Clinical Information

Insulin-like growth factor 1 (IGF1) reference values are highly age dependent, and results must always be interpreted within the context of the patient's age. A non-pathological result does not always rule out the presence of growth dysfunction and should be interpreted together with other diagnostic procedures. Diagnosis of a growth disease should not be based on the result of a single test, but should be determined in conjunction with clinical findings in association with medical judgement. Any therapeutically decision must also be taken on a case-by-case basis. During normal pregnancy, serum IGF1 increases, on average, almost 2-fold (range approximately 1.1-fold to approximately 4-fold) over prepregnancy baseline concentrations; however, reference values for this population have not been formally established at our institution. IGF1 assays exhibit significant variability among platforms and manufacturers. Direct comparison of results obtained by different assays is problematic. If IGF1 is used for serial monitoring, reestablishment of the patient's baseline levels is preferred if assays are changed. Several amino-acid benign alterations within IGF1 have been discovered. At least 4 of these are known to result in IGF1 isoforms with diminished biological activity. IGF1 immunoassays vary in their ability to detect these reduced-function variants. Detection of the variant proteins may result in an overestimation of functionally active IGF1 in an affected patient. Mass spectrometry (MS)-based IGF1 assay can usually selectively detect the active IGF1 isoforms and is recommended. However, there might be as yet unknown functionally different variants of IGF1, which even MS cannot distinguish from wildtype (normal) IGF1.