A comparison of three methods to estimate baseline creatinine for RIFLE classification

Area of Science:

• Nephrology
• Critical Care Medicine
• Clinical Chemistry

Background:

• Accurate diagnosis of acute kidney injury (AKI) using the RIFLE classification requires a pre-morbid baseline creatinine value.
• The Modification of Diet in Renal Disease (MDRD) equation is frequently used to estimate baseline creatinine but lacks validation.

Purpose of the Study:

• To validate the use of the MDRD equation for estimating baseline creatinine in intensive care unit (ICU) patients.
• To develop and assess a new equation for estimating baseline creatinine in ICU patients.

Main Methods:

• Analysis of four ICU patient cohorts from three centers.
• Derivation of a new baseline creatinine estimation equation using anthropometric variables.
• Comparison of the new equation, MDRD equation, and gender-fixed estimates against measured creatinine values.

Main Results:

• All tested methods (MDRD, new equation, gender-fixed) demonstrated similar median absolute errors (0.1-0.2 mg/dl).
• Accuracy for classifying AKI severity varied: 78-90% for normal range cohorts and 63-70% for unselected ICU patients.
• The MDRD equation may misclassify mild AKI (Risk stage) but is less likely to misclassify moderate to severe AKI (Injury and Failure stages).

Conclusions:

• Estimating baseline creatinine introduces bias and limits accuracy in AKI incidence assessment for critically ill patients.
• Whenever feasible, utilizing recorded creatinine values is the preferred method for establishing a patient's baseline.
• The MDRD equation can be used cautiously for estimating baseline creatinine when recorded values are unavailable, acknowledging potential misclassification of mild AKI.