Dialysate magnesium, hypomagnesaemia and under-nutrition in CAPD

T Bellwood, C Dick, S Doyle, K Farrington

Lister Hospital, Stevenage

Problem. Plasma magnesium levels are often elevated in patients with end-stage renal failure (ESRF) and many patients dialyse using dialysis fluid with low magnesium levels. We noticed hypomagnesaemia (< 0.74 mmol/l) in a number of our CAPD population and investigated its associations

Purpose. To investigate the relationship between hypomagnesaemia and other routinely measured parameters reflecting dialysis adequacy and nutrition in CAPD patients receiving dialysis with a standard dialysis fluid containing low magnesium concentrations (0.25 mmol/l: PD4).

Design: This was a cross-sectional study carried out in all our CAPD patients who had received treatment with a low magnesium dialysis fluid for at least 3 months.

Findings. 58 patients were studied of whom 12 were hypomagnesaemic (20.7%). Hypomagnesaemic patients had been dialysed for longer (48.5 vs 27.9 months: p = 0.034), had significantly lower levels of blood urea (15.5 vs 19.4 mmol/l: p = 0.029), serum sodium (134.7 vs 138.9 mmol/l: p < 0.001), serum potassium (4.1 vs 4.5 mmol/l: p = 0.044), serum phosphate (1.33 vs 1.65 mmol/l: p = 0.012), serum albumin (27.5 vs 30.4 g/l: p = 0.052), normalized protein catabolic rate (0.71 vs 0.84: p = 0.048). In addition a greater proportion had been referred for dietetic advice during the previous 3 months ( p = 0.001) and were receiving dietary supplements (p = 0.014). there was no difference between hypomagnesaemic patients and other with respect to Age ,sex, incidence of diabetes, weight change in preceding 3 months, BMI, serum cholesterol, serum calcium, PTH, CRP, total or renal Kt/V.

Conclusion. Hypomagnesaemia is common in CAPD patients receiving dialysis with a standard dialysis fluid containing low magnesium concentrations and is associated with indices of undernutrition. The lack of association with BMI or recent weight change, together with the association with hyponatraemia suggests that there is water retention in these patients.