he authors used competitive protein binding assay and radioimmunoassay
to measure cortisol levels in 38 normal control subjects three times before
and three times after administration of 1 mg of dexamethasone. They found
significant interassay differences at 11:00 p.m. before dexamethasone and
at all three postdexamethasone times. Analysis of variance revealed
significant overall positive relationships between age and cortisol levels
measured by both techniques. Age correlated significantly with
postdexamethasone cortisol levels measured by radioimmunoassay but not when
measured by competitive protein binding assay. Clinicians should obtain
data from their laboratories as to appropriate cutoffs for cortisol
suppression on the specific assay used.Abstract Teaser