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Phosphorus Control
Phosphate Control in Renal Disease
a report by
Fouad Albaaj
1
and Alastair J Hutchison
2
1. Consultant Nephrologist, Queen Elizabeth and City Hospitals, Birmingham; 2. Consultant Nephrologist and
Clinical Director, Renal Unit, Manchester Royal Infirmary
Hyperphosphataemia is prevalent among chronic renal failure and dialysis absorption from a mixed diet has been reported to be in the range of
patients. It is known to stimulate parathyroid hormone and suppress 55–70% in adults. However, the intestinal absorption of phosphate is
vitamin D
3
production, thereby inducing parathyroid bone disease. greatest in the jejunum and decreases along the length of the small
Furthermore, it may independently contribute to cardiac causes of death intestine. Decreasing dietary phosphate is difficult to achieve without
through increased myocardial calcification and enhanced vascular significant reduction in protein intake, which may put patients with renal
calcification. Therefore, phosphate control is now recognised to be of failure at risk of malnutrition.
2
prime importance in the management of patients with chronic kidney
disease (CKD). Dialytic Phosphate Removal
On average, only 500–1,000mg of phosphate are eliminated by one
It is important to control phosphate levels early in the course of CKD in dialysis treatment. The best results are obtained with the use of large-
order to avoid and treat secondary hyperparathyroidism and to minimise surface-area dialysers with prolonged dialysis times and high blood-flow
risks of cardiovascular and soft tissue calcifications. Because of its large rates. In peritoneal dialysis, the weekly removal of phosphate has been
sphere of hydration and complex kinetics of phosphate elimination, estimated at around 2,200mg, but this depends on the distribution of
phosphate is not easily removed by dialysis. Although long hours or slow
nocturnal dialysis may be much more effective in controlling serum
phosphate levels, these techniques carry with them significant logistical
difficulties and are not generally applicable to all patients. Long-term
…phosphate control is now recognised
dietetic restrictions are often difficult to follow and therefore oral
phosphate-binding agents are required in the majority of patients.
to be of prime importance in the
management of patients with chronic
Treatment of Hyperphosphataemia
kidney disease.
Dietary Intervention
Major sources of dietary phosphate include milk and cheese, eggs, meat
(particularly liver, kidney and veal), fish (particularly fatty fish – such as isotonic and hypertonic peritoneal dialysis fluids.
3
Haemofiltration or
salmon – and shellfish), peas, beans, lentils, soya products, bran and all haemodialfiltration seem to be somewhat more effective than
bran-containing cereals, as well as other coarse-grain foods such as conventional haemodialysis, probably because of the continuous nature
oatcakes. Processed foods usually contain significantly more phosphate of these treatments.
4
Kinetic studies of haemodialysis have shown that
than do natural products. The mean intake of phosphate in the UK diet serum phosphate levels drop rapidly in the first 1–2 hours of treatment
is 1,260mg/day from food and 4.4mg/day from drinking water.
1
The net and then reach a plateau. The amount of phosphate removed decreases
significantly in the second half of dialysis. Serum phosphate levels then
rise relatively quickly in the first few hours after termination of dialysis –
Fouad Albaaj is a Consultant Nephrologist at Queen the so-called ‘rebound phenomenon’.
5
However, lengthening dialysis or
Elizabeth and City Hospitals in Birmingham. His clinical and
using larger dialysers with higher efficacy enhances phosphate removal;
research interests lie in the area of divalent ion metabolism
in chronic renal failure and renal osteodystrophy.
this was demonstrated by the Tassin Centre (Paris, France) experience
6
and by Kooisera and colleagues in The Netherlands.
7
The results were
E: falbaajfab@hotmail.com
most marked in the nocturnal haemodialysis schedule: serum phosphate
levels were considerably lower with nocturnal haemodialysis, and patients
increased their dietary phosphate intake by 50% and did not require
Alastair J Hutchison is a Consultant Nephrologist and
phosphate binders after the fourth month.
Clinical Director of the Renal Unit at Manchester Royal
Infirmary. He has clinical and research interests in renal bone
disease and osteoporosis in patients who are on dialysis or Reduced-calcium Dialysate
have received a renal transplant, and has published
Reduction of the calcium concentration in dialysis fluids has been shown
approximately 70 scientific papers and book chapters in
these fields. Dr Hutchison is a reviewer and referee for a
to reduce hyperphosphataemia without deleterious effects on bone
variety of international journals, including Nephrology,
histology in haemodialysis patients.
8
Three independent studies
Dialysis and Transplantation and Kidney International.
demonstrated these effects in continuous ambulatory peritoneal dialysis
(CAPD) patients using fluids with a calcium concentration of 1.25mmol/l
30 © TOUCH BRIEFINGS 2007
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