MEASURED VERSUS ESTIMATED CREATININE CLEARANCE IN PATIENTS WITH LOW SERUM CREATININE VALUES

OBJECTIVE: To examine, in patients with a serum creatinine (SCr) <85 m u Mol/L, whether the use of actual SCr versus the use of an SCr set at 85 mu mol/L and applied to the Cockcroft-Gault method for calculation of creatinine clearance (Cl-cr), resulted in a similar ability to exp lain variance in prediction of C1(cr). DESIGN: Included in the study w ere patients with stable renal function receiving total parenteral nut rition, who underwent a 24-hour urine collection and had an SCr <85 mu mol/L. Cl-cr was calculated (CalcCl(cr)) using the Cockcroft-Gault me thod, and actual SCr, and an SCr value set at 85 mu mol/L (AdjCalcCl(c r)). Calculated values were compared with 24-hour measured Cl-cr (Meas Cl(cr)). SETTING: Inpatient, acute-care hospital. PATIENTS: 33 patient s having 33 urine-collection periods. All patients were receiving tota l parenteral nutrition as their only form of nutritional supplement. P atients who had liver disease, trauma, or bums, or who were receiving certain pharmacologic agents, were excluded from the study. MAIN OUTCO ME MEASURES: MeasCl(cr) based on the 24-hour urine collection, CalcCl( cr) computed using the actual measured SCr, and SCr adjusted to 85 mu mol/L.RESULTS: A higher proportion of the variance of measured versus calculated Cl-cr was explained by the using the actual measured SCr va lue (r(2)=0.68) than SCr adjusted to 85 mu mol/L (r(2)=0.32). When ana lyzed by gender, adjusting the SCr to 85 mu mol/L was somewhat better at explaining the variance of measured versus calculated Cl-cr, but st ill explained less than 50 percent of the variance. However. the use o f the actual SCr explained more of the variance of measured versus cal culated Cl-cr than the use of the SCr value adjusted to 85 mu mol/L. C ONCLUSIONS: In patients with an SCr <85 mu mol/L, the actual measured SCr should be used when calculating Cl-cr (regardless of the patient's gender), by the Cockcroft-Gault method.