title: Comparison of measured and predicted creatinine excretion is an unreliable index of compliance in PD patients.
abstract: OBJECTIVE
  To evaluate the use of the ratio of measured to predicted creatinine excretion as an index of compliance in peritoneal dialysis (PD) patients.
  
  
  METHODS
  A prospective analysis.
  
  
  METHODS
  Academic teaching hospital dialysis unit.
  
  
  METHODS
  Forty-three patients on PD.
  
  
  METHODS
  Creatinine excretion in daily dialysate and urine collections was measured on one occasion in 10 patients and on two occasions in 33 patients, and, after adding an estimate for extrarenal creatinine degradation, was divided by predicted creatinine excretion to give a creatinine excretion ratio, which has been proposed as an index of compliance with exchanges in PD patients. Values above 1.24 have been suggested to indicate noncompliance. Lean body mass was also estimated from creatinine excretion.
  
  
  RESULTS
  The mean creatinine excretion ratio was 1.12, and 30% of patients had a value above 1.3. Only one patient admitted noncompliance. Studies on four consecutive days of guaranteed compliance in 7 patients with high ratios showed that creatinine excretion remained constant, suggesting that the patients were high creatinine producers rather than noncompliant. Creatinine excretion was stable when measured at intervals of days, but over months it tended to change markedly in many patients. Lean body mass estimations using creatinine excretion were low in most patients.
  
  
  CONCLUSIONS
  Comparison of measured and predicted creatinine excretion is not a reliable indicator of noncompliance because many compliant patients consistently excrete more creatinine than predicted. The standard formulas were not validated in dialysis patients and underestimate creatinine excretion significantly in many PD patients. Existing estimates in the literature of noncompliance, using this methodology, may not be accurate. Better methods of detecting this problem are required.
authors.affiliation: Victoria Hospital, and the University of Western Ontario, London, Canada.
authors.forename: P G
authors.initials: PG
authors.lastname: Blake
authors.forename: E
authors.initials: E
authors.lastname: Spanner
authors.forename: S
authors.initials: S
authors.lastname: McMurray
authors.forename: R M
authors.initials: RM
authors.lastname: Lindsay
authors.forename: E
authors.initials: E
authors.lastname: Ferguson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D001835:Body Weight; D003404:Creatinine / Q000032:analysis* / Q000652:urine; D015314:Dialysis Solutions / Q000737:chemistry; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010349:Patient Compliance; D010530:Peritoneal Dialysis; D010531:Peritoneal Dialysis, Continuous Ambulatory; D011446:Prospective Studies
chemical_list: D015314:Dialysis Solutions; D003404:Creatinine