CHAPTER 34 – Variability in the Measurement of Biochemical Markers of Bone Turnover

This chapter deals with issues of variability. It reviews the sources of variability and presents a number of statistical models to estimate the variability and characterize the change in bone turnover markers in an individual patient. Variability in the measurement of chemical analytes is a major issue in clinical chemistry. Numerous factors influence bone turnover, but there are even more sources of variability that need to be taken into account when measuring bone turnover with biochemical markers. To minimize some of the limitations linked to preanalytical and analytical variability, standardized sampling and sample handling are mandatory to obtain reliable results. Controllable factors such as the mode of sample collection, samples handling and storage, diurnal and menstrual rhythms, presampling exercise, and presampling diet should be taken care of wherever possible. Laboratories are encouraged to establish their own reference ranges and to use gender and age-specific reference intervals. To further reduce variability, standardization of bone marker assays and routine proficiency testing programs are strongly recommended.