What's in a name, AKI?

Names of syndromes or diagnoses are part medicine and part marketing. The branding of a clinical paradigm with a name helps to identify the therapeutic plan. Without the clarity of a named diagnosis, however, this often does not happen. Acute kidney injury (AKI) has suffered from such a lack of identity. This has occurred because there are poor markers for identifying dysfunction and multiple different criteria are used for its definition. In the setting of liver failure, where the usual markers of kidney disease are less robust than normal, this leads to an even more disturbed ability to recognize kidney dysfunction. Additionally, as kidney dysfunction is only one of a multitude of problems that liver transplant recipients face, AKI without a distinct identity is lost in the list of therapeutic priorities. This all occurs even though it is well known that AKI negatively affects survival no matter what the patient population is. AKI, acute kidney injury; RIFLE, risk, injury, failure, loss, and end-stage kidney disease. Barri et al.1 set out to clarify the diagnosis of clinically significant AKI in liver transplant recipients from among the over 30 definitions used in the literature. The investigators selected 3 common definitions of AKI clearly representing different degrees of kidney dysfunction. The definitions were applied in a retrospective fashion to their program's large database. The primary outcome measures were patient and allograft survival. What new information does the study give us? Not much. We all know that kidney injury is common after liver transplantation. We all know that increasing amounts of kidney failure are bad. We all know that programs need to take steps to actively avoid kidney injury. However, what does the study show us that will affect our assessment of patients? A fair bit. This study focuses our attention on a definition of AKI that can reproducibly be associated with poor outcome while using a very simple and easily available measure, the degree of change in serum creatinine. This outcome, which includes longer intensive care unit and hospital stays, more sepsis, cytomegalovirus infection, cardiovascular events, and long-term kidney dysfunction (by iothalamate clearance), is seen in the short term, within 2 years. Criticisms of the article include exclusion of the Acute Dialysis Quality Initiative RIFLE (risk, injury, failure, loss, and end-stage kidney disease) criteria for the categorization of AKI established in 2004 (Table 1). RIFLE criteria, based on the worst of either the glomerular filtration or urine output criteria, have been shown to predict poor patient outcome in many situations, including liver transplantation.2-4 These criteria could have been applied to this article, and the other AKI definitions could have been compared with RIFLE; this would have further clarified the field.3, 4 That said, the study's most severe definition of AKI, a serum creatinine rise of >50% above baseline to above 2 mg/dL, compares roughly to failure in RIFLE. This is so because of the lower creatinine levels in people with liver disease and the likely underlying kidney dysfunction present at transplantation. Another study shortfall was the choice of the control group. The control group changed with each definition of AKI. Although this retained the most patients for assessment and analysis of the relativity of the definitions, it did not allow a comparison with those that clearly had no evidence of kidney injury. This methodology actually diluted the ability to demonstrate a change in outcome with different degrees of kidney dysfunction. Lastly, the importance of pretransplant kidney dysfunction on posttransplant risk for AKI was not analyzed, and cystatin-C, which has been shown to more accurately reflect kidney dysfunction in liver disease than serum creatinine, was not assessed.5 Where do we go from here? Should investigation into the occurrence and degree of kidney injury end with this study? Of course not. It is time, however, to turn our attention to identifying more precise and predictive markers of kidney injury while using the studies of Barri et al.1 and those that have used RIFLE criteria to prospectively identify, avoid, and/or treat, if possible, those risk factors that have been shown to lead to AKI.3, 4 It is also time to tighten up the criteria for initiation of dialysis and selection of the dialysis modality. It is time to give kidney dysfunction a clear identity and treatment strategy in the setting of liver transplantation.