Searches were performed in PubMed, Scopus, and Web of Science using combinations of keywords such as “cardiorenal syndrome,” “biomarkers,” “heart failure,” “acute kidney injury,” “chronic kidney disease,” and specific marker names (e.g., NGAL, KIM-1, cystatin C, CA125, bio-ADM, FGF-23, etc.). The gene discussed is ADM; the disease is heart failure.