What is Acute Kidney Injury?
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Updated May 12, 2014.
Acute Renal Failure (ARF), or more accurately, Acute Kidney Injury (AKI) is a term used to describe a sudden, abrupt decline in kidney function. But as you might imagine, defining "sudden and abrupt", and even the degree of "decline", specifically is hard. Just like Chronic Kidney Disease (CKD), the term AKI is a non-specific, catch-all diagnosis that defines the rapidity of development of kidney disease, rather than its cause or severity.
For instance, Non Steroidal Anti Inflammatory Drugs (NSAIDs) like ibuprofen can cause CKD. But they can also cause AKI! And both these entities can be present in the same patient at the same time. Hence, the definition of acute kidney injury has often been very arbitrary.
Defining acute kidney injury consistently is important not just for academic or research purposes, but also for patient care since we are well aware that acute kidney injury is associated with poor outcomes in those affected. Higher degree of acute kidney injury is associated with a higher risk of death (discussed later).
Nephrologists have been aware of this problem for a while. Hence, in 2004, a bunch of smart kidney docs decided to sit down and put together a definition/classification system for acute kidney injury. They came up with a cool sounding name called the RIFLE Criteria to define these sudden abrupt changes. Things continue to evolve further over the last decade. Finally, the Kidney Disease Improving Global Outcomes (KDIGO) organization fine tuned these criteria.
So, as per this latest evidence-based definition of acute kidney injury, you could potentially define acute kidney injury in any one of the following ways:
Although the above definition took away some of the arbitrariness associated with defining abrupt declines in kidney function, the classification system still has some drawbacks. One of the problems is that we are not sure if labeling someone with acute kidney injury solely based on a reduction in the urine output is clinically important or not. Another problem is not really with the classification per se, but more specifically with the use of creatinine as an indicator of kidney disease. We know that creatinine levels have to be interpreted in light of a person's muscle mass. Hence, while a creatinine of 1.8 may not be a big deal in Arnold Schwarzenegger, it definitely indicates profound kidney decline in a frail 95 year old woman.
We also know that creatinine levels can sometimes be affected by what you eat and what medications you are on (eg. bactrim). In these situations increases in creatinine might not necessarily be reflective of kidney disease. The hope is that in the future we might be able to identify better indicators in the blood or urine that diagnose the presence and severity of kidney injury.
Diagnosing and stratifying acute kidney injury is important for multiple reasons. Severe AKI could require dialysis support. However, statistically speaking, in most cases this is not required and AKI should resolve with proper supportive care. Unlike insidious, slowly progressive chronic kidney disease where reversing the decline in GFR might be harder (or impossible), it is the norm to see kidney function resolve to baseline in patients who have AKI. This depends on a lot of factors though, including presence of preexisting CKD, cause of AKI, severity of AKI, etc.
AKI, even when it resolves completely, could sometimes still have long term consequences. Patients who develop AKI have a much higher risk of developing chronic kidney disease (CKD), and even End Stage Kidney Disease when long term dialysis is required. Perhaps most importantly, patients who do develop AKI have an increased risk of death as well. Understanding the causes of AKI and taking aggressive preventive measures could save patients from these consequences.
Updated May 12, 2014.
Acute Renal Failure (ARF), or more accurately, Acute Kidney Injury (AKI) is a term used to describe a sudden, abrupt decline in kidney function. But as you might imagine, defining "sudden and abrupt", and even the degree of "decline", specifically is hard. Just like Chronic Kidney Disease (CKD), the term AKI is a non-specific, catch-all diagnosis that defines the rapidity of development of kidney disease, rather than its cause or severity.
For instance, Non Steroidal Anti Inflammatory Drugs (NSAIDs) like ibuprofen can cause CKD. But they can also cause AKI! And both these entities can be present in the same patient at the same time. Hence, the definition of acute kidney injury has often been very arbitrary.
THE NEED FOR A UNIFORM DEFINITION
Defining acute kidney injury consistently is important not just for academic or research purposes, but also for patient care since we are well aware that acute kidney injury is associated with poor outcomes in those affected. Higher degree of acute kidney injury is associated with a higher risk of death (discussed later).
Nephrologists have been aware of this problem for a while. Hence, in 2004, a bunch of smart kidney docs decided to sit down and put together a definition/classification system for acute kidney injury. They came up with a cool sounding name called the RIFLE Criteria to define these sudden abrupt changes. Things continue to evolve further over the last decade. Finally, the Kidney Disease Improving Global Outcomes (KDIGO) organization fine tuned these criteria.
So, as per this latest evidence-based definition of acute kidney injury, you could potentially define acute kidney injury in any one of the following ways:
- Increase in serum creatinine by =0.3 mg/dL (=26.5 micromol/L) within 48 hours
- Increase in serum creatinine by =1.5 times baseline over prior seven days
- Urine volume <0.5 mL/kg/h for six hours
PROBLEMS WITH CURRENT DEFINITION
Although the above definition took away some of the arbitrariness associated with defining abrupt declines in kidney function, the classification system still has some drawbacks. One of the problems is that we are not sure if labeling someone with acute kidney injury solely based on a reduction in the urine output is clinically important or not. Another problem is not really with the classification per se, but more specifically with the use of creatinine as an indicator of kidney disease. We know that creatinine levels have to be interpreted in light of a person's muscle mass. Hence, while a creatinine of 1.8 may not be a big deal in Arnold Schwarzenegger, it definitely indicates profound kidney decline in a frail 95 year old woman.
We also know that creatinine levels can sometimes be affected by what you eat and what medications you are on (eg. bactrim). In these situations increases in creatinine might not necessarily be reflective of kidney disease. The hope is that in the future we might be able to identify better indicators in the blood or urine that diagnose the presence and severity of kidney injury.
WHAT IT MEANS FOR THE PATIENT
Diagnosing and stratifying acute kidney injury is important for multiple reasons. Severe AKI could require dialysis support. However, statistically speaking, in most cases this is not required and AKI should resolve with proper supportive care. Unlike insidious, slowly progressive chronic kidney disease where reversing the decline in GFR might be harder (or impossible), it is the norm to see kidney function resolve to baseline in patients who have AKI. This depends on a lot of factors though, including presence of preexisting CKD, cause of AKI, severity of AKI, etc.
AKI, even when it resolves completely, could sometimes still have long term consequences. Patients who develop AKI have a much higher risk of developing chronic kidney disease (CKD), and even End Stage Kidney Disease when long term dialysis is required. Perhaps most importantly, patients who do develop AKI have an increased risk of death as well. Understanding the causes of AKI and taking aggressive preventive measures could save patients from these consequences.
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