Effect of change in renal replacement therapy modality on laboratory variables: a cohort study from the UK Renal Registry.
BACKGROUND
Although previous comparisons have shown differences in biochemical and haematological variables between patients on haemodialysis and peritoneal dialysis and those with functioning transplants, these could be due to case mix rather than being due to differences in the types of renal replacement therapy (RRT). The longitudinal follow-up of individual patients after the change in modality has not hitherto been described.


METHODS
From the UK Renal Registry (UKRR) database of patients receiving RRT between 1 January 1997 and 31 December 2004, we identified two cohorts: 2033 patients who had been on either haemodialysis (HD) or peritoneal dialysis (PD) for at least a year and who subsequently underwent transplantation and then survived at least a year (PD + HD to Tp); and 892 patients who had been on PD for at least a year who changed to HD and then survived at least a year (PD to HD). In both cohorts, the following variables were studied for the four quarters before and after the change of modality: blood haemoglobin and serum, ferritin, albumin, bicarbonate, cholesterol, calcium, phosphate and parathyroid hormone (PTH) concentrations. No information on drug treatment was available.


RESULTS
In the PD + HD to Tp cohort, transplantation was associated with a rise in haemoglobin, albumin and bicarbonate, a fall in ferritin and phosphate, no change in calcium, a fall (but not to normal) in PTH and a transient rise in cholesterol concentrations. In the PD to HD group, the change in modality was associated with a significant temporary fall in haemoglobin, a progressive rise in ferritin, albumin, phosphate and PTH, no change in calcium and fall in bicarbonate and cholesterol concentrations.


CONCLUSION
The change from HD to PD is associated with a significant fall in the haemoglobin concentration; anticipation of this change might enable clinicians to ameliorate it. Persistent hyperparathyroidism is common after kidney transplantation.