Postdialysis serum phosphate equilibrium in hemodialysis patients on a controlled diet and no binders

Abstract

Background: Studies evaluating the change in serum phosphate post hemodialysis (HD) demonstrate an initial decline during dialysis but a rebound post dialysis. However, previous studies were done on usual diet and phosphate binders, with limited number of blood draws, confounding conclusions. We determined serum phosphate reduction, rebound, and equilibrium over 48 h in HD patients consuming a controlled, low phosphorus diet without binders.Methods: Serum phosphate (mg/dL) was analyzed before and after a HD treatment and frequently during the ensuing 48 h intradialytic period in the clinical research unit. Thirteen subjects were enrolled and had been off phosphate binders for 10 days and consumed a standardized low phosphate (900 mg/day) diet for 3 weeks prior to the assessments. Linear regression was used to determine relationships between the pre-HD serum phosphate, decline post-HD (post-HD drop); and a 48 h area under curve (AUC) using the trapezoidal method as a measure of overall phosphate levels from the end of dialysis to 48 h post dialysis. Repeated Measures ANOVA with Dunnett's posthoc test was used to determine rebound. Results: Five of 13 subjects returned to >90% of their pre-HD serum phosphate within the first 24 h post-HD, and serum phosphate was 94 AE 0.11% (range 63%-113%) by 48 h after the completion of HD. The 48 h AUC of serum phosphate during the interdialytic period was correlated with both pre dialysis phosphorus (r = 0.85; p = 0.0002) and the pre-post drop in serum phosphate during dialysis (r = 0.69; p = 0.0085). In contrast, the net ultrafiltration was not related to the 48 h AUC of serum phosphorus (r = 0.20; p = 0.51). Conclusions: In hemodialysis patients on standard low phosphorus diet and no phosphate binders, the interdialytic serum phosphorus level, assessed as AUC, is determined by the pre dialysis phosphorus and net-change in serum phosphorus during the dialysis treatment, but not the ultrafiltration volume [Correction added on 25 January, after first online publication: In the last sentence of the Abstract, the word "potassium" has been replaced with "phosphorus" to improve accuracy.].

Phosphate balance during dialysis and after kidney transplantation in patients with chronic kidney disease

“…The current belief that phosphate returns to the basal level a few hours after dialysis was not confirmed in a recent study of haemodialysis patients on a low-phosphate diet with no binders [39]. In that study, phosphate returned to basal levels within the first 24 h after dialysis in less than 40% of the individuals.…”

“…An evaluation of 455 dialysis sessions showed that at least 38 h of dialysis weekly are required to maintain normal phosphate levels in patients with a phosphate intake of 0.7 g/ day not treated with binders [37]. The predialysis serum phosphate concentration also influences phosphate removal [38], and restricting dietary phosphate may blunt postdialysis rebound [39]. Hemodiafiltration has been shown to remove higher amounts of phosphate in patients with predialysis levels below 7 mg/dl [40].…”

Association Between Disturbed Serum Phosphorus Levels and QT Interval Prolongation

“… 33 Recent investigation of the rebound increment of serum P after HD revealed that the low serum P levels increased slightly just after the session, and remained plateaued at this level for the following 3 to 4 hours, with no additional increase. 47 Although it is not clear to what extent this transient hypophosphatemia affects QT interval through adenosine triphosphate deficiency in the myocardium, it is clear that fatal arrhythmias often occur within 12 hours after an HD session. 48 We believe that hypophosphatemia after HD could be responsible for the present results.…”