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The kidneys are particularly vulnerable to certain types of injury for a number of reasons. First, they are dependent upon the heart and vasculature to deliver sufficient blood supply to drive glomerular filtration (GFR). Secondly, they are major excretory organs, exposed to numerous endogenous and exogenous substances that are eliminated from the body via the urine. Acute kidney injury (AKI) can occur due to a variety of localized or systemic disease states, toxicity from chemicals or medicinal agents, or as the result of poor perfusion or outlet obstruction. It may be difficult to evaluate and diagnose because more than one type of damage may occur simultaneously, or one type of damage may occur secondary to another type. Although the incidence of AKI is greatest in hospitalized patients, it may also occur in patients residing in the community. Acute kidney injury is also very interesting because, in many cases, if the cause is identified and stopped promptly there may not be any permanent damage to the kidney. More severe, prolonged, or untreated injury can ultimately lead to permanent damage and even complete loss of kidney function.

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The kidneys have an incredible reserve capacity. Although a single insult may be sufficient to cause AKI, in many cases it is a combination of two or more factors that ultimately overwhelm the kidneys' ability to maintain GFR. Factors such as the presence of underlying chronic kidney disease (CKD), as well as the severity, extent, multiplicity, and duration of the injuries/insults, will determine how much damage (if any) will result and possibly persist.

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Definition

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There is no exact definition for AKI. Generally, the diagnosis is considered when there has been a relatively sudden and significant decrease in kidney function. Serum creatinine (SCr) is a metabolic byproduct of muscle metabolism and unless there is a significant change in muscle mass the serum concentration of an individual should remain relatively constant. An increase in the SCr concentration is generally the result of accumulation due to a decrease in the GFR. As chronic kidney disease may result in a higher baseline SCr value, the diagnosis of AKI is based on the change in SCr from baseline as well in changes in urine production.

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Incidence

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The incidence of AKI in the United States appears to be increasing. A community-based study showed an increase in cases of AKI from 323 cases per 100,000 in 1988 to 522 cases per 100,000 in 2002.1 There has also been an increase in hospital-acquired AKI2 with recent incidence estimated to be >7% in patients undergoing surgical procedures.3 The incidence of AKI in the community setting has been difficult to evaluate.1 The variation in the definition of AKI and the use of SCr concentration to define AKI as the primary marker of kidney function are particularly problematic in an aging population.4,5 As the incidence of AKI is ...

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