Assessment of renal function in recently admitted critically ill patients with normal serum creatinine.

Background: Detection of renal dysfunction is important in critically ill patients, and in daily practice, serum creatinine is used most often. Other tools allowing the evaluation of renal function are the Cockcroft-Gault and MDRD (Modification of Diet in Renal Disease) equations. These parameters may, however, not be optimal for critically ill patients. The present study evaluated the value of a single serum creatinine measurement, within normal limits, and three commonly used prediction equations for assessment of glomerular function (Cockcroft-Gault, MDRD and the simplified MDRD formula), compared with creatinine clearance (Ccr) measured on a 1 h urine collection in an intensive care unit (ICU) population.

Methods: This was a prospective observational study. A total of 28 adult patients with a serum creatinine <1.5 mg/dl, within the first week of ICU admission, were included in the study. Renal function was assessed with serum creatinine, timed 1 h urinary Ccr, and the Cockcroft-Gault, MDRD and simplified MDRD equations.

Results: Serum creatinine was in the normal range in all patients. Despite this, measured urinary Ccr was <80 ml/min/1.73 m2 in 13 patients (46.4%), and <60 ml/min/1.73 m2 in seven patients (25%). Urinary creatinine levels were low, especially in patients with low Ccr, suggesting a depressed production of creatinine caused by pronounced muscle loss. Regression analysis and Bland-Altman plots revealed that neither the Cockcroft-Gault formula nor the MDRD equations were specific enough for assessment of renal function.

Conclusions: In recently admitted critically ill patients with normal serum creatinine, serum creatinine had a low sensitivity for detection of renal dysfunction. Furthermore, the Cockcroft-Gault and MDRD equations were not adequate in assessing renal function.