Measurement of Parathormone in Chronic Kidney Disease: An Easy Task?

PTH determination is routinely used in Nephrology as a surrogate marker for the diagnostic and follow-up of Chronic Kidney Disease Mineral and Bone Disorders (CKD-MBD). Nevertheless, this determination is far from an easy task. Indeed, this peptide circulates as a mixture of active PTH (1-84) and multiple fragments that accumulate in CKD and interfere, with different percentages of crossreactivity, with the different kits of PTH present on the market. This has lead to very important differences in the values obtained with these kits. Unfortunately, this point had not been taken into account in the former KDIGO Guidelines that asked to maintain the PTH levels of the hemodialyzed patients between 150 and 300 pg/mL, whatever the kit. The KDIGO Guideline, in 2009, overcame this problem by asking to maintain the patients between 2 and 9 times of the upper reference range of the Laboratory. But there comes the problem of the establishment of a reference range for PTH. Indeed, for such a purpose, one should exclude any patient presenting causes of secondary hyperparathyroidism - and thus exclude patients suffering from vitamin D deficiency - which was not done by most of the Manufacturers. Thus, the upper reference range generally proposed in the inserts of the kits is generally much higher that could be expected. Finally, different interferences have been demonstrated in PTH determination and the stability of the peptide may vary according to the sample type (plasma EDTA or serum) or even with different assays. PTH measurement in patients with CKD may thus appear as an easy task as numerous automated assays are now available, but, in practice, its interpretation is not so obvious. In this Chapter, we will review the various aspects concerning the measurement of PTH in patients with CKD and especially in dialysis patients all the more that, during the past 10 years, new PTH assays became available, and new concepts concerning PTH reference values have emerged.

Keywords: Parathormone, calcium, reference value