Fibroblast Growth Factor 23 (FGF23), Intact, Serum/Plasma — Immunoassay, Mass Concentration
Measures intact FGF23, a hormone that helps regulate phosphate, vitamin D, and bone mineralization.
["This blood test helps evaluate disorders that affect phosphate levels and bone health."]
Key facts at a glance
- LOINC
- 53421-4
- Short code
- FGF-23.intact sp3 p chal Plas IA-mCnc
- Synonyms
- FGF-23.intact sp3 p chal Plas IA-mCnc
- Category
- liver
- Sample
- plasma
- Container
- Lavender-top (EDTA) or Green-top (Heparin)
- Units
- N/A
- Ref low
- 44
- Ref high
- 147
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- ia
- CPT
- 84075
- SNOMED
- 27550007
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What is this test?
This test measures intact fibroblast growth factor 23, or FGF23, in blood. FGF23 helps control how the kidneys handle phosphate and vitamin D, linking bone health with mineral metabolism.
Why might I need this test?
A clinician may order this test when phosphate levels are unexpectedly high or low, or when bone or kidney disease is suspected. It can help assess whether too much FGF23 is contributing to phosphate loss, reduced active vitamin D, or weakened bones.
How is the test performed?
A blood sample is collected, usually from a vein. The laboratory uses an immunoassay to measure the amount of intact FGF23 in the serum or plasma portion of the sample.
How do I prepare for the test?
Fasting is usually not required, but follow the instructions provided by the laboratory or ordering clinician. Tell the care team about medicines, vitamin D supplements, and phosphate supplements because they may affect the result.
Reference range
Adult: 44-147 U/LN/A
No special preparation required. Avoid fatty meals before the test if possible.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
An elevated intact FGF23 level may indicate excessive FGF23 activity, which can cause the kidneys to lose phosphate and reduce active vitamin D. This may occur with some hereditary phosphate-wasting disorders, certain tumors, or advanced kidney disease. Results must be interpreted with phosphate, vitamin D, kidney function, and other clinical findings.
Short name
Intact FGF-23
Frequently asked questions
What does intact FGF23 mean?
Does an abnormal result diagnose a specific condition?
Can medicines or supplements affect the result?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy