Interpretations

Blood concentrations of IGF-1 remain constant during the day and after eating. Low IGF-1 and IGFBP-3 levels are observed in GH deficiency or GH resistance. Elevated serum IGF-1 levels indicate a sustained overproduction of GH, or excessive rhGH therapy. Malnutrition results in low IGF-1 levels, which recover with restoration of adequate nutrition. Concentrations of IGF-1 increase during the first year of life reaching the highest values in early adolescent years. Normal values tend to decline progressively until age 50 years and later.

Insulin-like growth factor 1 (IGF-1) measurements can be used to assess growth hormone (GH) excess or deficiency. IGF-1 measurement has generally been shown to have superior diagnostic sensitivity and specificity, and should be used as the primary test, in particular, in the diagnosis and follow-up of acromegaly and gigantism. The combination of IGF-1 and IGFBP-3 measurements appear superior in the diagnosis of GH deficiency and resistance, and in the monitoring of recombinant human GH (rhGH) therapy.

Increased concentrations of IGF-1 are normal during pregnancy however reference ranges on this population have not been formally established. Insulin-like growth factor 1 (IGF-1) reference ranges are highly age dependent and results must always be interpreted within the context of the patient's age.

IGF-1 assays exhibit significant variability among platforms and manufacturers, therefore values obtained by different assays cannot be directly compared. If IGF-1 is being used for serial monitoring, establishing baseline of patients, it is recommended assays should not be changed. For diagnostic purposes, the results obtained from assays should always be used in combination with the clinical examination, patient medical history, and other findings.