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.