Variability of Serum Concentration of Calcium, Phosphate and Parathyroid Hormone Depending on Time of Blood Draw for Patients on Nocturnal Home Hemodialysis

Background: Guidelines for patients treated with conventional hemodialysis patients have been written for target serum levels for calcium (Ca), phosphate (PO4) and intact parathyroid hormone (iPTH). No guidelines exist for nocturnal home hemodialysis (NHHD) patients for target values or timing of the blood sample draw. We undertook a prospective cohort study to examine the variability in pre, post and clinic (post-post) serum values for Ca, PO4, and iPTH in NHHD patients to determine if timing of blood draw could affect clinical decisions. Methods: Twenty prevalent NHHD patients collected blood pre and post their usual NHHD session with an additional blood sample drawn in clinic (postpost). Median and interquartile range of pre, post and clinic (post-post) values of iPTH, PO4 and Ca were calculated and compared with Freidman/Wilcoxon test. Serum concentrations were also categorized according to Canadian Society of Nephrology (CSN) guidelines target values for pre and clinic (post-post) samples. The proportion of patients that would be categorized differently by clinic (post-post) samples was determined. Results: There was a significant difference between pre-serum values compared to post and clinic (post-post) values. Overall, iPTH, PO4 and Ca values would be misclassified in 25%, 70% and 50%, respectively if blood was drawn at the clinic visit (post-post) compared to pre-HD as per CSN guidelines. Conclusions: Although no specific guideline has been written for NHHD patients, to ensure consistency of management compared to in-centre HD patients, lab values should be drawn pre-HD until clinical evidence suggests that the recommendations should be different for NHHD.