Urea is a low molecular weight substance that is freely filtered by glomeruli, and the majority is excreted into the urine, although variable amounts are reabsorbed along the nephron. Urine urea nitrogen is a measure of protein breakdown in the body. Urea is excreted by the kidneys, so excretion of urea can reflect kidney function. Approximately 50% of urinary solute excretion and 90 " 95% of total nitrogen excretion is composed of urea under normal conditions.
Normal range:
Twenty-four " hour urine: 2 " 20 g/day
Random urine:
Male: 2.8 " 9.8 g/g creatinine
Female: 3.1 " 11.6 g/g creatinine
Use
Determination of a persons protein balance and the amount of dietary protein needed by severely ill patients
Interpretation
Increased In
Too much protein intake and/or increased protein breakdown in the body
Hyperthyroidism
Decreased In
Malnutrition
Kidney damage and insufficiency from any cause
Normal growing children and infants
Pregnancy
Low-protein and high-carbohydrate diet
Liver disease
Limitations
Levels increase with age and protein content in the diet.
Administration of GH, testosterone, and insulin decrease the urine levels.