BES2005 Poster Presentations Steroids (17 abstracts)
Background: The action of a steroid in any physiological process is dependent on the bioavailable (free) fraction. Direct measurements of free cortisol are expensive, labour intensive and require a significant volume of plasma and as a consequence are not feasible in the neonate. One alternative is to calculate free cortisol from the Cortisol Binding Capacity (CBC) and the total plasma cortisol. The aim of the present study was to develop an assay for the measurement of CBC in perinatal plasma.
Methods/Results: A sensitive, reproducible, inexpensive assay suitable for relatively routine measurement of CBC on a small volume of neonatal plasma was developed, based on the principles of saturation analysis. The assay was optimised for cortisol saturation, separation time and plasma dilution. The method is specific (Cross reactivity; Progesterone (12.5%), Dexamethasone (12.5%), Cortisone (0.8%), 17 Hydroxyprogesterone (0.8%), 11 deoxycortisol (0.2%), Prednisone (0.2%), 21 hydroxyprogesterone (0.2%), Testosterone (< 0.1%), Corticosterone (< 0.1%) and cholesterol (< 0.1%)) and reproducible (Intra-assay CV 6 % and Inter-assay CV 12 %). Consent for Cord blood obtained from elective sections (n=12) and adult blood (n=10) was obtained to study the CBC. Mean CBC from cord blood was 44 (SD plus/minus 21.5, range 19-83) nmol/l and from adult plasma 121.1 (SD plus/minus 67, range 47-265) nmol/l.
The CBC in newborn infants is significantly lower than in adults (p <0.005). This indicates that there may be more circulating free cortisol in the neonate than in the adult.