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.