CICM SAQ 2010.1 Q2

Creatinine clearance

• Gives estimation of Glomerular Filtration Rate (GFR).
• Requires timed urine collection (usually 24 hours).
• Accuracy may be limited due to creatinine secretion, thus overestimating GFR, and incomplete urine collection.
• Assumes steady state in GFR, which may not be the case in acute renal failure.
• Determining exact GFR is rarely clinically necessary.

Serum creatinine

• Simple to measure and widely available.
• Specific for renal function.
• Indicator of GFR based upon constant production from muscle creatine and relatively constant renal excretion rate.
• Production may be increased by trauma, fever or immobilisation.
• Decreased in individuals with small stature, cachexia, reduced muscle mass (eg muscle disease, amputations)
• Decreased production may occur in liver disease because of decreased hepatic conversion of creatine to creatinine, decreased dietary protein intake, muscle wasting and increased renal tubular secretion of creatinine.
• May be influenced by volume of distribution changes in critically ill patients

Urea

• Simple to measure and widely available
• Not specific for renal function
• May be affected by liver disease, protein intake, catabolic state, volume status, upper gastrointestinal bleeding, and drug therapy – eg corticosteroids.

Urine output measurements

• Simple to measure and universally available.
• More sensitive to changes in renal function than biomarkers
• Non-specific – can have normal urine output despite severe acute renal failure

Novel biomarkers

• Include a plasma panel (NGAL and cystatin C) and urine panel (NGAL, IL-8 and KIM-1)
• Represent sequential biomarkers and so have potential for timing the initial insult and assessing the duration of AKI and for predicting overall prognosis
• May also distinguish between various types and pathogeneses of AKI
• Potential for high sensitivity and specificity
• So far only tested in small studies and limited clinical situations and need further validation