engleski

Serum osmolality: short (8 hours) and long term (1 month) sample stability

BACKGROUND-AIM: Changes in osmolality (hyper- and hypo-osmolality) are associated with increased morbidity and mortality. However, stability of serum for measurement of this critical analyte is unknown. Our aim was to investigate the short- (8 hours) and long-term (1 month) stability of serum osmolality. METHODS: Blood samples from 40 inpatients were collected in clot-activator tubes (Becton, Dickinson and Company, Franklin Lakes, USA) and centrifuged at 3220 g for 10 min (Hettich, Kirchlengern, Germany). Serum osmolality was measured in triplicate on OSMOMAT 3000 (Gonotech, Berlin, Germany) analyzer and mean values of the repeated measurements were used in the analysis. Primary tubes were left at room temperature (RT) for 8h, and aliquots were stored at -20 °C for 1 month. Statistical analysis was performed using the MedCalc Statistical Software version 16.2.0 (MedCalc Software bvba, Ostend, Belgium). The results were tested with Friedman test. P value <0.5 was considered significant. Deviations were assessed against reference change value (RCV) of 5.13%, as acceptance criterion. RESULTS: Median osmolalities (and interquartile range, IQR) were as follows: 295 (292.5–301) for baseline values, 294 (290–297.5) and 292 (288.5–296) for 8h at RT and 1 month at -20 °C, (in mOsmol/kg) respectively. Method CV was 1.1%. There was a statistically significant difference in osmolality concentration measured after 8 hours at RT and after one month at -20 °C, compared to baseline results (P<0.001). Deviations from baseline osmolality were within acceptance criteria, as follows: 0.6% (95% CI: 0.3–0.8) and 1.4% (95% CI: 0.8–2.1), for 8h at RT and after 1 month at -20 °C. CONCLUSIONS: Serum samples for osmolality measurement are stable if kept in primary tubes at RT up to 8h, or if stored aliquoted up to 1 month at -20 °C. This allows that osmolality is requested as add-on or reflex test during the same day, or even within 1 month (e.g. to be shipped to a reference laboratory).

preanalytical phase, osmolality, sample stability

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