Elevated ammonia concentrations: potential for pre-analytical and analytical contributing factors

No study has explored the separate contributions of pre-analytical and analytical factors to hyperammonemia.

Laboratory information systems were queried for tests of ammonia concentrations over a 12 month period. Pre-analytic (collection to laboratory receipt) and analytic (laboratory receipt to result) elapsed times were determined.

Under routine conditions for 3626 tests, normal and elevated results were similarly distributed if the time from venipuncture to result was <120 min. Delays, during analysis performance and in transportation to the laboratory, potentially contributed to hyperammonemia in a small number of samples (n=96, 2.7%). Similar results were obtained from a second hospital with a separate laboratory.

Delays, in either transportation to the laboratory after collection or before completion of analysis, have the potential to elevate ammonia concentrations and may cause pseudo-hyperammonemia. Unexpectedly elevated ammonia concentrations need to be evaluated for errors in sampling handling.