Rules-Based Medicine

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Fibroblast Growth Factor 23 (FGF-23)

Ultrasensitive Immunoassay



Rules-Based Medicine’s (RBM) internally developed and manufactured ultrasensitive immunoassay to fibroblast growth factor 23 (FGF-23) based on the Simoa® bead technology can accurately quantitate sub-pg/mL levels of FGF-23 in human serum and plasma.

Fibroblast growth factor 23 is a hormone (32kDa) belonging to the FGF-19 subfamily. Its main function is to regulate mineral homeostasis, specifically phosphate reabsorption and inhibition of the enzyme to form activated vitamin D. FGF-23 is produced primarily by osteocytes and osteoblasts. However, under pathologic conditions, such as chronic inflammation, macrophages and other tissues (e.g. tumors) can also be sources of FGF-23. Signaling of FGF-23 occurs via the FGF receptors (FGFR), with or without klotho as the co-receptor. Interestingly, FGF-23 can be cleaved by pro-protein convertases into 2 separate fragments, effectively separating the binding sites for FGFRs and klotho. Overproduction of FGF-23 can cause rickets or osteomalacia and elevated levels have been correlated with adverse clinical outcomes in chronic kidney, cardiovascular, inflammatory bowel, and infectious diseases. These adverse clinical outcomes are most likely due to uncontrolled inflammation.

The link between FGF-23 and inflammation is partly due to its effect on the generation of active vitamin D, which downregulates inflammatory mediators, such as IL-6, IL-12, IL-23, TNFα, IFNγ, CRP, and fibrinogen. In addition, FGF-23 production can be induced by vitamin D and a variety of immune mediators: TGF-ꞵ2, TNFα, and NFκb. The constant high levels of FGF-23 in chronic kidney disease can lead to cardiovascular disease and infections, both leading causes of mortality in these patients. Independent of kidney disease and circulating mineral levels, elevated FGF-23 is associated with left ventricular hypertrophy, cardiac fibrosis, increased hypertension, and subclinical atherosclerosis, which may be due to its regulation of ACE2 expression and infiltration of inflammatory macrophages. RBM’s Simoa FGF-23 assay can be an essential tool in clinical studies to evaluate pharmaceuticals targeting FGF-23 or the FGFR/Klotho signaling pathway.


Swiss-Prot Accession Number: Q9GZV9

Alternate names for this biomarker include:

FGF-23, Phosphatonin, Tumor-derived hypophosphatemia-inducing factor

Simoa™ Services
Biomarker LLOQ*
(Serum and Plasma)
(Undiluted Samples)
Volume Required
Serum or plasma Other fluids**
Fibroblast Growth Factor 23 (FGF-23) 0.65 pg/mL 0.1625 pg/mL 100 µL 150 µL

* Lower limit of quantitation (LLOQ) represents the lowest amount of an analyte that can be quantitatively determined with acceptable precision. LLOQ is determined by performing 2-fold serial dilutions of Standard to be tested in triplicate over three runs. The percent coefficient of variation (CV) is calculated for each of the dilution replicates, and the LLOQ is determined as the concentration at which the CV is 30%.

** Cerebrospinal fluid, urine, tissue culture supernatants,  bronchoalveolar lavage, synovial fluid, tissue extracts, tears, skin washings, etc.

All assay services are performed in our CLIA-certified laboratory.
Intended for Research Use Only.