Reference range for serum cortisol in well preterm infants

Abstract

AIM To establish a reference range for serum cortisol concentrations in preterm 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 criteria: surfactant administration, arterial hypotension, acute or uncontrolled infection, ventricular haemorrhage II° or above, serum glucose < 2.2 mmol/l, exchange transfusion, stress as a result of any kind of examination or nursing for at least 4 hours before blood sampling. The cortisol value was measured once using radioimmunoassay in each infant.

RESULTS In appropriate for gestational age (AGA) infants (n = 37, median gestational age 27.7 weeks, median birthweight 1030 g) the distribution of the cortisol concentrations was non-Gaussian. These had a nearly normal distribution, when log₁₀ values of the data were used. The points determined by mean (2 SD) on the logarithmic scale were transformed back to the original units to provide a reference range: 73–562 nmol/l. Gestational age was significantly (p = 0.033) associated with cortisol values (log₁₀) with a regression coefficient (standard error) of −0.045 (0.020). Small for gestational age (SGA) infants (n = 8) had significantly higher cortisol values (median 357 nmol/l) than AGA infants (median 199 nmol/l) (p=0.028).

CONCLUSIONS There is a strictly defined reference range of serum cortisol concentrations in AGA preterm infants.