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

Abstract

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.

Blood Ammonia Stability Revisited

“…The rates of increase estimated in these studies ranged from only 2-4 µmol/L per hour at 0-4 o C, and 5-6 µmol/L per hour at 20-22 o C, although confidence limits on these rates of increase were not given. 4,6 In our study, we observed no statistically significant difference in plasma ammonia concentrations after heparinized whole blood was held for 5, 15, or 30 minutes either "on ice" or at room temperature. These findings were not unexpected, after extrapolating the published hourly rates of increase in ammonia concentration back to the time points that we examined, and given the published analytical standard deviations for current methods for measuring ammonia.…”

“…These findings were not unexpected, after extrapolating the published hourly rates of increase in ammonia concentration back to the time points that we examined, and given the published analytical standard deviations for current methods for measuring ammonia. 4,6,11 In a recent retrospective study, Hashim and Cuthbert examined the plasma ammonia results for over 1,800 patients, where samples were collected in EDTA and transported on ice. They found no significant relationship between ammonia levels and pre-analytical time up to 30 minutes, and concluded that ammonia results are reliable if the total time that elapses from collection to result is <120 minutes.…”

“…1 Numerous studies have shown that plasma ammonia levels increase in vitro over time and may be falsely elevated if the specimen is not chilled "on-ice" prior to processing and analysis. [1][2][3][4][5][6][7] The sources of the increase in plasma ammonia concentration in vitro reportedly include deamination reactions in erythrocytes and platelets, and the deamidation of plasma glutamine by γglutamyltransferase (γ-GT). 4,6,[8][9][10] While these studies demonstrated the clinical importance of plasma ammonia specimen integrity, many of these studies were performed with blood collection techniques and analytical methods that are no longer in use.…”

“…1,3 Furthermore, previous studies focused on storage of specimens for hours to days prior to ammonia analysis and various temperature conditions for storage. [1][2][3][4][5][6] Based upon the aforementioned studies, the established procedure at Parham Doctors' Hospital (Hospital Corporation of America, Richmond, VA) requires that any blood specimen collected for plasma ammonia measurement not received "on ice" be rejected, regardless of how soon after collection the specimen is received in the laboratory. Rejection of a specimen delays analysis, reporting of results, diagnosis, treatment, and potentially increases the cost of providing healthcare.…”

Diagnostic Value of Fasting Plasma Ammonia and Bile Acid Concentrations in the Identification of Portosystemic Shunting in Dogs

“…It is thus impossible to send samples to a specialized laboratory by mail. [42][43][44][45][46] Although several authors mention this problem as the main reason for avoiding the use of AMM tests, this disadvantage has been largely resolved by the introduction of the Blood Ammonia Checker II. e This analyzer proved to be a simple, reliable, and relatively inexpensive alternative to the standard automated enzymatic assay.…”