Haemoglobin concentration and serum erythropoietin in renal dialysis and transplant patients.

In patients with chronic renal failure the use of the relatively new dialysis technique of continuous ambulatory peritoneal dialysis (CAPD), unlike other forms of dialysis, is consistently associated with an increase in Hb concentration, but the mechanism remains obscure. We measured Hb, haematocrit, S-erythropoietin and Hb-oxygen affinity in 3 groups of patients with chronic renal failure. (1) Untreated patients starting on haemodialysis. (2) Patients on intermittent peritoneal dialysis changing to CAPD. (3) Patients from the above 2 groups receiving renal transplants. In addition, red cell mass, plasma volume and red cell survival were measured in (2), before starting CAPD and at 6 months. There were distinctly different patterns of change in Hb concentration, Hb-oxygen affinity and S-erythropoietin in the 3 groups of patients. The increase in Hb concentration with CAPD is due to both a fall in plasma volume and an increase in red cell mass, with an increase in red cell survival. There was no change in Hb-oxygen affinity or serum erythropoietin concentration. The improvement in red cell mass and survival may be related to increased clearances of substances with mol. wt.s between 500 and 5000 daltons which accumulate in renal failure (uraemic middle molecules).