Aluminum transfer during dialysis: a systematic review

Dialysis-dependent patients are particularly susceptible to the toxic effects of aluminum (Al) because of their impaired ability to eliminate it. Al contamination of dialysis fluid remains a threat in this population. The mechanism for Al diffusion across dialysis membranes is not well established. Our objective is to verify, in AL-exposed patients, the postulate that the direction of Al transfer is predicted by the concentration gradient between free diffusible plasma Al and dialysate Al. A systematic review of the literature was performed. Only papers which included Al plasma concentration ([Al]p), Al dialysate concentration ([Al]d) and direction of Al transfer (positive = from dialysate to plasma, negative = from plasma to dialysate) were selected. We also included four patients from our own cohort. Assuming that [Al]p has an ultrafiltrable fraction between 17 and 23 %, cases were considered in keeping with our hypothesis if any of the following scenarios was present: negative Al transfer when [Al]d < [Al]p*23 % and positive Al transfer when [Al]d > [Al]p*17 %. The search yielded 409 articles, of which 12 were selected for review. When reviewing individual patients for analysis, 108 out of 115 (94 %) patients followed our hypothesis. By further excluding cases in which Al transfer could not be determined, only three out of 111 patients were contrary to out hypothesis. Comparing ultrafiltrable Al to dialysate Al permits to accurately predict the direction of Al transfer. The optimal [Al]d should be < 20 % of the maximally acceptable [Al]p. In order to follow K/DOQI guidelines ([Al]p < 20 mu g/L), the [Al]d should therefore not exceed 4 mu g/L. At the level presently supported by K/DOQI ([Al]d < 10 mu g/L), [Al]p could realistically reach 50 mu g/L and potentially cause toxicity.