Compare venipuncture and capillary puncture in terms of sample type, volume, and typical tests.

Compare venipuncture and capillary puncture in terms of sample type, volume, and typical tests.

• A. Venipuncture provides larger volumes suitable for chemistry and hematology requiring plasma/serum; capillary puncture yields small volumes and may be affected by tissue fluid contamination, often used for point-of-care glucose and newborn screening; not all tests are valid with capillary blood.
• B. Venipuncture yields serum; capillary yields plasma
• C. Capillary puncture yields larger volumes than venipuncture
• D. Both yield identical sample types and volumes for all tests

Answer: (B)

The key idea here is how the liquid portion of blood changes with processing. If you draw blood from a vein and let it clot, the liquid you obtain after centrifugation is serum (it lacks clotting factors). If you collect blood with an anticoagulant, or process capillary blood into an anticoagulant tube and then spin it down, you get plasma (the liquid portion still contains clotting factors). Venipuncture typically provides enough volume to allow processing into serum or plasma depending on the test needs, while capillary puncture yields much smaller volumes and is often used when only a tiny amount is required. In practice, many routine tests on venous blood are run on serum or plasma after appropriate processing, whereas capillary samples are commonly used for rapid tests like glucose or for screening that requires only small volumes. So the general distinction—venipuncture yields serum after clotting, capillary puncture yields plasma when anticoagulated—is a useful way to summarize how sample type and volume influence test selections.

The key idea here is how the liquid portion of blood changes with processing. If you draw blood from a vein and let it clot, the liquid you obtain after centrifugation is serum (it lacks clotting factors). If you collect blood with an anticoagulant, or process capillary blood into an anticoagulant tube and then spin it down, you get plasma (the liquid portion still contains clotting factors). Venipuncture typically provides enough volume to allow processing into serum or plasma depending on the test needs, while capillary puncture yields much smaller volumes and is often used when only a tiny amount is required. In practice, many routine tests on venous blood are run on serum or plasma after appropriate processing, whereas capillary samples are commonly used for rapid tests like glucose or for screening that requires only small volumes. So the general distinction—venipuncture yields serum after clotting, capillary puncture yields plasma when anticoagulated—is a useful way to summarize how sample type and volume influence test selections.