NORMAL RANGES FOR IMMUNOCHEMILUMINOMETRIC GONADOTROPIN ASSAYS

Objective: We sought to establish normative data for spontaneous and g onadotropin-releasing hormone (GnRH)-stimulated serum luteinizing horm one (LH) and follicle-stimulating hormone (FSH) levels measured by new immunochemiluminometric assays (ICMA) in children and adolescents. Me thods: Random serum samples were obtained from 375 normal subjects (0. 1 to 17.7 years, 230 female subjects). Intravenous GnRH stimulation te sts were performed in 41 normal subjects (4.8 to 18 years, 20 female s ubjects), Normal ranges were calculated by age and Tanner stage. Immun ochemiluminometric assays of LH and FSH concentrations were compared w ith levels obtained by a sensitive immunofluorometric assay and a less sensitive radioimmunoassay, Results: Random gonadotropin concentratio ns in normal children followed the pattern of transient elevation in i nfancy, low but measurable prepubertal levels, and markedly increased values at puberty. Spontaneous LH levels were higher in male infants b ut were not statistically different in boys and girls after infancy, M ean prepubertal LH was 0.04 +/- 0.04 IU/L (n = 66), rising 100-foId du ring puberty, Spontaneous FSH levels were much higher than LH values, were higher in female infants, and rose threefold at puberty. Peak GnR H-stimulated LH was identical in prepubertal boys and girls (1.8 +/- 1 ,3 IU/L, n = 17) and increased 20-fold at puberty, Mean peak GnRH-stim ulated FSH was highest in prepubertal female subjects, Luteinizing hor mone values measured by ICMA and immunofluorometric assay were highly correlated, but radioimmunoassay levels diverged markedly from ICMA le vels at lower concentrations, Because absolute levels were higher, FSH values correlated adequately in the three assays throughout the norma l physiologic range. Conclusions: Measurement of LH by ICMA is much mo re sensitive than older assay methods. Spontaneous LH can be accuratel y measured by ICMA to the very low levels present in normal prepuberta l children, providing a potentially important biochemical discriminato r of pubertal status. An ICMA GnRH-stimulated LH level greater than 5 IU/L is suggestive of maturing gonadotropin secretion. The ICMA LH ass ays provide significant enhancement in sensitivity; these assays shoul d be used when levels may be low, and by their accuracy may reduce the time and expense of testing procedures.