Significant differences when using creatinine, modification of diet in renal disease, or cystatin C for estimating glomerular filtration rate in ICU patients

Abstract

Background. Renal dysfunction is associated with increased morbidity and mortality in intensive care patients. In most cases the glomerular filtration rate (GFR) is estimated based on serum creatinine and the Modification of Diet in Renal Disease (MDRD) formula, but cystatin C-estimated GFR is being used increasingly. The aim of this study was to compare creatinine and MDRD and cystatin C-estimated GFR in intensive care patients.

Methods. Retrospective observational study was performed, on patients treated within the general intensive care unit (ICU) during 2004–2006, in a Swedish university hospital.

Results. GFR markers are frequently ordered in the ICU; 92% of the patient test results had cystatin C-estimated GFR (eGFR_cystatinC) ≤ 80 mL/min/1.73 m², 75% had eGFR ≤ 50 mL/min/1.73 m², and 30% had eGFR ≤ 20 mL/min/1.73 m². In contrast, only 46% of the patients had reduced renal function assessed by plasma creatinine alone, and only 47% had eGFR_MDRD ≤ 80 mL/min/1.73 m². The mean difference between eGFR_MDRD and eGFR_cystatinC was 39 mL/min/1.73 m² for eGFR_cystatinC values ≤ 60 mL/min/1.73 m².

Conclusions. GFR is commonly assessed in the ICU. Cystatin C-estimated GFR yields markedly lower GFR results than plasma creatinine and eGFR_MDRD. Many pharmaceuticals are eliminated by the kidney, and their dosage is adjusted for kidney function. Thus, the differences in GFR estimates by the methods used indicate that the GFR method used in the intensive care unit may influence the treatment.