Compare and contrast the utility of the following in the assessment of acute kidney injury in a critically ill patient:
- Creatinine clearance
- Serum creatinine
- Urine output measurements
- Novel biomarkers
Answer and interpretation
- 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.
- 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
- 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
- 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
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.