Variability among five different commercial IGF-1 immunoassays in conditions of childhood-onset GH deficiency and GH therapy

IGF-1 measurement is used for screening of GH deficiency and monitoring of GH therapy in children. However, several commercial immunoassays are currently used and reference values provided by manufacturers are very different. The aim of this study was to compare commercial IGF-1 assays 1) in terms of absolute values and 2) in terms of clinical interpretation of results based on IGF-1 reference values in serum samples from children with GH therapy, with untreated GH deficiency and with obesity. Serum samples of 9 patients were sent frozen to 5 university hospitals using 5 different IGF-1 assays. The inter-laboratory coefficient of variation (CV) was calculated for the 9 samples. For clinical interpretation, results were expressed as SD scores based on reference values provided by manufacturers (and used in these laboratories). The mean inter-laboratory CV (range) for the 9 serum samples was 25.8% (16.7-35.9%). Major variability was noted in the SD-scores between IGF-1 assays for 3 tested serum samples from GH-treated patients with a difference between the lowest and highest SD score of 2.6 up to 3.2. In conclusion, there is a large variability among commercial IGF-1 immunoassays, not only in terms of absolute values, but also in terms of clinical interpretation in pediatric serum samples.There is a need for IGF-1 immunoassay harmonization and for the establishment of adequate reference values.