Preanalytical increase of ammonia in blood specimens from healthy subjects

Abstract

The course and magnitude of spontaneous increase in ammonia concentration in plasma on standing were investigated with EDTA-treated blood specimens from 36 healthy subjects with use of a sensitive and precise enzymic method. Over 90 min, the rates of increase were virtually constant at fixed temperature. The mean (and SE) rates at 0, 20, and 37 degrees C were 3.9 (0.23), 5.2 (0.23), and 25.2 (0.59) mumol/L per hour, respectively. At these temperatures, the plasma contributed at most 7%, 15%, and 10%, respectively, to the formation of ammonia in whole blood. In view of the medical needs and the measured rates of ammonia increase, an interval of 15 min between blood sampling and the start of centrifugation may be tolerated at a specimen temperature of 0 degree C. Rates of ammonia increase showed significant correlations with erythrocyte and platelet count as well as with the plasma activities of gamma-glutamyltransferase (EC 2.3.2.2) and alanine aminotransferase (EC 2.6.1.2).

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.…”

“…In some cases, blood was collected directly into Erlenmeyer flasks, evacuated glass tubes, or via syringe into dipotassium EDTA. 1,6 Other studies utilized microdiffusion or ion-exchange methods to determine ammonia concentration, which are methods not used today. 1,3 Furthermore, previous studies focused on storage of specimens for hours to days prior to ammonia analysis and various temperature conditions for storage.…”

“…1,3 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.…”