Determinants of insulin concentrations in healthy 1-week-old babies in the community: applications of a bloodspot assay

BACKGROUND: Epidemiological research into insulin secretion and insulin action would be helped by improved ability to measure insulin concentrations in large groups of healthy babies in the neonatal period. Such research is often restricted by the invasive nature of blood sampling. AIMS: We assessed the use of an assay that can measure insulin from bloodspots taken during routine Guthrie testing 7 days after delivery. STUDY DESIGN AND SUBJECTS: Insulin and glucose were measured in 366 seven-day-old infants from heel-prick bloodspots. Time since last feed and type of feed were recorded. RESULTS: Bloodspot insulin concentrations in normal 7-day-old infants were much lower (median (IQR): 15.4 pmol/l (<10-28.5)) than fasting insulin concentrations in adult males (44.3 pmol/l (30.6-72.6)) (p<0.001). Insulin and glucose concentrations were correlated (r=0.33, p<0.001). Insulin and glucose fell significantly with time from feed. Bottle fed infants had higher insulin concentrations but similar glucose concentrations compared to breast fed infants. Detailed analysis to account for confounders was limited due to the skewed distribution of time since feed and the lower limit of the assay leading to non-continuous insulin data. CONCLUSIONS: In the largest study of normal 7-day-old children to date we have shown insulin concentrations are low compared to adults and vary with glucose, time from feed, and type of feed. This validates the use of the bloodspot insulin assay as a potential research tool for large-scale epidemiological studies. However, careful study design would be required in future use to reduce the variation caused by timing and type of feeding and the problem of one third of values being at or below the lower limit of this assay.