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Urine is a watery fluid produced by the kidneys as a waste product of metabolism. It consists mainly of water and dissolved solutes, including urea, electrolytes, creatinine, uric acid, and minor organic molecules. The composition can vary with hydration, diet, and health.

In the kidneys, blood is filtered in the glomeruli to form a filtrate. Through tubular reabsorption and secretion, the filtrate is modified to become urine, which is excreted through the ureters into the bladder and expelled via the urethra. Typical daily volume ranges from about 1 to 2 liters in healthy adults. The concentration of urine is regulated by antidiuretic hormone, which adjusts water reabsorption in the collecting ducts.

Urine analysis (urinalysis) is a common diagnostic tool. Parameters include color, clarity, odor, specific gravity, pH, and chemical tests for protein, glucose, ketones, bilirubin, and blood. Microscopic examination can reveal cells, crystals, cast formations, or bacteria. Abnormal findings may indicate dehydration, kidney disease, urinary tract infection, diabetes, liver disorders, or metabolic issues.

Urine is generally sterile in the bladder, though contamination can occur. Collection, storage, and handling are important for accurate testing. Some compounds are used as biomarkers, such as creatinine for renal function and urea as nitrogenous waste.