E-Poster Presentation ESA-SRB-ANZBMS 2021

Background

IGF-1 has long been a difficult analyte to measure, with well documented assay shifts in 2012. It became apparent that our current reference intervals (RI) were too high in the paediatric population and too low in the adult population. Issues around insufficient age partitioning in the paediatric population were also present.

Aims

To establish improved RIs for IGF-1, based on data from the local West Australian population. Assess the total variability (both biological and analytical) of IGF1.

Methods

IGF- 1 results between 2016-20, performed in PathWest laboratories, were assessed with gross outliers removed from the data. The remaining top and bottom 5 centiles were removed, leaving results that lie between the 5^th and 95^th centiles. Within the data set, patients with no history of pituitary disease or growth hormone disorder, who had 3 of more serial IGF1 tests done were identified, and analysed to assess total variability in IGF1.

Results

The resulting dataset contained 6943 results from 4230 patients. This data was used to derive a refence interval using local data as well as centile based continuous reference intervals. This data set is far larger than the 1500 patients used to derive the existing reference interval (as per kit insert) [1]. Within the data set, 91 patients with 301 results were identified as having no pituitary disease and had serial IGF1 measurements as part of an annual cardiovascular risk assessment. These results were used to assess IGF 1 variability.

Conclusion

Use of local data with a large number of patients and results is likely to provide a more reliable reference interval for our local population. Continuous centile based reference intervals may help identify patients whose results remain within the reference interval but whose centile has changed markedly.