The impact of delayed processing of chilled whole blood specimens on the measurement of nutritional biomarkers in the UK National Diet and Nutrition Survey rolling programme

Abstract

BackgroundThe logistics of timely processing of blood specimens remains a barrier in population health studies to the generation of micronutrient status data. ObjectiveTo test a blood specimen processing protocol that includes overnight postage with cooling and its effect on nutritional biomarker concentrations. MethodsThis study was embedded within the UK National Diet and Nutrition Survey (NDNS). Paired specimens were collected from 64 participants (16 y+). One set of specimens was processed within 2-hours of collection [“field”] and paired samples mailed in an insulated box with cold packs using an overnight postal service to a central laboratory [“postal”]. Specimen processing protocols were aligned across field sites and the central laboratory. Specimens were frozen and later analysed using established methods for vitamins, minerals, lipids, ferritin and C-reactive protein (CRP). Percent difference was calculated between protocols and compared with quality specifications determined from intra- and inter-individual variation. ResultsIn the postal protocol, ferritin (6%(3, 8)) (geometric mean percent difference(95% CI)) (P=0.002) and zinc (4%(1, 6)) (P=0.004) were higher compared with the field protocol. Retinol (-3%(-4, -1) (P<0.0001)) and selenium (-3%(-5, -1) (P=0.003)) concentrations were lower in the postal protocol whereas total (2%(1, 3)) and HDL (4%(2, 5)) cholesterol were higher (P<0.0001) than in the field protocol. Percent differences were within the optimum quality specification for the majority of biomarkers, but ferritin, zinc and selenium fell outside of the optimum limits. Higher ferritin concentration in the postal protocol led to a decrease in the proportion of specimens with ferritin concentration <15 μg/L from 13% to 9%. ConclusionsThe majority of micronutrient biomarkers, serum lipids and CRP were minimally affected by delayed processing when cooled. The study suggests acceptable stability of nutritional biomarkers within the described protocol, which can provide accurate data for nutritional biomarkers commonly measured in studies and surveys.