Growth Hormone Test

IGF-1 Test Result Interpretations

By Jay H Mead MD

Within reference range:

An IGF-1 level within the reference range does not rule out adult growth hormone deficiency (AGHD), or the potential benefit of growth hormone (GH) administration to an individual patient. The diagnosis of AGHD requires GH stimulation testing, eg, arginine and GHRH (Ghigo et al. Bailliere’s Clin Endo and Metab 1998 Vol 12: 341-358). For antiaging purposes, Drs. Frackleton and Christensen (J Advancement in Med 1998 volume 11 (1): 9-25) developed the “cell replacement age” equation: CRA=115 (years)-[IGF-1/4] for IGF-1 levels less than 320ng/ml.

Below reference range:

An IGF-1 level below the reference range warrants further evaluation. This may represent adult growth hormone deficiency (AGHD) conditions that interfere with IGF-1 production (see below) and/or accelerated aging. The diagnosis of AGHD requires GH stimulation testing, eg, arginine and GHRH (Ghigo et al. Bailliere’s Clin Endo and Metab 1998 Vol 12: 341-358). There are many conditions that may benefit from GH replacement: osteoporosis, demyelinating conditions, obesity, insulin insensitivity, reduced fibrinolysis, myotonic dystrophy, Crohn’s Disease, hyperlipidemia, atherosclerosis, and cardiovascular disease. Other factors known to lower IGF-1 levels include: oral estrogen, protein calorie malnutrition, insulin deficiency, liver failure, hypothyroidism, pregnancy, glucocorticoid therapy, renal failure and acute catabolic stress (e.g., surgery, trauma, hip fractures and infectious disease).

Above reference range:

An IGF-1 level above the reference range may represent excessive replacement therapy, an acceptable finding in an otherwise healthy individual, or acromegaly. If the latter is a consideration, further evaluation is warranted.

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