M. Smythe et al., ESTIMATING CREATININE CLEARANCE IN ELDERLY PATIENTS WITH LOW SERUM CREATININE CONCENTRATIONS, American journal of hospital pharmacy, 51(2), 1994, pp. 198-204
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.