Which of the following is a sign of worsening renal function in cardiorenal syndrome?

In cardiorenal syndrome, an important sign of worsening renal function is a change in serum creatinine greater than 0.3 mg/dL. Serum creatinine is a key biomarker used to assess kidney function; an increase indicates that the kidneys are not filtering waste effectively, which can occur as a result of heart failure.

When the heart is not pumping efficiently, it affects blood flow to the kidneys, leading to renal hypoperfusion. This can result in elevated serum creatinine levels, signaling that renal function is deteriorating. A change of more than 0.3 mg/dL is particularly significant in clinical practice, as it indicates a notable shift in kidney performance that may require further evaluation and intervention.

Other options, such as a decrease in serum creatinine or an increase in urine output, typically suggest improving kidney function. Stable renal function would not indicate deterioration, making these options less relevant to the context of worsening renal function in the setting of cardiorenal syndrome.