Three consecutive day collection of dialysate and urine to identify non-compliance in CAPD patients

Compliance with dialysis prescription is all important determinant of adequacy of CAPD. Several reports have suggested that non-compliance may be detected by a high creatinine excretion ratio (CrEx ratio = measured creatinine excretion in a 24-h collection of urine and dialysate/predicted creatinine excretion) and that it occurs in a substantial proportion of patients. However the validity of this screening method to identify non-compliant patients has been questioned, mostly because of the interindividual variation of creatinine excretion in a CAPD population.

Whenever possible we performed a 3-day collection of dialysate and urine in all patients on our CAPD programme, and calculated the daily CrEx ratio. Non-compliance was defined as a progressive and greater than 7.5% decrease of the CrEx ratio associated with a more than 7.5% decrease of serum creatinine during the test.

Among 19 patients only one (5%) fulfilled both criteria for non-compliance and the subsequent interview revealed that he was truly non-compliant. The other patient admitting non-compliance had a significant decrease of CrEx ratio but showed only a slight decrease of serum creatinine.

Our preliminary results suggest that this 3-day collection test, unlike previous procedures, identifies non-compliance with a good specificity. However, it may not be sensitive enough to detect a low level of non-compliance and has the disadvantage of being quite cumbersome. It may require further refinements to be clinically useful.