Intact Fibroblast Growth Factor 23 (FGF-23) — Serum/Plasma, Mass Concentration
Measures intact FGF-23, a hormone that helps regulate phosphate levels, vitamin D activity, and bone and kidney function.
["An intact FGF-23 blood test helps evaluate phosphate regulation and may support evaluation of kidney, bone, or parathyroid disorders."]
Key facts at a glance
- LOINC
- 53424-8
- Short code
- FGF-23.intact sp6 p chal Plas IA-mCnc
- Synonyms
- FGF-23.intact sp6 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 is made mainly by bone and helps the kidneys control phosphate retention and vitamin D activation.
Why might I need this test?
Your clinician may order this test when phosphate levels are abnormal or when symptoms suggest a disorder affecting bone mineralization, kidney function, or parathyroid hormone activity. It can also help evaluate suspected tumor-related phosphate loss.
How is the test performed?
A blood sample is collected from a vein and sent to a laboratory, where intact FGF-23 is measured using a laboratory assay. The test may be interpreted alongside phosphate, calcium, vitamin D, kidney function, and parathyroid hormone results.
How do I prepare for the test?
Fasting is generally not required unless your clinician specifically requests it. Tell the healthcare professional ordering the test about any medicines or supplements that affect phosphate, vitamin D, bone health, or kidney function.
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 occur with reduced kidney function, vitamin D deficiency, or conditions that cause excessive phosphate loss, including certain inherited bone disorders and tumor-induced osteomalacia. A low result may be seen when phosphate is being retained, such as in some forms of hyperparathyroidism. Results must be interpreted with the other laboratory findings and the clinical situation.
Short name
Intact FGF-23
Frequently asked questions
What does FGF-23 do?
Does this test diagnose a specific condition?
Why might an FGF-23 test be ordered with a phosphate test?
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