Background: Chronic kidney disease (CKD) is a major public health issue that imposes significant financial burdens on health systems across the world. Calcium and phosphorus levels in the blood are maintained by tubular reabsorption systems in the kidneys. Changes in the mineral metabolism occur as renal disease progresses. Chronic hyperphosphatemia causes FGF23 levels to rise in later stages of CKD. Bone cells are the major source of FGF23's secretion. The regulation of mineral ion homeostasis by FGF23 has been shown. Methods: Sixty youngsters will participate in the trial, which was done at the paediatric nephrology section of Benha University Hospital. Group I consists of 40 individuals with end-stage renal disease. Divided into the following groups based on GFR: Patients in CKD stages I, II, III, and IV were followed up in our paediatric nephrology clinic every three or six months, depending on their health. 2- Patients with CKD stage V were included in subgroup IB (n = 25). (undergoing regular hemodialysis three times per week, with each dialysis session lasting three to four hours). Group II: consists of 20 youngsters who seem to be in good health. It was made up of 10 men and 10 women, all of whom seemed to be of the same age, sex, and social status. Submissions came from all of the subjects: Blood count in its entirety (CBC), Serum creatinine level, blood urea nitrogen (BUN), serum calcium (Ca), serum phosphorus (Po4), serum alkaline phosphatase (ALP), parathyroid hormone (PTH), serum fibroblast growth factor 23 (FGF23) were all measured in this study. We discovered 24 patients with normal radiological results, 14 patients with subperiosteal bone resorption, seven patients with pathological fractures, and one patient with brown tumours (2.5 percent ). We found that the concentration of FGF23 in group I (532.5 pg/ml vs. 124.9 pg/ml) was statistically significantly higher than the control group (124.9pg/ml). We discovered a cutoff point of 159.7 pg/ml with a sensitivity of 85%, specificity of 90%, accuracy of 80%, PPV of 94.4 %, NPP of 75%, AUROC of 0.837, and a P value of 0.0001 for FGF23 in predicting CKD. It may be concluded that the early biomarker FGF 23 can be utilised to track the progression of chronic kidney disease in kids