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

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

Methods: 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.

Results: 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.

Conclusions: 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.