The term cardiorenal syndrome (CRS) increasingly has been used without a 
consistent or well-accepted definition. To include the vast array of 
interrelated derangements, and to stress the bidirectional nature of 
heart-kidney interactions, we present a new classification of the CRS with 5 
subtypes that reflect the pathophysiology, the time-frame, and the nature of 
concomitant cardiac and renal dysfunction. CRS can be generally defined as a 
pathophysiologic disorder of the heart and kidneys whereby acute or chronic 
dysfunction of 1 organ may induce acute or chronic dysfunction of the other. 
Type 1 CRS reflects an abrupt worsening of cardiac function (e.g., acute 
cardiogenic shock or decompensated congestive heart failure) leading to acute 
kidney injury. Type 2 CRS comprises chronic abnormalities in cardiac function 
(e.g., chronic congestive heart failure) causing progressive chronic kidney 
disease. Type 3 CRS consists of an abrupt worsening of renal function (e.g., 
acute kidney ischemia or glomerulonephritis) causing acute cardiac dysfunction 
(e.g., heart failure, arrhythmia, ischemia). Type 4 CRS describes a state of 
chronic kidney disease (e.g., chronic glomerular disease) contributing to 
decreased cardiac function, cardiac hypertrophy, and/or increased risk of 
adverse cardiovascular events. Type 5 CRS reflects a systemic condition (e.g., 
sepsis) causing both cardiac and renal dysfunction. Biomarkers can contribute to 
an early diagnosis of CRS and to a timely therapeutic intervention. The use of 
this classification can help physicians characterize groups of patients, 
provides the rationale for specific management strategies, and allows the design 
of future clinical trials with more accurate selection and stratification of the 
population under investigation.