IGF-1 reference ranges are assay-specific: what to check on a lab report

IGF-1 numbers get compared across threads as if every lab measured the same thing. They do not. A consensus statement on GH and IGF-1 assays asked labs to calibrate against the WHO international standard (02/254), report results in mass units, and use reference intervals built for their own method, by age and sex.

When you discuss an IGF-1 result, the useful context is:

• the assay or platform named on the report, and the lab's own reference interval for age and sex;
• whether the result is also expressed as an SDS or z-score, which must still be interpreted in the context of the method and reference population;
• that one draw is one point: GH is secreted in pulses and IGF-1 integrates over time, which is what the archive's How much GH do we secrete in IUs? piece circles around.

Multicentre work published after the consensus built age- and sex-specific reference intervals for a single standardised immunoassay. It is a good illustration of how much the interval, not just the number, carries the meaning.

This thread is for interpreting assay methods and reference intervals. Individual results need a clinician; please do not post requests to interpret your own labs here.

Sources

1. Clemmons DR. Consensus statement on the standardization and evaluation of growth hormone and insulin-like growth factor assays. Clin Chem 2011;57(4):555–559. doi:10.1373/clinchem.2010.150631
2. Bidlingmaier M, Friedrich N, Emeny RT, et al. Reference intervals for insulin-like growth factor-1 (IGF-I) from birth to senescence: results from a multicenter study using a new automated chemiluminescence IGF-I immunoassay conforming to recent international recommendations. J Clin Endocrinol Metab 2014;99(5):1712–1721. doi:10.1210/jc.2013-3059