CYP27A1 and chronic kidney disease: BSAP lacks a readily available automated assay, and there are concerns of cross‐reactivity with the liver iso‐enzyme,129 there are no validated reference ranges of BTMs in patients with CKD and ESKD, many BTMs are cleared by the kidney (monomeric P1NP, osteocalcin, and CTX) and BTMs have high intra‐ and interassay variability and biological variability.130