Longitudinal Study to Find the Association of Serum Phosphorus Level with FGF23 in Three Different Hyperphosphatemia Management Groups of Stage 3 and 4 Chronic Kidney Disease (CKD) Patients.

Background: There is paucity of clinical evidence on target serum phosphorus levels in early chronic kidney disease (CKD). Present longitudinal study was done to find target phosphorus level and its association with fibroblast growth factor (FGF23) in three different hyperphosphatemia management groups. Methods: This 1-year, prospective, randomized controlled, open-labelled study was conducted among three equally allocated treatment groups that consisted of 120 screened early CKD patients totally. Group 1 patients were given dietary phosphorus modification (n = 40), group 2 patients were administered calcium-based phosphate binders (n = 40), and group 3 patients were given non-calcium-based phosphate binders (n = 40). Three-monthly dietary assessment, MDRD estimated glomerular filtration rate (eGFR), phosphorus, calcium, iPTH, alkaline phosphatase, and six-monthly FGF23, 2D echocardiography, and X-ray of chest and abdomen were performed. Association of three categories of phosphorus level up to 3.9, 4-5, and >5mg/dl, rate of progression of all parameters, and correlation with FGF23 were studied among all three groups. Results: At baseline, all clinical and biochemical parameters were equally distributed with a controlled nutritional phosphate among all groups. There was no significant difference of FGF23 levels from all the three categories of phosphorus level among all groups. Serum phosphorus at the level of 5 mg/dl was associated with iPTH and eGFR at 1 year. Over 1 year, there was a significant decline in serum phosphorus levels in group 1 (P 0.02), group 2 (P 0.00), and group 3 (P 0.05). FGF23 declined significantly only in group 3 (P 0.00). There was no correlation of FGF23 with serum phosphorus levels (P 0.13). However, FGF23 correlated positively with iPTH (P 0.03, r = 0.19). Conclusion: Serum phosphorus levels upto 5mg/dl had no effect on FGF23 at early CKD stages. Although different treatment groups showed significant phosphorus reduction, non-calcium phosphate binder had a major impact on FGF23 reduction.