IGF-1 Blood Test: Age, Growth Hormone and Limits

Growth hormone is produced in the pituitary gland. Cells in the liver respond by producing IGF-1, which helps mediate growth. The liver-and-serum artwork illustrates this relationship; it does not show an exact organ structure or a measured hormone result.^{See reference 2}

Growth hormone secretion varies during the day, whereas IGF-1 is comparatively steadier. MedlinePlus describes IGF-1 rising toward puberty and declining during adulthood. A value suitable for one age cannot simply become another person's reference point.^{See reference 1}

A 2024 assay review describes substantial differences between methods and laboratories, as well as week-to-week variation within an individual. Updated reference populations can also change the upper reference limit. A chart copied from another test or an older report may therefore mislead.^{See reference 4}

Mayo's April 2026 notice replaced its IGFMS mass-spectrometry test with an IGF1S chemiluminescence immunoassay. It supplies age-specific, sex-specific and puberty-stage intervals. This is a concrete example of why the exact assay matters, not a recommendation to order that laboratory's test.^{See reference 5}

A high IGF-1 result can be part of investigating acromegaly, a condition involving excess growth hormone. NIDDK describes diagnosis using the clinical picture and blood testing, with further testing when appropriate. The result does not identify a pituitary tumour's size or prove a diagnosis independently.^{See reference 6}

A low result may accompany an age-related change or a growth-hormone disorder, but it is not specific to one cause. The acromegaly consensus also notes that nutrition, metabolic conditions and liver-related factors can affect IGF-1. Those influences need professional interpretation rather than a supplement or hormone response chosen from a number.^{See reference 1,See reference 3}

MedlinePlus says no special preparation is needed for an IGF-1 blood test.^{See reference 1}

However, Mayo's replacement-test notice gives an assay-specific precaution about biotin supplements. Confirm the instructions for your actual laboratory and disclose supplements. This guide does not tell you to stop a prescribed medicine.^{See reference 5}

For equivocal results in an acromegaly assessment, the 2024 consensus discusses repeating IGF-1 with the same validated assay. That recommendation belongs to a clinical assessment, not a self-directed screening schedule. Keep the method, reference interval and testing reason beside any trend.^{See reference 3}

The 2024 variability review focuses on people being assessed for acromegaly. It cannot establish an optimal IGF-1 for healthy ageing. This guide gives no longevity score, growth-hormone dose or bodybuilding clearance.^{See reference 4}