Table 2.

Bone Biomarkers used in Clinical Practice

Biomarker	Sample collection and Assay	Predictor of histomorphometry	Predictor of Fractures
PTH	Multiple assays and poor standardization between the various assays. High diurnal variation. Levels vary with temperature of plasma specimen. PTH assays detects variable amounts of circulating C terminal fragments. Some fragments are potentially biologically active. Co-efficient of variation within subject in hemodialysis patientsis 25.6%(64)	PTH levels higher with increased bone turnover than those with adynamic bone disease in CKD 3–5 (65)as well as CKD 5D(66).* No consistent relationship between PTH and bone formation rates or bone volume(67) Racial differences(68)	Inconsistent results for risk stratification between high or low PTH and fractures(69–71) Decreased fracture risk after parathyroidectomy(7 2)
Bone Specific Alkaline Phosphatase b-alp)	Co-efficient of variation within subject in hemodialysis patients is 12.5%(73) Assay not widely available clinically Cross reactivity of assay with the liver-derived alkaline phosphate fraction	b-alp levels are higher with higher bone turnover in CKD 5D(23, 74)* No relationship of b-alp with bone volume (23, 75)	No prospective data on b-alp and risk of fractures in CKD Higher risk of fractures in CKD 5D with high total alkaline phosphatase levels (76).

^*PTH measured by the intact assay (Elecsys PTH 91–84) assay, Roche Diagnostics corporation, Indianapolis, IN, USA) was equally predictive to bone-specific alkaline phosphatase (BAP) of underlying bone turnover with a sensitivity of 0.58 vs 0.403, a positive predictive value of 0.373 vs 0.287, and a negative predictive value of 0.903 vs 0.877 (PTH vs BAP, respectively) for the detection of increased bone formation rates. The two together did not improve sensitivity or specificity (46).