Quarterly 7ournal of Studies On

SIR,-We read with interest the paper of Dr. P. Kramer and others (6 May, p. 320) and while we agree that the decrease in efficiency with re-use may be the result of "blood deposits on the membrane surface inhibiting exchange," we feel there are two points which must be made. Firstly, the aurhors say that of the dialysers studied, the Ab-Gambro dialyser had the greatest blood loss due to "blood pooling and clotting on the surface of the membrane" and yet they found the mean blood loss in this dialyser to be only 6-86 ml. This was compared with blood losses of 3 65 ml and 3-48 ml for the Rhone-Poulenc and the Kiil dialysers respectively. Surely an increase of blood loss by some 3 ml cannot interfere with dialyser performance? We feel that this discrepancy is exnlained by the fact that Dr. Kramer and his colleagues measured the blood losses by the technique of haemoglobinometry on a saline "washthrough" (although they do not give any details of their methodology). This technique is subject to considerable inaccuracies,' and, furthermore, it will underestimate blood loss should blood be retained on the membrane surface as adherent thromnbus. We have studied in detail these and other dialysers, and have found that thrombus formation takes place upon the membranes of the Ab-Gambro dialvser in spite of adequate heparinization. This, in turn, will cause a high blood loss; using an accurate technique, involving 5"Cr labelled red blood cells, we h,ave found this to be 36 ml ± 4 (M ± S.D.) (unpublished data). The second point to be made is that the Ab-Gambro dialvser in question was the Gambro-Alwall which we have found to have characteristics which encourage the in vivo formation of thrombus (unpublished data). We are currently engaged in assessing the new Gambro-Lundia dialyser, and can report that this does not have such characteristics and its use is associated with a very low blood loss (4 0 ± 1-7 ml). It is unlikely, therefore, that blood deposits will affect the efficiency of this dialyser.-We are, etc.,