A wide range of new methods for measuring hGH concentrations are now available. Thus, there is a need to determine normal values for these techniques. We have used the time-resolved immunofluorometric method, Delfia hGH (Wallac, Turku, Finland) to establish normal hGH values in children and adolescents. This assay is a solid phase two site immunofluorometric method based on a direct sandwich technique involving two very specific monoclonal antibodies for the 22KDa form of hGH and the 1st IRP 80/505 as standard. Thirty healthy prepubertal children of normal height and weight were studied after obtaining informed consent from parents and children. Basal levels of IGF-1 and IGFBP-3 were measured in all children using commercial kits from Nichols Institute and DSL respectively. A powdered clonidine tablet (0.1mg/m2) was given orally and blood samples for hGH measurements were drawn at times-30′, 0′, 60′, 90′ and 120′. Statistical analysis was done using Student t test after confirmung that hGH peak levels were normally distributed. No significant differences were seen in hGH levels between boys and girls and these data were pooled together and presented as mean and ±SD and (range). Table
All children presented normal basal levels of IGF-I and IGFBP-3. The sensitivity of the hGH assay was 0.1U/L and the intra-assay variation at this level was less than 6%. hGH levels rose after clonidine in all children. The lower limit of the normal response as defined by mean -2SD, was 2,1 ng/mL. We speculate that this value may represent the cutoff value to exclude hGH deficiency in children with short stature undergoing a clonidine test with Delfia hGH measurements.
