Plasma is the preferred specimen for which of the following analytes?

The preference for plasma as a specimen for testing ammonia levels is due to the stability and preservation of ammonia in plasma compared to other specimen types. Ammonia is a volatile substance that can rapidly diffuse across cell membranes, leading to potential contamination and increased levels if whole blood or separated serum is used for testing.

Plasma, which is obtained from anticoagulated blood, provides a more consistent and reliable measurement of ammonia levels, as it reduces the risk of increased levels due to cellular metabolism. This makes it the preferred specimen type for ammonia analysis.

While plasma could also potentially be used for the other analytes listed, certain factors (like stability, sample handling, and the nature of the analyte) lead to plasma being specifically more suitable for ammonia testing. These aspects are crucial in the context of clinical laboratory practices, where accurate and reliable test results are paramount for patient care.