An audit of 24-hour creatinine clearance measurements at Tygerberg Hospital and comparison with prediction equations.

BACKGROUND Internationally, clinical guidelines recommend the use of creatinine-based equations to estimate glomerular filtration rate (GFR) for assessment and follow-up of kidney disease. The routine use of 24-hour creatinine clearances (CrCl) is no longer advocated. OBJECTIVES To examine the indications for requesting CrCl at Tygerberg Hospital, identify problems associated with the procedure, and evaluate the utility of the Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) equations with different levels of renal dysfunction in the ethnic groups of the Western Cape. METHODS A clinical audit of CrCl was performed. The estimated GFR as predicted by the modified CG and MDRD formulae was compared with CrCl in 252 patients, representing three local ethnic groups. MDRD formulae with and without the correction factor for black ethnic group (MDRD-B) were evaluated. RESULTS Problems with urine collection or data supplied were identified in one-third of CrCl requests, leading to unreliable results. The CG correlated best with CrCl in the group as a whole. The average absolute and percentage differences from CrCl in the different ethnic groups were as follows: coloured (mixed ethnicity) (N = 186) - CG 13.4 ml/min/1.73 m(2) (18%), MDRD 16.8 ml/min/1.73 m(2) (23%) and MDRD-B 27.9 ml/ min/1.73 m(2) (38%); black (N = 21) - CG 14.8 ml/min/1.73 m(2) (19%), MDRD 12.9 ml/min/1.73 m(2) (17%) and MDRD-B 25.1 ml/min/1.73 m(2) (33%); white (N = 45) CG 13.5 ml/min/1.73 m2 (19%), MDRD 15.3 ml/min/1.73 m(2) (21%) and MDRD-B 24.8 ml/min/1.73 m(2) (35%). Throughout the renal function levels (chronic kidney disease stages 1 - 5) CG correlated better with CrCl than MDRD. CONCLUSIONS Possible reasons for poor correlations include a high prevalence of obesity, underweight and normal GFR in the study population. There is a need for further research, using a gold standard, into the accuracy of these prediction equations in our unique patient populations before firm recommendations can be made regarding their use. Until then CrCl will continue to be widely used. Greater efforts at patient and health care worker education are required to ensure proper collections.