Which of the following molecules, if present in urine, indicates a problem with kidney function?

The presence of albumin in urine is an important indicator of kidney function. Under normal circumstances, the kidneys filter out waste products while retaining essential proteins, such as albumin, in the bloodstream. If albumin is detected in the urine, it suggests that the kidneys may be damaged or not functioning properly, as they are allowing this protein to leak into the urine. This condition is often referred to as proteinuria and can signify various kidney issues, such as glomerulonephritis or diabetic nephropathy.

In contrast, creatinine is a waste product resulting from muscle metabolism and is typically monitored to assess kidney function, but its presence alone in urine does not indicate a problem; instead, it's often evaluated in conjunction with blood levels. Sodium ions and water, while important components of urine composition, are normally filtered and reabsorbed by the kidneys and do not specifically signal kidney dysfunction when present in typical amounts.