In this pilot study the investigator will examine the levels of fibroblast growth factor (FGF-23) and parathyroid hormone (PTH) levels during hemodialysis therapy in 30 patients and assess the correlation between these parameters and the T-50 calcification propensity, as well as further parameters of secondary hyperparathyroidism (sHPT), like serum calcium (sCa), phosphate (P), 25-hydroxy-vitamin D (25(OH)D) and 1,25 dihydroxy-vitamin D (1,25(OH)2D).

The investigator hypothesize that FGF-23 and PTH levels are at their highest at the beginning of dialysis and decrease during the treatment.

Background: The development of sHPT in hemodialysis patients is a common complication which induces an increase in calcification and atherosclerosis. Elevated FGF-23 levels are already found in early stages of chronic kidney disease (CKD) and it has been shown that high FGF-23 levels are associated with the development of cardiovascular disease and increased overall mortality.

Method: In this pilot study a total number of 30 patients on maintenance haemodialysis will be enrolled. The investigator will examine the course of FGF-23 and PTH levels during a single hemodialysis session. In addition, the T-50 time, a novel non-traditional cardiovascular risk factor as well as further parameters of sHPT, such as serum calcium (sCa), phosphate (P), 25-hydroxy-vitamin D (25(OH)D) and 1,25 dihydroxy-vitamin D (1,25(OH)2D) will be assessed.

Hypothesis and specific aims: The major end point of the study is the level of FGF-23 and PTH at three points during hemodialysis treatment. As secondary end points the T-50 calcification propensity and further parameters of sHPT, as well as the correlation between these parameters will be measured.

Hemodialysis is classified as a kidney replacement therapy and FGF-23 and PTH are partly metabolized and excreted by the kidneys. Based on this the investigator hypothesize that FGF-23 and PTH levels are at their highest at the beginning of dialysis and decrease during the treatment.

Inclusion Criteria:

• >18 years
• hemodialysis three times a week

Exclusion Criteria:

• Subject is currently enrolled or not yet completed at least 30 days since ending other investigational device or drug trial(s), or is receiving other investigational agent(s)
• Pregnancy
• Subject has any kind of disorder that compromises the ability of the subject to give written informed consent and/or to comply with the study procedures

30 adult patients with chronic kidney disease receiving hemodialysis treatment at the Medical University of Vienna, Department of Internal Medicine III, Division of Nephrology and Dialysis. All patients are on a thrice-weekly dialysis schedule.