Purpose: 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.
Methods: 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%.
Results: 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.
Conclusion: 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 μg/L), the [Al]d should therefore not exceed 4 μg/L. At the level presently supported by K/DOQI ([Al]d < 10 μg/L), [Al]p could realistically reach 50 μg/L and potentially cause toxicity.