Insulin-Like Growth Factor 1 (IGF-1) is a hormone made mainly by the liver in response to growth hormone (GH) released by the pituitary gland. IGF-1 circulates in the bloodstream and helps drive cell growth, division, and repair across bones, muscles, and organs. Although it’s structurally similar to insulin, IGF-1’s primary role is supporting growth, tissue building, and long-term maintenance.

An IGF-1 test is commonly used because IGF-1 levels are more stable throughout the day than GH, which fluctuates in pulses. Measuring IGF-1 provides a reliable snapshot of overall growth hormone activity and how effectively the GH–IGF-1 axis is working. This makes IGF-1 helpful for evaluating growth, metabolism, tissue repair, and suspected growth hormone disorders.

IGF-1 testing can help explain unexplained fatigue, muscle weakness, changes in body composition, or unusual growth patterns by assessing growth hormone signaling. It may spot growth hormone deficiency or excess early and clarify whether symptoms stem from hormone imbalance versus other causes like nutrition or chronic illness. Results can also guide next steps, such as additional endocrine evaluation or targeted treatment planning.

Low IGF-1 typically suggests reduced growth hormone activity or impaired liver production of IGF-1. Causes can include growth hormone deficiency, malnutrition, chronic illness, liver disease, or poorly controlled diabetes. In children and adolescents, low IGF-1 may be linked to slowed height gain or delayed puberty. In adults, it can relate to fatigue, reduced muscle mass, increased body fat, fragile bones, and subtle cognitive changes.

High IGF-1 most often reflects excess growth hormone, commonly due to a pituitary adenoma that can cause acromegaly in adults (or gigantism in children). Persistently elevated IGF-1 can drive abnormal bone and soft tissue growth, joint pain, insulin resistance, and cardiovascular strain. IGF-1 may also rise with pregnancy or certain medications, but sustained elevation in adults typically warrants investigation for GH excess.

IGF-1 varies significantly by age: it peaks during puberty and declines steadily with aging. Because of these normal shifts, results should be interpreted using age- and sex-specific reference ranges. “Low” or “high” values can mean different things depending on life stage, including adolescence growth spurts or the natural decline seen in menopause and older adults. Accurate interpretation also considers symptoms and clinical context.

IGF-1 production depends on more than growth hormone alone. Nutritional status, liver function, thyroid hormones, and insulin sensitivity can all influence IGF-1 levels. Malnutrition, chronic illness, liver disease, or metabolic issues (including poorly controlled diabetes) may lower IGF-1 even if pituitary function is normal. Because multiple systems affect IGF-1, clinicians interpret results alongside health history and other labs.

IGF-1 testing helps guide dosing and decisions when someone is on growth hormone therapy by reflecting overall GH activity in the body. It’s also used to track response to treatment for growth disorders or pituitary tumor–related conditions affecting GH secretion. Monitoring IGF-1 over time can indicate whether therapy is achieving appropriate, age-adjusted levels without pushing IGF-1 too high.

An IGF-1 test is often a first-line indicator of GH axis function, but it may not fully confirm certain diagnoses. A growth hormone stimulation test is sometimes needed when IGF-1 results and symptoms suggest growth hormone deficiency or when the clinical picture is unclear. Because IGF-1 can be influenced by nutrition, liver function, and other hormones, stimulation testing can provide additional diagnostic certainty.

A common misconception is that IGF-1 works like insulin to regulate blood sugar. While IGF-1 is structurally similar to insulin, its main role is promoting growth, tissue repair, and cell survival across the body. IGF-1 does interact with metabolism and is influenced by insulin sensitivity, but it’s best understood as a key messenger of growth hormone rather than a primary blood-glucose regulator.