Fibroblast Growth Factor 23 (Intact), Serum or Plasma — Mass Concentration
Measures intact FGF-23, a hormone that helps regulate phosphate and vitamin D levels.
["This test can help evaluate unusual FGF-23 activity, particularly when phosphate or vitamin D levels are abnormal."]
Key facts at a glance
- LOINC
- 53422-2
- Short code
- FGF-23.intact sp4 p chal Plas IA-mCnc
- Synonyms
- FGF-23.intact sp4 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 blood test measures intact fibroblast growth factor 23, or FGF-23. FGF-23 helps control how the kidneys handle phosphate and activate vitamin D.
Why might I need this test?
A clinician may order this test when phosphate or vitamin D results are unexpectedly low, or when bone pain, muscle weakness, or rickets or osteomalacia is suspected. It may also be used when excess FGF-23 activity is a concern.
How is the test performed?
A blood sample is collected, usually from a vein, and the amount of intact FGF-23 in the serum or plasma is measured using a laboratory method.
How do I prepare for the test?
You may be told to fast before the test, depending on the laboratory and the other tests being ordered. Vitamin D or phosphate supplements and medications may affect results, so tell the healthcare provider about everything you are taking.
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 FGF-23 result may indicate increased hormone activity, which can cause the kidneys to reduce phosphate reabsorption and suppress active vitamin D. This may be related to rare inherited disorders, vitamin D deficiency, or certain kidney conditions and is interpreted alongside phosphate, calcium, vitamin D, kidney function, and other findings. A result alone does not establish a diagnosis.
Short name
Intact FGF-23
Frequently asked questions
What does FGF-23 do?
What is meant by intact FGF-23?
Does an abnormal result confirm a specific condition?
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