IGFBP-3 low — interpreting it alongside IGF-1
Insulin-like growth factor binding protein 3 (IGFBP-3) is the principal carrier protein for circulating IGF-1 (~75-80% of IGF-1 is bound to IGFBP-3 in a ternary complex with acid-labile subunit). Low IGFBP-3 typically tracks low IGF-1 because both are GH-dependent — they're produced together in the liver in response to growth hormone signalling. The diagnostic value of IGFBP-3 is mainly as a check on IGF-1 interpretation: low IGF-1 with low IGFBP-3 confirms GH-axis suppression; low IGF-1 with normal IGFBP-3 suggests the IGF-1 reading is anomalous (often acute illness or assay variability).
Reference ranges
| Adult reference (lab-dependent) | 2.5 – 4.5 mg/L |
| Children and adolescents (peak) | 4 – 8 mg/L |
| Severe GH deficiency | < 1.5 mg/L |
| GH excess (acromegaly) | > 6 mg/L |
What this marker measures
IGFBP-3 is one of six IGF-binding proteins; it carries ~75-80% of circulating IGF-1. The remaining IGF-1 is in smaller binary complexes (IGFBP-1, -2, -4, -5, -6) or free (~1%). Hepatic IGFBP-3 production is GH-dependent, so IGFBP-3 mirrors IGF-1 in most physiological states. The clinical value is in the GH-axis workup: discordant IGF-1 and IGFBP-3 readings flag either lab error or unusual physiological states (severe nutritional deficiency, hepatic dysfunction).
Why might it be low?
- ·GH deficiency (pituitary or hypothalamic)
- ·Severe protein malnutrition
- ·Hepatic dysfunction (synthesis impaired)
- ·Severe chronic illness
- ·Renal failure
- ·Anorexia
Why might it be elevated?
- ·Acromegaly / gigantism
- ·GH or GHRH analogue therapy
- ·Pregnancy (modest rise)
- ·Some lung tumours (rare)
FAQ
Why test IGFBP-3 if IGF-1 already gave me an answer?+
As a sanity check, mainly. If IGF-1 is unexpectedly low or borderline, IGFBP-3 helps confirm whether it's a true GH-axis issue (IGFBP-3 also low) or assay noise (IGFBP-3 normal). It's standard in formal endocrine workup and not always needed for routine biohacker monitoring.
This page describes biomarker research and reference ranges for self-tracking and research-context discussion only. It is not medical advice, not a diagnosis, and not a substitute for a qualified physician. Take any concerns about your health to a clinician.
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