Elevated ammonia concentrations: Potential for pre-analytical and analytical contributing factors.
Author(s): Hashim IA, Cuthbert JA
Publication: Clin Biochem, 2014, Vol. 47, Page 233-6
PubMed ID: 25175939 PubMed Review Paper? No
Purpose of Paper
The purpose of this paper was to determine the effects of preanalytical delay on the measurement of ammonium in EDTA plasma.
Conclusion of Paper
A higher percentage of specimens had elevated ammonium levels when the time from blood collection to result exceeded 120 min than when it was <120 min. Most of the processing delay was attributed to delays after arrival in the laboratory where centrifugation occurred, and when the delay from arrival to analysis was >90 min, there was a significant linear relationship between the delay and ammonium levels.
Studies
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Study Purpose
The purpose of this study was to determine the effects of preanalytical delay on the measurement of ammonium in EDTA plasma. 3625 measurements were made using blood collected from 1,835 patients that was transported and stored on ice until centrifugation and analysis. The mean transport duration was 9 min, but the method was not described. The timing of centrifugation relative to obtaining results was not specified so laboratory delays may include pre- and post-centrifugation storage of blood or plasma. An additional 2036 specimens from UT Southwest University Hospital were included in the study. No diagnoses were specified.
Summary of Findings:
When the time from blood collection to analysis was >120 min, 81% of specimens had elevated (>40µmol/L) ammonium levels, but when it was <120 min, only 56% had elevated ammonium levels (p<0.001). A second laboratory analysis of 2036 specimens found similar increases in the percentage of elevated results when specimens were held for >120 min rather than processed in <120 min (47% versus 58%, p=0.001). When results were broken down into 30 min windows, only the difference between specimens processed 90-119 min and those processed 120-149 min after collection was significant (59% vs. 74% p=0.034). Delays in the laboratory of >90 min were found for 91% of the specimens with processing times >120 min. For individual specimens, there was no relationship between the time from collection to arrival at the laboratory and ammonium levels, but time from arrival in the laboratory to result significantly affected ammonium levels (p<0.00005). When the time from arrival in the laboratory to analysis (including pre- and post-centrifugation storage) exceeded 90 min there was a significant linear relationship between the laboratory delay and the ammonium level (p=0.005).
Biospecimens
Preservative Types
- None (Fresh)
Diagnoses:
- Not specified
Platform:
Analyte Technology Platform Small molecule Clinical chemistry/auto analyzer Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Storage Storage duration <30 min
30-59 min
60-89 min
90-119 min
<120 min
>120 min
120-149 min
150-179 min
>180 min
Preaquisition Biomarker level <40 µmol/L ammonium
>40 µmol/L ammonium
<40 µmol/L ammonia
>40 µmol/L ammonia
Biospecimen Aliquots and Components Centrifugation Centrifugation delays investigated