Which substance's abnormal levels in urine can indicate kidney damage?

Albumin is a protein that is typically retained in the bloodstream, with only trace amounts found in urine. When there are abnormal levels of albumin in urine, a condition known as albuminuria occurs, which can be indicative of kidney damage or dysfunction. The kidneys normally filter waste and excess substances from the blood while preventing the loss of important proteins like albumin. Elevated albumin levels in urine suggest that the filtration barrier of the kidneys (the glomeruli) may be compromised, allowing proteins to leak into the urine—a common sign of conditions such as diabetic kidney disease or glomerulonephritis.

In contrast, while glucose, creatinine, and calcium can also be present in urine, their abnormal levels do not directly point to kidney damage in the same way. For example, glucose can appear in urine during diabetes but is not solely indicative of kidney dysfunction. Creatinine levels are often monitored to assess overall kidney function but do not specifically indicate kidney damage when present in urine. Elevated calcium can be linked to various metabolic conditions, but it isn't a specific marker for kidney damage like albumin is.