The evaluation of renal osteodystrophy in kidney-transplanted children

Aim: The aim of this study was to evaluate kidney-transplanted pediatric patients from the renal osteodystrophy point of view, to show the effects of renal transplantation on bone mineral disease by comparing kidney-transplanted pediatric patients with pediatric patients on dialysis, and to determine the appropriate marker in the diagnosis and monitoring of renal osteodystrophy by examining the relationship between osteoprotegerin and fibroblast growth factor 23 and renal osteodystrophy. Method: This study was conducted between 2019 and 2020 in the Department of Pediatric Nephrology at Istanbul Medical Faculty, Istanbul University. Study was conducted on patients between the ages of 0-18 who were followed up with a diagnosis of chronic kidney disease and received dialysis treatment, and the children who had a kidney transplant more than 6 months ago. 31 kidney-transplanted patients and 25 patients receiving dialysis treatment were included in the study. Anthropometric measurements, measurements of parathyroid hormone, alkaline phosphatase, calcium, phosphorus, 25-hydroxy vitamin D, blood gas parameters, hemoglobin, lipid profile, vitamin levels, bone mineral density and echocardiography, eye examination, blood pressure measurement data were recorded from the patients' files. Fibroblast growth factor 23 and osteoprotegerin serum levels of patients were measured. Serum levels were measured with commercial kits provided by Elabscience (Texas, USA; catalog no: E-EL-H1116) based on the Sandwich ELISA principle. While evaluating the study data, in addition to descriptive statistical methods, the distribution of the data was evaluated with the Shapiro-Wilk Test. The Kruskall-Wallis test was used to compare three or more groups which did not show normal distribution. ANOVA test was used in normally distributed groups. Mann-Whitney U Test was used to compare two groups that did not show normal distribution, and Student t test was used to compare two normally distributed groups. Chi-square and Spearman's correlation analysis were used to determine the relationship among the quantitative data and qualitative data, respectively. Patients were evaluated in groups according to dialysis status, primary renal disease type and disease onset age. In addition, kidney-transplanted patients were divided into subgroups according to the presence of rejection. Dialysis patients were divided into subgroups according to dialysis modality and re-evaluated. Results: The average ages of the kidney-transplanted patients and dialysis patients were 14,16±3,93 and 12,81±5,17 years, respectively. While 44.6% (n=25) of the patients were female, 55.4% (n=31) were male. While 96% of the dialysis patients had high PTH value; 54.8% of the kidney-transplanted patients who did not receive dialysis had a high PTH value. The lower height SDS, body weight SDS and BMI SDS values of the group receiving dialysis was statistically significant (respectively p=0,001; p<0,01; p=0,001; p<0,01 and p=0,022; p<0,05). 58.9% of the patients had a height SDS value of -2 or below, and 66.6% of these patients had 25-OH vitamin D deficiency, 9.1% of the patients had folate deficiency, and 27.3% of the patients had vitamin B12 deficiency. It has been shown that 17% of the patients have osteoporosis and 27.7% have osteopenia. While a significant negative correlation was found between alkaline phosphate value and BMD value of bone mineral density measurement (r=-,525, p<0,01), there was no correlation between both BMD and Z score and PTH. It was statistically significant that the bone mineral density BMD value of the group receiving dialysis was found to be lower than the group who did not receive (p=0,025; p<0,05). There was a negative relationship between glomerular filtration rate and parathyroid hormone value (r=-,373, p<0,01). There was no correlation between FGF-23 value and GFR, PTH, ALP, phosphorus, osteoprotegerin levels (p>0,05). A positive correlation was found between osteoprotegerin and bone mineral density measurement BMD value and height SDS value in the dialysis group (r=,518, p<0,05 and r=,599, p<0,01). Conclusion: The improvement on the renal osteodystrophy symptoms in kidney-transplanted patients has shown that early renal transplantation has a protective role for bone mineral disease. The positive correlation of osteoprotegerin levels with BMD value and height SDS value suggests that OPG has protective effect for osteoporosis. Additional studies are needed to identify sensitive markers in the monitoring of renal osteodystrophy and to use these indicators to monitor the patients and the response received to treatment. Key words: Pediatric kidney transplantation, renal osteodystrophy, osteoprotegerin, fibroblast growth factor 23