Serum Markers of Low-Turnover Bone Disease in Mexican Children with Chronic Kidney Disease Undergoing Dialysis

Abstract

The frequency of low-turnover bone disease (LTBD) in patients with chronic kidney disease (CKD) has increased in past years. This change is important because LTBD is associated with bone pain, growth delay, and higher risk for bone fractures and extraosseous calcifications. LTBD is a histological diagnosis. However, serum markers such as parathyroid hormone (PTH) and calcium levels offer a noninvasive alternative for diagnosing these patients. To describe the prevalence of LTBD in pediatric patients with renal failure undergoing some form of renal replacement therapy, using serum calcium and intact PTH levels as serum markers. In this cross-sectional study, 41 children with CKD undergoing dialysis treatment (31 on continuous ambulatory peritoneal dialysis and 10 on hemodialysis) were included. There were no inclusion restrictions with respect to gender, cause of CKD, or dialysis modality. The children were studied as outpatients. The demographic data, CKD course, time on dialysis, phosphate-binding agents, and calcitriol prescription were registered, as well as weight, height, Z-score for height, linear growth rate, and Z-score for body mass index. Serum calcium, phosphorus, aluminum, PTH, alkaline phosphatase, osteocalcin, glucose, creatinine, urea, cholesterol, and triglycerides were measured. There were 20 (48.8%) children with both PTH < 150 pg/mL and corrected total calcium >10 mg/dL who were classified as having LTBD[(+)]; the remaining 21 (51.2%) children were classified as having no LTBD[(-)]. The LTBD(+) patients were younger (11.2 +/- 2.7 vs 13.2 +/- 2.4 years, p < 0.01) but they had no differences regarding Z-scores for height. Linear growth in 6 months was less than expected in both groups (-0.15 +/- 0.23 cm/month), but the difference between expected and observed growth was higher in the LTBD(+) group (-0.24 +/- 0.14 vs -0.07 +/- 0.28 cm/mo, p < 0.03). LTBD(+) patients also had lower serum creatinine (8.69 +/- 2.75 vs 11.19 +/- 3.17 mg/dL, p < 0.01), higher serum aluminum levels [median (range) 38.4 (9 - 106) vs 28.1 (9 - 62) microLg/L, p < 0.05], and lower systolic blood pressure (112.0 +/- 10.3 vs 125.0 +/-1 2.9 mmHg, p < 0.015) and diastolic blood pressure (76.0 +/- 9.7 vs 84.5 +/- 8.2 mmHg, p < 0.017). A significant correlation was found between PTH and alkaline phosphatase (r = 0.68, p < 0.001), but not between PTH and aluminum. The LTBD(+) biochemical profile was found in 48.8% of the children and was associated with impaired linear growth. Aluminum contamination, evidenced by higher serum aluminum levels, may have had a pathogenic role in these disorders. Higher systolic and diastolic blood pressure levels may be related to higher serum PTH levels.