This study evaluated the potential of the Personal Dialysis Capacity (PDC) test to discriminate fast transport status (FTS) as a consequence of inflammation versus FTS because of other causes. This distinction is important because new therapeutic options such as icodextrin and automated peritoneal dialysis can abolish the negative impact on outcome of FTS if fast transport is not caused by inflammation. A PDC test and a Peritoneal Equilibration Test (PET) were performed in 135 incident PD patients. Membrane characteristics were related with baseline biochemical parameters and C-reactive protein. After correction for other covariates, only large pore flux (J(v)L) but not surface area over diffusion distance (A0/dX) or dialysate over plasma concentration was related to C-reactive protein. Using the PDC test for detection of inflammation, positive and negative predictive values were 16/36 and 80/99, respectively, whereas with PET, positive predictive value was 5/20 and negative predictive value 92/115 (chi2 = 0.009). In a Cox regression for patient survival with correction for age, a J(v)L higher than expected by the surface area over diffusion distance, predicted outcome (P = 0.04). Patients with inflammation had a higher J(v)L (0.21 +/- 0.12 versus 0.17 +/- 0.09; P = 0.06) and a lower ultrafiltration (89 +/- 631 versus 386 +/- 601 ml/d; P = 0.06) and urine output (878.45 +/- 533.55 versus 1322 +/- 822 ml/d; P = 0.023) than patients without inflammation. There was no difference for surface area over diffusion distance (A0/dX) or dialysate over plasma concentration. A PDC test yields far more information about the peritoneal membrane characteristics than a PET. A J(v)L higher than expected by the A0/dX is an indicator of inflammation and is related to an increased mortality. The PET is not able to discriminate between FTS because of inflammation versus because of anatomic reasons, whereas the PDC test does.