Blood Ammonia Stability Revisited

Abstract

The instability of ammonia in whole blood has challenged clinical laboratory scientists to develop specimen collection and handling methods that produce reliable results for plasma ammonia concentration. Thirty-eight outpatients' plasma ammonia concentrations were measured after heparinized whole blood specimens from each subject were held for 5, 15, and 30 minutes at room temperature and "on-ice". The plasma ammonia concentration from whole blood maintained "on-ice" for 5 minutes was designated the "reference value". Plasma ammonia concentrations from whole blood maintained "on-ice" for 15 or 30 minutes prior to processing were not significantly different from the reference values (15 min., p~0.196; 30 min., p~0.512). Plasma ammonia concentrations from whole blood maintained at room temperature for 5, 15 and 30 minutes prior to processing were also not significantly different from the reference values (p~0.961, 0.610, and 0.948, respectively). These results suggest that reliable plasma ammonia concentrations may be obtained from heparinized whole blood maintained at room temperature for up to 30 minutes.

Analytical Validation of an Assay for Concurrent Measurement of Amino Acids in Dog Serum and Comparison of Amino Acid Concentrations between Whole Blood, Plasma, and Serum from Dogs

“…This deamidation reaction also releases ammonia, contributing to an increase in ammonia concentrations with increasing storage time. Ammonia was significantly increased after 72 h of storage at 4 °C and this finding is consistent with results from previous studies [ 23 ].…”

“…Another limitation of our study is the small sample size used for the short-term stability testing. While the results of this portion of the study may be considered preliminary, they do correspond well to what has been shown in the literature in regard to amino acid stability [ 21 , 22 , 23 , 24 ].…”

Extracorporeal Ammonia Clearance for Hyperammonemia in Critically Ill Patients: A Scoping Review

“…However, the estimation of clearance is problematic because ammonia is an unstable molecule [41, 42] and its levels are affected by sample temperature [30]. This requires specimen collection, handling, and transport on ice.…”

UK National audit of the measurement of ammonia

“…Increases in ammonia in whole blood are greater than those in plasma, with greater increases at higher temperatures. [14][15][16][17][18][19][20] In a study where blood was collected from healthy volunteers (n = 36), whole blood ammonia concentrations increased by 3.9 μmol/L per hour at 0°C, 5.2 μmol/L at 20°C and 25.2 μmol/L per hour at 37°C from a mean ammonia concentration of 23.0 μmol/L. In plasma ammonia concentrations increased by 0.4 μmol/L per hour at 0°C, 1.4 μmol/L per hour at 20°C and 4.2 μmol/L per hour at 37°C from a mean ammonia concentration of 23.0 μmol/ L. 14 Therefore, speedy delivery of the sample to the laboratory and rapid analysis is required to minimise such increases.…”

“…Pre-analytical factors, such as haemolysis, delayed sample separation and inappropriate sample storage, can lead to artificially high results. [13][14][15][16][17][18][19][20] Laboratories have an important role in optimising pre-analytical processes, for example, by providing clear guidance on sample collection and handling so that pre-analytical errors can be minimised. Quality goals and sample acceptance criteria need to reflect the clinical utility of the test.…”