Fibroblast Growth Factor 23 (FGF23), Intact, Plasma — Mass Concentration
Measures intact FGF23 in plasma, a hormone that helps regulate blood phosphate and vitamin D levels.
["An intact FGF23 blood test helps evaluate disorders that cause abnormal phosphate loss or buildup."]
Key facts at a glance
- LOINC
- 53419-8
- Short code
- FGF-23.intact sp1 p chal Plas IA-mCnc
- Synonyms
- FGF-23.intact sp1 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 a blood sample. FGF23 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 levels are unexpectedly low or high, or when there is concern about rickets, osteomalacia, or a condition affecting phosphate regulation. It can also help assess FGF23-related causes of bone disease.
How is the test performed?
A blood sample is collected and analyzed in a laboratory using an assay designed to measure intact FGF23. The result is reported as a mass concentration, or amount of FGF23 per unit volume of blood.
How do I prepare for the test?
Fasting is usually not required, but follow the instructions provided by your clinician or laboratory. Tell the healthcare team about medicines or supplements that affect phosphate or vitamin D, because they may 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.
An elevated intact FGF23 level may indicate excessive FGF23 activity, which causes the kidneys to reduce phosphate reabsorption and lower active vitamin D. This can occur with phosphate-wasting disorders, including some forms of hereditary rickets or osteomalacia, and with certain tumors. Low or inappropriately normal results in the setting of high phosphate may suggest reduced FGF23 action, which can occur with kidney dysfunction or vitamin D excess.
Short name
Intact FGF23
Frequently asked questions
What does intact FGF23 measure?
Is fasting required for an intact FGF23 test?
Can medicines 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.
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Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy