Igfbp3
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IGFBP-3
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I have enough to give a comprehensive overview. Here's a synthesis on IGFBP-3 (Insulin-like Growth Factor Binding Protein-3):
What it is
IGFBP-3 is the most abundant of the seven known IGF-binding proteins (IGFBP-1 through -7). It circulates bound to IGF-I (and IGF-II) with very high affinity (Kd 10⁻¹⁰ to 10⁻¹¹ M) - higher affinity than the IGF receptors themselves have for IGF - so IGFBPs act as the principal regulators/inhibitors of IGF bioactivity by controlling how much free IGF-I is available to bind receptors (Tietz Textbook of Laboratory Medicine, 7th Ed).
Physiology
- About 75-80% of circulating IGF-I/IGFBP-3 complexes are trimeric (IGF-I + IGFBP-3 + acid-labile subunit); the rest are smaller dimeric complexes. Less than 1% of IGF-I circulates free (Tietz Textbook, p. ~4119-4123).
- IGFBP-3 is growth hormone (GH) dependent - GH stimulates hepatic IGF-I production, and IGFBP-3 levels rise in parallel, since IGFBP-3 is the major carrier protein for circulating IGF-I (Harrison's Principles of Internal Medicine, 22nd Ed).
- IGFBP-3 also has biological actions independent of the IGF/IGF-I receptor axis, and its own dedicated receptors have been described.
- In cartilage, IGFBP-3 (unlike IGFBP-2 and -5, which are positive regulators) negatively regulates the anabolic (proteoglycan-synthesis-promoting) effects of IGF-I on chondrocytes (Firestein & Kelley's Textbook of Rheumatology).
Clinical use
- IGFBP-3 is used clinically as an adjunctive test alongside GH and IGF-I in the diagnosis of growth hormone deficiency and growth hormone resistance/insensitivity. Of all seven IGFBPs, it is the only one with established clinical relevance (Tietz Textbook of Laboratory Medicine).
- Low IGFBP-3 is typically seen with GH deficiency and malnutrition, mirroring low IGF-I (Harrison's Principles of Internal Medicine).
- In children, especially those under 10 years old, IGFBP-3 has higher specificity than IGF-I for detecting GH deficiency, because IGF-I reference ranges are very low and overlap heavily with the deficient range at young ages. It is part of the pediatric growth failure workup alongside karyotype/SHOX testing when indicated (The Harriet Lane Handbook, 23rd Ed).
- Reference intervals are strongly age- and sex-dependent, and also tracked by Tanner stage in adolescents. Example from the Harriet Lane Handbook:
- Ages 0-7 days: ≤0.7 mg/L, rising steadily through childhood
- Peaks around age 14-15 years (~3.3-10.0 mg/L) coinciding with pubertal growth spurt, then declines into adulthood
- Tanner stage-specific ranges also differ by sex (e.g., Tanner V female 2.7-9.1 mg/L vs. male 2.6-8.6 mg/L)
- In chronic kidney disease, there is GH resistance with elevated IGFBP-3 (and other IGFBPs) that impairs normal GH/IGF-I signaling; recombinant human IGFBP-3 (rhIGFBP3) and IGFBP "displacers" have been investigated as potential treatments for growth failure in CKD (Brenner and Rector's The Kidney).
Recent evidence (PubMed, last 2 years)
A 2025 systematic review/meta-analysis (PMID: 40600329, Growth Factors) examined IGF-1 and IGFBP-3 levels in children with central precocious puberty - relevant if the context of your question relates to pubertal timing rather than GH deficiency. If you're asking about a specific clinical scenario (e.g., a lab result, a pediatric growth evaluation, or a research context like cancer/senescence biology, where IGFBP-3 also has an emerging role), let me know and I can dig deeper into that specific angle.
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