostasis, the appropriate specimen type is citrated plasma. This specimen type preserves the activity of the clotting factors, allowing for accurate measurement and analysis. The other tests listed—iron, vitamin B12, and total lipids—can all be performed on serum samples, as they involve soluble analytes or metabolites that remain in serum after clotting has occurred.