title: UK Biobank Pilot Study: stability of haematological and clinical chemistry analytes.
abstract: 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 36 h, 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 36 h 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 36 h should give a representative value of the analyte concentration at time zero for that individual.
authors.affiliation: Department of Epidemiology and Public Health, Faculty of Medicine, St Mary's Campus, Imperial College London, Norfolk Place, London W2 1PG, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Jackson
authors.forename: Nicky
authors.initials: N
authors.lastname: Best
authors.forename: Paul
authors.initials: P
authors.lastname: Elliott
mesh_terms: D018070:Biological Specimen Banks; D001774:Blood Chemical Analysis / Q000592:standards; D015925:Cryopreservation; D006801:Humans; D010865:Pilot Projects; D010949:Plasma / Q000737:chemistry*; D017410:Practice Guidelines as Topic; D044967:Serum / Q000737:chemistry; D013048:Specimen Handling / Q000009:adverse effects; D013997:Time Factors; D006113:United Kingdom; D016482:Urinalysis / Q000592:standards; D014556:Urine / Q000737:chemistry*