FGF23
Also called: fibroblast growth factor 23, FGF-23
What it means
FGF23 is a hormone made by bone cells that tells the kidneys how much phosphate to keep or remove and helps regulate active vitamin D.
FGF23 shows that your bones help control phosphate and vitamin D balance throughout your whole body, not just your skeleton.
FGF23 (fibroblast growth factor 23) is a hormone made mostly by osteocytes, the mature cells that live deep inside bone. Its main job is controlling phosphate levels in the blood. It travels to the kidneys and, working with a protein called α-Klotho, tells them to get rid of extra phosphate and slow down the production of active vitamin D.
This makes bone an active participant in whole-body mineral balance, not just a storage site. FGF23 works alongside parathyroid hormone and vitamin D in a feedback loop: when phosphate or vitamin D levels shift, FGF23 helps bring things back into balance by adjusting what the kidneys keep or release.
FGF23 is especially relevant in chronic kidney disease, where levels tend to rise and have been linked to heart and blood vessel problems. Because of this, researchers see FGF23 as a bridge between bone health, kidney function, and cardiovascular risk. If you have kidney disease or unusual phosphate or vitamin D results, your doctor may consider FGF23 as part of the bigger picture, though it isn't a routine test for most people focused on bone density alone.
FGF23, a hormone from bone cells, helps control phosphate and vitamin D balance throughout the whole body.
Where this leads
WordFGF23 manages phosphate levels behind the scenes. See how a simple blood test checks that same phosphate balance and what abnormal levels might signal.
Where the Academy teaches it
This page is the short version. The lessons teach it in full, with the context around it and a quiz to lock it in.
Related words
Osteocytes are the most common bone cells. They used to be bone-builders but got trapped inside bone tissue, where…
Vitamin D is a nutrient that helps your gut absorb calcium so it can be used to build and maintain bone.
Chronic kidney disease is a long-term decline in kidney function that can disrupt vitamin D activation and the…
CKD-MBD is a bone and mineral problem caused by chronic kidney disease. As kidneys fail, they can't properly balance…
A parathyroid hormone (PTH) test measures the amount of PTH in your blood, usually alongside calcium, to help find…
A phosphate test measures the amount of phosphorus in your blood. Phosphate works closely with calcium to build…
Education only, not medical advice. Decisions about tests, medications and treatment belong with your own doctor. OsteoStrong does not diagnose, treat or cure any disease.
