Difficulties in Interpreting IGF-1 Levels in Short Stature Children Born Small for Gestational Age (SGA) Treated with Recombinant Human Growth Hormone (rhGH) Based on Data from Six Clinical Centers in Poland

The assessment of IGF-1 concentrations is one of the parameters used for evaluating response to rhGH treatment. An increase in IGF-1 concentration positively correlates with growth improvement, whereas IGF-1 concentrations significantly above the reference range may increase the risk of possible side effects. The aim of this study was to evaluate the IGF-1 local reference ranges for the rhGH treatment centers concerned and to compare these values with the population reference ranges. A retrospective analysis was conducted on auxological data from 229 SGA patients who received rhGH treatment between 2016 and 2020 at six university clinical centers in Poland. The IGF-1 levels were assessed at baseline, after 12 and 24 months, and compared to the reference ranges provided by the local laboratory and to the population reference ranges. After 12 months, 56 patients (24%) presented IGF-1 values > 97th percentile for the local reference range, whereas only 8 (3.5%) did so using the population reference ranges; p < 0.001. After 24 months of treatment, the values were: 47 (33%) > 97th percentile by local vs. 6 (4.2%) by population standards; p < 0.001. Thirty-nine patients had rhGH dose reduced after 12 months, of whom twelve (25%) had IGF-1 > 97th percentile according to the local reference ranges and five (13%) > 97th percentile for the population. Our data suggest that different methods used to determine IGF-1 concentration and the different IGF-1 reference ranges result in a significant proportion of rhGH-treated children with elevated IGF-1 concentration and experiencing dose reductions, which may negatively affect growth rate.