Prediction of Glomerular Filtration Rate Using Aminoglycoside Clearance in Critically Ill Medical Patients

Abstract

OBJECTIVE:

The aim of this preliminary investigation was to evaluate the use of aminoglycoside serum concentrations as a surrogate measure of the glomerular filtration rate (GFR) in comparison with other measured and empiric methods against inulin, the criterion standard measure of GFR.

DESIGN:

A consecutive sample of all eligible patients.

SETTING:

An eight-bed medical intensive care unit in a university-affiliated tertiary-care teaching hospital.

PATIENTS:

Ten critically ill medical patients receiving gentamicin or tobramycin for presumed or documented gram-negative bacillary infection were enrolled in the study. The patients were mechanically ventilated and had underlying organ system dysfunction. All ten patients completed the study.

INTERVENTION:

Patients underwent renal functional assessment by measured inulin (Cl_in) and 24-hour urinary creatinine clearance (Cl_cr). Aminoglycoside serum concentrations were used to estimate GFR and were compared with the two measured methods and a creatinine clearance calculated with the Cockcroft-Gault method (Cl_CG). All evaluations were performed the same day.

RESULTS:

Cl_in averaged 51.6 ± 35.0 mL/min and serum creatinine ranged from 0.3 to 5.4 mg/dL (26.5 to 477.3 μmol/L). Steady-state peak and trough aminoglycoside concentrations were 6.1 ± 1.4 and 1.3 ± 0.9 μg/mL, respectively. There were no statistically significant differences between the various methods, although the aminoglycoside-calculated GFR (Cl_amg) 95 percent confidence intervals were smaller man Cl_cr and Cl_CG compared with Cl_in. Mean absolute errors were smaller with Cl_amg than with Cl_cr and Cl_CG. Regression results indicated that only Cl_ang and Cl_CG demonstrated agreement with Cl_in (lines not different from y=x). However, the Cl_amg showed closer agreement, with a mean square error almost half that of Cl_CG (9.6 vs. 18.1).

CONCLUSIONS:

Cl_amg can be used routinely as an estimate of GFR in critically ill patients, with less error man empiric methods.