Endocrine Abstracts

The adrenal function of children is investigated similarly to adults’ using at rest (basal) and after testing serum cortisol concentration ((F)). di Iorgi et al. (JCEM 95:2132) showed a good diagnostic accuracy of glucagon testing investigating (F) increase. We retrospectively addressed the relevance of using, in children with short stature tested for GH deficiency, 1/ the normal reference range of our assay for basal (F) and 2/ the threshold provided by di Iorgi et al. on (F) response to glucagon-betaxolol testing. This population was not suspect of adrenal insufficiency.

Basal (F)DXi (N=140, 10.3 (0.2–15.5) yr (median (2.5th–97.5th percentile)) was 260 (98–604) nmol/l. 26% subjects had lower (F)DXi than the reference range (185–624) nmol/l (Unicel DXi800,Beckman Coulter).

After betaxolol-glucagon testing (N=108), GH peak was 34.8 (80–74.4) mUI/l (Liaison analyser, DiaSorin); 29% were low GH responders (peak<20 mUI/l). (F)DXi peak was 502 (117–856) nmol/l. 31% would be considered adrenal insufficient using di Iorgi et al.’s criterion (403 nmol/l: 100% specificity threshold). (F)DXi was compared with results obtained with our prior RIA assay in a subgroup of patients. Basal (F)RIA was 411 (141–1061) nmol/l. 7% subjects had lower (F)RIA than the reference range (200–800) nmol/l. (F)RIA peak was 770 (281–1542) nmol/l. 5% would be considered adrenal insufficient using di Iorgi et al.’s criteria. Passing-Bablock regression showed a significant linear relationship between data from the 2 assays with a significant bias.

This emphasizes again that laboratories have to provide reference values for given populations, (e.g. basal (F) in children with short stature). Clinically relevant thresholds have to be locally defined (e.g. betaxolol-glucagon testing). Data issued from manufacturer’s-chosen populations and clinically relevant thresholds established in well-conducted study but with different populations or assays cannot wholly substitute to local references. Failure to do so will elicit false positive or negative results.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.