UK Biobank pilot study: Stability of haematological and clinical chemistry analytes

Background Analytes in blood and urine may vary over time according to conditions of transport and storage. Methods UK Biobank pilot study to investigate stability through time of 42 haematological and clinical chemistry analytes in blood and four analytes in urine, kept in storage for up to 36h, for 40 individuals. Random effects linear regressions were used to model the change through time in repeated assay results on a sample, allowing for heterogeneity between individuals and assay variability. Results Assay results for most analytes tended to show a small negative bias (1-3% per 12 h stored) over time on average. Statistically significant (P < 0.05) heterogeneity in time trends between individuals, found for nearly all analytes, was dominated by differences in the baseline (time 0) assay results with the possible exception of Mean Corpuscular Haemoglobin Concentration (MCHC). Four out of 46 analytes (serum calcium, cholesterol, fibrinogen and HDL cholesterol) had a predicted probability of a negative time trend for a future individual > 0.9. Results for freeze-thaw samples were not materially different from those for non-freeze-thaw samples, except that stability of the analyte results was only assessed up to 12 h. Conclusions The results suggest that any instability in assay results up to 36h is likely to be small in comparison with between individual differences and assay error, and that a single assay measurement at any time between 0 and 36h should give a representative value of the analyte concentration at time zero for that individual.