IGFBP-3
The optimal range for IGFBP-3 (IGF Binding Protein 3) is commonly cited as Age-appropriate upper half of reference range, tighter than the standard lab reference range of 3.3–6.7 μg/mL (varies by age). Binds ~90% of circulating IGF-1 - the IGF-1:IGFBP-3 molar ratio refines interpretation of GH-axis activity.
How IGFBP-3 ranges relate
The standard lab range vs the optimization-focused target. Illustrative trajectory shows what a 12-week improvement pattern looks like — not real user data.
What IGFBP-3 Measures
IGFBP-3 is the main circulating carrier of IGF-1 - about 90% of IGF-1 circulates bound to IGFBP-3, which extends its half-life and modulates tissue availability. The IGF-1:IGFBP-3 molar ratio gives more information than IGF-1 alone: a high ratio suggests more "free" (bioactive) IGF-1, which matters in some clinical contexts.
Like IGF-1, IGFBP-3 rises with GH stimulation and falls with age. It is also used in pediatric GH deficiency workup and in some oncology risk assessments.
What Affects This Biomarker
IGFBP-3 is influenced by: GH status (moves in parallel with IGF-1), nutritional status (falls with protein restriction or illness), age (declines from peak in young adulthood), and directly by GH secretagogues.
In the Context of Peptide Protocols
Optional add-on when running tesamorelin, HGH, or MK-677 and wanting a more complete GH-axis picture. Not all users order it - IGF-1 alone is usually sufficient. When ordered, trend at baseline and 6 weeks alongside IGF-1.
Peptides That Commonly Move IGFBP-3
Frequently Asked Questions
What does IGFBP-3 measure?
IGFBP-3 is the main circulating carrier of IGF-1 - about 90% of IGF-1 circulates bound to IGFBP-3, which extends its half-life and modulates tissue availability. The IGF-1:IGFBP-3 molar ratio gives more information than IGF-1 alone: a high ratio suggests more "free" (bioactive) IGF-1, which matters in some clinical contexts.
What is the optimal range for IGFBP-3?
The optimal range for IGFBP-3 is commonly cited as Age-appropriate upper half of reference range. The standard lab reference range is 3.3–6.7 μg/mL (varies by age).
What affects IGFBP-3 levels?
IGFBP-3 is influenced by: GH status (moves in parallel with IGF-1), nutritional status (falls with protein restriction or illness), age (declines from peak in young adulthood), and directly by GH secretagogues.
Where This Fits in Your Panel
IGFBP-3 is one marker on a fuller panel. The Peptide Blood Work Checklist lays out the complete baseline panel, what to add by protocol type, and when to retest.
See the full blood work checklist →Upload any lab PDF and MyProtocolStack maps your values to IGFBP-3 and 40+ other biomarkers. StackAI interprets the trend in context of your protocol.
Start tracking →Last reviewed: June 2026
Informational only - not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.