Reference range for serum cortisol in well preterm infants

Aim-To establish a reference range for serum cortisol concentrations in pre term infants with a gestational age of less than 30 weeks during the first two weeks of life. Methods-Infants were prospectively classified by the following exclusion cr iteria: surfactant administration, arterial hypotension, acute or uncontrol led infection, ventricular haemorrhage II degrees or above, serum glucose < 2.2 mmol/l, exchange transfusion, stress as a result of any kind of examin ation or nursing for at least 4 hours before blood sampling. The cortisol v alue was measured once using radioimmunoassay in each infant. Results-In appropriate for gestational age (AGA) infants (n = 37, median ge stational age 27.7 weeks, median birthweight 1030 g) the distribution of th e cortisol concentrations was non-Gaussian. These had a nearly normal distr ibution, when log(10) values of the data were used. The points determined b y mean (2 SD) on the logarithmic scale were transformed back to the origina l units to provide a reference range: 73-562 nmovl. Gestational age was sig nificantly (p = 0.033) associated with cortisol values (log(10)) with a reg ression coefficient (standard error) of -0.045 (0.020). Small for gestation al age (SGA) infants (n = 8) had significantly higher cortisol values (medi an 357 nmol/l) than AGA infants (median 199 nmol/l) (p = 0.028). Conclusions-There is a strictly defined reference range of serum cortisol c oncentrations in AGA preterm infants.