Clotting in dialyzers due to low pH of dialysis fluid

During November and December 1975 frequent clotting occurred in the extracorporeal circuits of different dialyzers used in our unit. After installation of new automatically regenerating ion exchange resin columns,, the pH of deionized water ranged from 4.2 to 8.4 during 24 hr periods. Dialysate pH ranged between 5.3 and 8.2, and the patient's whole blood pHs ranged from 7.15 to 7.4 at the dialyzer inlet and from 6.2 (!) to 7.4 at the outlet. A strong correlation was seen between the acidity of the water and the frequency of clotting, and it was considered possible that the clotting was due to structural changes within the heparin molecules induced by the low pH. Following the introduction of an automatic titration device into our dialyzate preparation system, clotting with consecutive blood loss and subjective clinical symptoms have disappeared.