Serum Angiotensin-Converting Enzyme as a Marker of Dialyzer Membrane Biocompatibility?

Dr. B.K. Krämer, Medizinische Universitätsklinik, Otfried-Müller-Strasse 10, D-7400 Tübingen (FRG) Sir, We have read with interest the recent letters of Maher et al. [1] and Docci et al. [2]. Both authors suggest that serum angiotensin-converting enzyme is not a useful marker of dialysis membrane biocompatibility, in contrast to earlier findings of Nielsen et al. [3]. 16 patients on maintenance haemodialysis for 2–186 months were studied during haemodialysis with cupro-phane and non-cuprophane membranes [4]. Serum angiotensin-converting enzyme decreased slightly during haemodialysis, independent of the dialyzer membrane used. In addition, serum angiotensin-converting enzyme levels were nearly identical during use of a cuprophane and a non-cuprophane dialyzer membrane (82.3 ± 3.9 U/min/1 vs. 82.6 ± 3.3 U/min/1; range of normal values 18–40 U/min/1, corrected for haemoconcentration) [4]. Serum angiotensin-converting enzyme levels were compared with duration of maintenance haemodialysis in 23 patients (duration of maintenance haemodialysis from 2 to 216 months; age 34–78 years; etiology of renal failure: glomerulonephritis (n = 6), diabetic nephropathy (n = 5), polycystic kidney disease (n = 3), pyelonephritis (n = 2), hypertension (n = l), multiple myeloma (n = l), renal artery stenosis (n = 1), unknown (n = 4)). No significant correlation between serum angiotensin-converting enzyme and duration of maintenance haemodialysis was demonstrable (fig. 1). Our results imply that serum angiotensin-converting enzyme cannot be used as an indicator of dialyzer membrane biocompatibility and are in accordance with the results of other investigators [1, 2, 5–7]. Elevated serum angiotensin-converting enzyme levels in haemodialysis patients have also been demonstrated by several investigators [5, 6, 8–10], but have not been confirmed by others [1–3, 7, 11]. In contrast to our results, most authors were not able to demonstrate a change in serum angiotensin-