The present disclosure provides methods of treating diuretic resistance by administering an IL-6 antagonist to patients who require diuresis. The present disclosure also provides methods of treating heart failure, and in particular renal symptoms of heart failure, by administering an IL-6 antagonist to heart failure patients who have at least one copy of the TMPRSS6 rs855791 major allele. Optionally, the patient has elevated urine levels of IL-6, plasma levels of IL-6, or both urine and plasma levels of IL-6. Also provided are methods of detecting cardiorenal syndrome in a patient comprising measuring a level of IL-6 in the patient's urine or plasma.本發明提供藉由向需要多尿(diuresis)之患者投與IL-6拮抗劑來治療利尿劑抗性之方法。本發明亦提供藉由向具有TMPRSS6 rs855791主要對偶基因之至少一個複本之心臟衰竭患者投與IL-6拮抗劑來治療心臟衰竭及尤其是心臟衰竭之腎症狀之方法。視情況,該患者具有較高尿液IL-6水準、較高血漿IL-6水準,或較高尿液IL-6水準及較高血漿IL-6水準。本發明亦提供偵測患者之心腎症候群之方法,該方法包含量測該患者尿液或血漿中的IL-6水準。