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Intact Fibroblast Growth Factor 23 (FGF-23), Plasma — Concentration

Published: August 9, 2026Updated: August 16, 2026

Measures intact FGF-23 in plasma, a hormone that helps regulate blood phosphate and vitamin D. The test may help evaluate phosphate and bone-mineral disorders.

Quick summary

["This blood test measures a hormone that controls phosphate levels and vitamin D activity."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
47854-5
Short code
FGF-23.intact Plas-aCnc
Synonyms
FGF-23.intact Plas-aCnc
Category
liver
Sample
plasma
Container
Lavender-top (EDTA) or Green-top (Heparin)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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, also called FGF-23, in a blood sample. FGF-23 helps the kidneys control phosphate and influences vitamin D metabolism.

Why might I need this test?

A clinician may order this test when phosphate levels are unexpectedly low or high, or when a bone or calcium-phosphorus disorder is suspected. It can also help evaluate certain causes of excessive phosphate loss in the urine.

How is the test performed?

Blood is collected from a vein, usually in an outpatient setting. The plasma is analyzed in the laboratory to determine the concentration of intact FGF-23.

How do I prepare for the test?

Fasting is usually not required, but follow the laboratory's specific instructions. Tell your clinician about vitamin D or phosphate supplements and other medicines because they may affect the results.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Elevated FGF-23 may occur with reduced kidney function, phosphate loss through the kidneys, or disorders that affect vitamin D activation. Markedly elevated levels can occur with a tumor that secretes FGF-23 and causes phosphate wasting. Results must be interpreted with kidney function, phosphate, calcium, and vitamin D measurements because these factors influence FGF-23.

Short name

Intact FGF-23, Plasma

Frequently asked questions

What does FGF-23 do?
FGF-23 helps regulate phosphate and vitamin D so that mineral levels remain balanced. It primarily acts through the kidneys and bones.
Does this test require fasting?
Fasting is generally not required. However, supplements, kidney disease, and certain medicines can affect FGF-23 levels, so preparation should follow your clinician's and laboratory's instructions.
Can a high FGF-23 result identify the exact cause?
No. A high result usually requires evaluation with other tests, including phosphate, calcium, kidney function, and vitamin D. It may prompt further assessment for kidney disease or an FGF-23-producing tumor.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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