Fibroblast Growth Factor 23
Label Mnemonic: FGF23
Epic Lab Code: LAB7603
Downtime Form: A-1a Miscellaneous Request
Commercial Mail-out Laboratory
5231 RCP
356-8593
Specimen(s):
Plasma
Specimen Instructions:
Fasting specimens are preferred for FGF23 measurement.
Collection Medium:
Pink top tube 6 mL (K2-EDTA)
Minimum:
1.5 mL Plasma to reference laboratory.
Rejection Criteria:
Grossly hemolyzed.
Delivery Instructions:
Deliver to laboratory immediately after collection.
Testing Schedule:
Test performed once a week on Tuesday.
Turn Around Time:
1 day upon receipt at reference laboratory.
Reference Range:
Results may be significantly elevated (ie, >900 RU/mL) in normal infants <3 months of age.

3 months-17 years: < or =230 RU/mL

> or =18 years: < or =180 RU/mL
Comments:
Useful for:
*Diagnosing and monitoring oncogenic osteomalacia
*Possible localization of occult neoplasms causing oncogenic
 osteomalacia
*Diagnosing X-linked hypophosphatemia or autosomal dominant
 hypophosphatemic rickets
*Diagnosing familial tumoral calcinosis with hyperphosphatemia
*Predicting treatment response to calcitriol or vitamin D analogs
 in patients with renal failure

Cautions:
FGF23 levels must always be interpreted in conjunction with serum phosphate measurements, as FGF23 will be elevated in most other conditions that cause hyperphosphatemia in vivo. These include: renal failure, severe catabolic states (eg, severe systemic illness, uncontrolled type I diabetes mellitus, severe starvation), vitamin D toxicity, intravenous phosphate treatment and very high phosphate diets (eg, diets based largely on processed meats, processed cheese or other dairy products), advanced malignancy (particular with tumor lysis), crush or other significant muscle injury or destruction, fractures, and some endocrine disorders, in particular hypoparathyroidism and acromegaly. With the exception of renal failure, FGF23 measurements will not contribute to diagnosis or patient management in these situations.
Methodology:
Immunometric Enzyme Assay
CPT Code:
83520