Influences of specimen processing and storage conditions on results for plasma ammonia.

Ammonia concentrations in plasma may increase because of contamination and deterioration of blood components during specimen handling and storage. Using replicate specimens from healthy volunteers, we studied influences of specimen processing and storage procedures on ammonia measurements made with a self-contained reagent system. Under some conditions, ammonia concentrations more than doubled. The use of nonhemolyzed plasma specimens and prompt centrifugation, separation of plasma, and ammonia determination apparently were important in avoiding such increases, the duration of contact between plasma and cells being the most important factor. Lower temperatures had minimal effect on whole-blood storage and centrifugation, but retarded increases in ammonia in stored plasma. We conclude that procedures for collection and storage of specimens for ammonia determinations should be standardized and strictly observed.