Intact Fibroblast Growth Factor 23 (FGF23), Serum/Plasma — Mass Concentration
Measures intact FGF23, a hormone that helps regulate phosphate, vitamin D, and bone mineral balance.
["This blood test helps evaluate causes of abnormal phosphate and vitamin D metabolism."]
Key facts at a glance
- LOINC
- 53423-0
- Short code
- FGF-23.intact sp5 p chal Plas IA-mCnc
- Synonyms
- FGF-23.intact sp5 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 and mineral metabolism.
Why might I need this test?
A clinician may order this test when phosphate or vitamin D levels are unexpectedly low or high, or when bone pain, muscle weakness, or fractures suggest a mineral-metabolism disorder. It may also be used when kidney disease is affecting phosphate balance.
How is the test performed?
A blood sample is collected, and the serum or plasma is analyzed in the laboratory with an immunoassay. The result is usually reported as the concentration of intact FGF23.
How do I prepare for the test?
Fasting is generally not required, but follow the laboratory's instructions. Tell your clinician about vitamin D supplements, phosphate-containing products, and medicines that may affect mineral metabolism, because these can influence 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.
Elevated FGF23 may occur with reduced kidney function or conditions that cause the body to retain phosphate. Lower FGF23 may be seen with disorders that cause excessive phosphate loss, including uncommon FGF23-producing tumors. Results should be interpreted with phosphate, calcium, kidney function, vitamin D, and other findings because no single level establishes a diagnosis.
Short name
Intact FGF-23
Frequently asked questions
What does FGF23 do?
Does a low FGF23 result mean I have a bone disorder?
Can vitamin D supplements change 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