Last updated: 11/24/2009

Normal values for many tests are determined by the patient's age and gender. Reference values can also vary by laboratory, but are generally within the following ranges:

Urine tests

• Creatinine clearance. For a 24-hour...
  
  urine collection, normal results are 90 mL/min–139 mL/min for adult males younger than 40, and 80–125 mL/min for adult females younger than 40. For people over 40, values decrease by 6.5 mL/min for each decade of life.
• Urine osmolality. With restricted fluid intake (concentration testing), osmolality should be greater than 800 mOsm/kg of water. With increased fluid intake (dilution testing), osmolality should be less than 100 mOSm/kg in at least one of the specimens collected. A 24-hour urine osmolality should average 300–900 mOsm/kg. A random urine osmolality should average 500–800 mOsm/kg.
• Urine protein. A 24-hour urine collection should contain no more than 150 mg of protein.
• Urine sodium. A 24-hour urine sodium should be within 75–200 mmol/day.

Blood tests

• Blood urea nitrogen (BUN) should average 8–20 mg/dL.
• Creatinine should be 0.8–1.2 mg/dL for males, and 0.6–0.9 mg/dL for females.
• Uric acid levels for males should be 3.5–7.2 mg/dL and for females 2.6–6.0 mg/dL.

Low clearance values for creatinine indicate a diminished ability of the kidneys to filter waste products from the blood and excrete them in the urine. As clearance levels decrease, blood levels of creatinine, urea, and uric acid increase. Because it can be affected by other factors, an elevated BUN, alone, is suggestive, but not diagnostic for kidney dysfunction. An abnormally elevated plasma creatinine is a more specific indicator of kidney disease than is BUN.

Low clearance values for creatinine and urea indicate a diminished ability of the kidneys to filter these waste products from the blood and to excrete them in the urine. As clearance levels decrease, blood levels of creatinine and urea nitrogen increase. Since it can be affected by other factors, an elevated BUN alone is certainly suggestive for kidney dysfunction. However, it is not diagnostic. An abnormally elevated blood creatinine, a more specific and sensitive indicator of kidney disease than the BUN, is diagnostic of impaired kidney function.

The inability of the kidneys to concentrate the urine in response to restricted fluid intake, or to dilute the urine in response to increased fluid intake during osmolality testing, may indicate decreased kidney function. Because the kidneys normally excrete almost no protein in the urine, its persistent presence, in amounts that exceed the normal 24-hour urine value, usually indicates some type of kidney disease.

Patient education

Some kidney problems are the result of another disease process, such as diabetes or hypertension. Doctors should take the time to inform patients about how their disease or its treatment will affect kidney function, as well as the different measures patients can take to help prevent these changes.