Fibroblast Growth Factor 23
| Label Mnemonic: | FGF23 |
| Epic code: | LAB7603 |
| Downtime form: | A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery |
Commercial Mailout Laboratory
6240-8 RCP
356-8593
6240-8 RCP
356-8593
Specimen(s):
Plasma
Collection Medium:
 |
| Red top tube 5 mL (Clot Activator) |
Minimum:
Preferred Minimum: 0.5 mL Serum
Absolute Minimum: 0.25 mL Serum
Absolute Minimum: 0.25 mL Serum
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:
Pediatric (<18 yrs): < or =52 pg/mL
Adults (> or =18 yrs): < or = 59 pg/mL
Adults (> or =18 yrs): < or = 59 pg/mL
Interpretive Data:
Increased fibroblast growth factor 23 (FGF23) concentrations are present in individuals with renal phosphate-wasting diseases such as autosomal dominant hypophosphatemic rickets (ADHR), autosomal recessive hypophosphatemic rickets (ARHR), X-linked hypophosphatemia rickets (XLH) and tumor induced osteomalacia (TIO). Clinically, FGF23 measurement is useful in the differential diagnosis of these hypophosphatemic diseases since the patient presents with high FGF23 levels along with hypophosphatemia. In other causes of hypophosphatemia, such as vitamin D deficiency, FGF23 levels are low. In FGF23-producing tumors, a decrease in FGF23 concentrations following surgery is a reliable indication of complete tumor resection.
Intact FGF23 concentrations are elevated in patients with TIO or XLH. A study detected elevations of intact FGF23 in 19 of 22 TIO cases (86%).(1) In XLH, elevations of intact FGF23 were observed in 88% of patients (9 of10 children and 13 of 15 adults).(2) While levels of intact FGF23 in XLH are usually elevated, FGF23 concentrations within the reference interval do not exclude the disease and should be interpreted in the setting of phosphate concentrations (ie, an FGF23 concentration in the upper level of the reference interval in the context of hypophosphatemia might be indicative of XLH). In ADHR, FGF23 concentrations are not consistently elevated, and the severity of renal phosphate-wasting may wax and wane; FGF23 concentrations are normal during quiescent periods when serum phosphate levels are normal, and they are elevated during active, hypophosphatemic phases of the disease.(3) FGF23 concentrations are influenced by factors such as phosphate intake and vitamin D therapy. Therefore, intact FGF23 levels are most informative in untreated patients.
Intact FGF23 concentrations are elevated in patients with TIO or XLH. A study detected elevations of intact FGF23 in 19 of 22 TIO cases (86%).(1) In XLH, elevations of intact FGF23 were observed in 88% of patients (9 of10 children and 13 of 15 adults).(2) While levels of intact FGF23 in XLH are usually elevated, FGF23 concentrations within the reference interval do not exclude the disease and should be interpreted in the setting of phosphate concentrations (ie, an FGF23 concentration in the upper level of the reference interval in the context of hypophosphatemia might be indicative of XLH). In ADHR, FGF23 concentrations are not consistently elevated, and the severity of renal phosphate-wasting may wax and wane; FGF23 concentrations are normal during quiescent periods when serum phosphate levels are normal, and they are elevated during active, hypophosphatemic phases of the disease.(3) FGF23 concentrations are influenced by factors such as phosphate intake and vitamin D therapy. Therefore, intact FGF23 levels are most informative in untreated patients.
Comments:
Useful for:
Diagnosing and monitoring tumor induced osteomalacia
Diagnosing X-linked hypophosphatemia or autosomal dominant hypophosphatemic rickets
Diagnosing familial tumoral calcinosis with hyperphosphatemia
Cautions:
Fibroblast growth factor 23 (FGF23) concentrations must be interpreted in conjunction with serum phosphate (phosphorus) measurements, as FGF23 will be elevated in other conditions that cause hyperphosphatemia in vivo. These include: renal failure, severe catabolic states (eg, severe systemic illness, uncontrolled type I diabetes mellitus, and severe starvation) vitamin D toxicity, intravenous phosphate treatment and very high phosphate diets, advanced malignancy in 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. Do not interpret FGF23 concentrations as absolute evidence of the presence or the absence of tumor induced osteomalacia (TIO). Some patients with TIO may have FGF23 levels within the reference interval. It is thought that tumors in these individuals may be secreting different, and yet unidentified, phosphatonins. Therefore, if the clinical picture and general osteomalacia laboratory workup suggest strongly that the patient has TIO; a normal intact FGF23 level should not discourage tumor search or removal.
Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedures, may have circulating anti-animal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results. Whenever the test results do not fit the clinical picture, the laboratory should be consulted regarding possible assay interference.
In vitro studies indicate that the presence of burosumab falsely decreases IFG23 results in a dose-dependent manner.
Patients receiving burosumab should not be monitored using the IFG23 assay. Serum phosphate, alkaline phosphatase, and 1,25(OH)2D measurements should be considered for monitoring response to therapy.
Diagnosing and monitoring tumor induced osteomalacia
Diagnosing X-linked hypophosphatemia or autosomal dominant hypophosphatemic rickets
Diagnosing familial tumoral calcinosis with hyperphosphatemia
Cautions:
Fibroblast growth factor 23 (FGF23) concentrations must be interpreted in conjunction with serum phosphate (phosphorus) measurements, as FGF23 will be elevated in other conditions that cause hyperphosphatemia in vivo. These include: renal failure, severe catabolic states (eg, severe systemic illness, uncontrolled type I diabetes mellitus, and severe starvation) vitamin D toxicity, intravenous phosphate treatment and very high phosphate diets, advanced malignancy in 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. Do not interpret FGF23 concentrations as absolute evidence of the presence or the absence of tumor induced osteomalacia (TIO). Some patients with TIO may have FGF23 levels within the reference interval. It is thought that tumors in these individuals may be secreting different, and yet unidentified, phosphatonins. Therefore, if the clinical picture and general osteomalacia laboratory workup suggest strongly that the patient has TIO; a normal intact FGF23 level should not discourage tumor search or removal.
Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or imaging procedures, may have circulating anti-animal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results. Whenever the test results do not fit the clinical picture, the laboratory should be consulted regarding possible assay interference.
In vitro studies indicate that the presence of burosumab falsely decreases IFG23 results in a dose-dependent manner.
Patients receiving burosumab should not be monitored using the IFG23 assay. Serum phosphate, alkaline phosphatase, and 1,25(OH)2D measurements should be considered for monitoring response to therapy.
Methodology:
Chemiluminescence Based Quantitative Sandwich Immunoassay
CPT Code:
83520