FGF23 dosage with an automated assay: a single-center experience in patients with renal chronic disease

Abstract

A key pathogenic role in the development of secondary hyperparathyroidism in renal patients is played by the fibroblast growth factor 23 (FGF23), a 32 kDa protein secreted by osteocytes in response to dietary phosphorus load. FGF23 elicits a phosphaturic response and inhibits calcitriol synthesis. Measurement of FGF23 levels in patients with chronic renal insufficiency can be useful to better define abnormalities of calcium-phosphate metabolism as well as to select those patients in need of dietary interventions targeted to reduce phosphorus intake. Unfortunately, up to now some limits in its application as well as economic factors have prevented the routine use of FGF23 quantification in clinical practice. The aim of our study was to evaluate the circulating levels of FGF23 in patients with chronic kidney disease using the LIAISON® FGF23 (DiaSorin) assay, a new automated chemiluminescence method that measures the intact molecule and has been approved for clinical use. Twenty-three consecutive patients (14 males and 9 females, with mean age 72.3±10.9 years) with stage 3a-5ND CKD were enrolled. The FGF23 assay was also tested in 10 random patients with end-stage renal disease on hemodialysis. Serum levels of FGF23, PTH, 25(OH)VitD, calcium, phosphorus, creatinine and albumin were measured under fasting conditions. Within the CKD group, FGF23 serum levels were higher than normal in 16 cases. Serum FGF23 levels correlated significantly with serum phosphorus (r = 0.600, p<0.01), calcium (r = -0.546, p<0.05) and eGFR (r = -0.495, p<0.05). In particular, the negative relationship between residual renal function and circulating FGF23 was significant in patients with eGFR<30 mL/min/1.73mq (r = -0.636, p<0.05) but not in those with eGFR>30 mL/min/1.73 mq. Although from a small cohort of patients, our data confirm that FGF23 levels increase already in the early stages of CKD; they also confirm that when eGFR levels are <30 mL/min/1.73 mq FGF23 increases rapidly and linearly, reaching extremely high levels in the dialysis population. The availability of an automated assay quantifying the amounts of intact FGF23 molecule, and approved for clinical use by the European Community, represents a valuable tool for obtaining an optimal pharmacological and dietary management of patients with CKD-MBD since the earliest stages of renal disease.