Studies in neonates, using blood sampling at 15 minute intervals, have demonstrated that cortisol (F) is secreted in discrete pulses approximately every 65 minutes. Deconvolution analysis is a mathematical technique which characterises pulses of hormone secretion over time in terms of two components; a pulse of secretion and a phase of elimination. The aim of this study was to determine the effect of less frequent blood sampling on deconvolution parameters for plasma F. Blood samples for plasma F were taken via indwelling arterial lines at 15 min intervals for 6 hours in 42 clinically stable neonates (median ga 32 wks, bw 1.95 kg) studied in the first 9 postnatal days. Characteristics of F secretion were estimated by deconvolution analysis for two groups of data; 15 min sampling (25 samples/6 hrs) and apparent 30 min sampling (12 samples/6 hrs). Pulsatile F secretion was observed in all infants. Data in the Table are given as median and inter-quartile range.

Table 1

We conclude that 30 min sampling vs 15 min. sampling underestimates the number of bursts and F production rate, and overestimates the interval between pulses and elimination half-life.