Abstract
BackgroundHyperphosphataemia in dialysis subjects is associated with increased mortality. However cause and effect has not been proven, and the ideal phosphate target range is unknown despite KDOQI’s call for studies over 12 years ago. The design and conduct of a randomized controlled trial is challenging because maintaining two groups within differing target ranges of serum phosphate has not been achieved over a long follow-up of 1 year, in a trial setting, before. The SPIRiT study examines the subject acceptance, recruitment and retention rates for such a study in which subjects were randomised to two distinct serum phosphate concentrations, then titrated and maintained over 12 months.MethodsA two center trial of 104 hemodialysis subjects randomized to lower range LRG 0.8–1.4 mmol/L or 2.5–4.3 mg/dL) and higher range (HRG 1.8–2.4 mmol/L or 5.6–7.4 mg/dL) serum phosphate groups. Two months’ titration and ten months’ maintenance phase. Interventions were non-calcium phosphate binders, self-help questionnaires, with blood tests at specified time intervals.ResultsThirteen percent of the eligible dialysis population were successfully recruited. A mean separation by serum phosphate of 1.1 mg/dL was achieved and maintained between the groups over 10 months. Drop-out rate was 27% with mortality 10%. Nine subjects in the HRG (17.6%) and two subjects in the LRG (3.8%) died during the study, however the study was not powered to detect significant differences in outcomes.ConclusionRandomizing dialysis subjects to separate treatment targets for serum phosphate can achieve a clinically significant sustained separation over 12 months. A large scale longer term study is required to examine outcomes including mortality.Trial registrationThe trial registration number is ISRCTN24741445 – Date of registration 16th January, retrospectively registered.
Highlights
Hyperphosphataemia in dialysis subjects is associated with increased mortality
No stratification for known risk factors was employed because of the small numbers randomised, with the result that the Lower Range Group (LRG) were 5 years older but had 0.5 years less dialysis vintage compared to the Higher Range Group (HRG)
The HRG had a higher percentage of subjects with diabetes (29.4% versus 20.8%), coronary artery disease (29.4% versus 18.9%) and vascular disease (31.4% versus 22.6%) compared to the LRG
Summary
Hyperphosphataemia in dialysis subjects is associated with increased mortality. cause and effect has not been proven, and the ideal phosphate target range is unknown despite KDOQI’s call for studies over 12 years ago. The design and conduct of a randomized controlled trial is challenging because maintaining two groups within differing target ranges of serum phosphate has not been achieved over a long follow-up of 1 year, in a trial setting, before. Large observational studies have identified hyperphosphatemia as an independent risk factor for cardiovascular disease and mortality in dialysis patients [1,2,3]. Such studies cannot establish causality, but current guidelines encourage careful control of serum phosphate in the uncertain expectation that it will improve outcomes. Initial screening involved all patients from the two adult renal services of Greater Manchester in England, a conurbation with a total population of 2.8 million people
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