ESTIMATING CREATININE CLEARANCE IN ELDERLY PATIENTS WITH LOW SERUM CREATININE CONCENTRATIONS

The accuracy of creatinine clearance (CL(cr)) estimates generated for elderly patients with a low serum creatinine (SCr) concentration when the SCr concentration was rounded to 1.0 mg/dL was evaluated, and dail y aminoglycoside dosages calculated with CL(cr) estimates based on the actual and the rounded SCr concentrations were compared with the actu al dosage required as determined by aminoglycoside concentration measu rements. Twenty-four-hour urine collections were obtained from elderly hospitalized patients with stable renal function, and CL(cr) was meas ured. SCr concentrations were measured at baseline, during urine colle ction, and after urine collection. CL(cr) was calculated twice with ea ch of seven methods, once by using the actual SCr concentration and on ce by rounding the SCr concentration to 1.0 mg/dL. Rounding the SCr co ncentration to 1.0 mg/dL resulted in significant underestimation of CL (cr) by all seven methods. The Cockcroft-Gault equation used with idea l body weight and the rounded SCr concentration resulted in the larges t bias. For six of the seven methods, bias was greater and precision l ess when SCr concentrations of <0.7 mg/dL were rounded than when SCr c oncentrations of greater than or equal to 0.7 mg/dL were rounded. The Bjornsson method used with the actual SCr concentration appeared to of fer the best combination of low bias and high precision. The required aminoglycoside dosage was significantly underestimated when the rounde d SCr concentration was used. In elderly patients with low SCr concent rations, rounding the SCr concentration to 1.0 mg/dL led to underestim ates of both CL(cr) and the correct aminoglycoside dosage.