Urine consists of waste material, excess water and toxic substances which need to be thrown out of the body regularly. Creatinine is the waste product which is generated during muscle metabolism. Proteins, as you know, are the building blocks of the body. Intake of sufficient protein promotes proper functioning of all body systems, growth and muscle building. Protein is not a waste product and hence it is retained in the blood by the kidneys during the process of blood-filtration. The structure of the glomeruli in kidneys is so perfect that relatively larger molecules of protein cannot pass through them. Therefore, a negligible amount of protein is found in a normal urine sample.
How to Prepare for the Test
You might be required to stop your routine medications before collecting the urine for testing. Certain drugs, for example, antibiotics, gentamicin, non-steroidal anti-inflammatory drugs, etc. can interfere with the test results and hence the doctor might instruct you to stop taking these drugs. You need to collect your urine in a special bag that would be provided to you. There is no discomfort or pain in this procedure.
How to Collect a 24 Hour Urine Sample
On the first day, you are supposed to urinate into the toilet after waking up in the morning. Then, you are supposed to collect all the urine in the special container, provided by the lab/doctor, and continue with the collection each time you urinate, during the next 24 hours. The next day, after waking up in the morning, you should urinate into the container again. The urine collected in this way is referred to as the '24 hour urine sample'. Do not forget to close the container correctly, every time you collect the urine. And you will be required to place it in a refrigerator or store in a cool place till you return it to the lab.
The process of collection is relatively easier for adults but not so in case of infants. A doctor or lab technician will be able to guide you regarding how to collect a 24 hour urine sample for infants. In case of baby boys, you can place the penis into the bag and lock the bag by attaching adhesive to the skin. In case of baby girls, place the bag over the labia and cover the area with a diaper. Parents need to check the bag frequently, so as to ensure that the urine is properly collected in the bag. Do not forget to wash the area around the urethra before placing the bag.
Normal Values for 24 Hour Urine Test
During routine analysis of urine, usually, a dipstick urine protein test is performed. If a higher amount of protein is detected in dipstic or random urine test, then 24 hour urine test is conducted. Urine collected randomly at any time during the day is referred to as 'random urine sample'. Mainly, the protein 'albumin' is found in greater amounts in the urine sample, in case of kidney dysfunction; because albumin is present in large quantities, in our blood. This test helps measure not only albumin but also other proteins. The following table shows the normal values of protein and creatinine in urine:
|Protein in a 24-hour sample of urine||Less than 150 mg|
|Creatinine in a 24 hour sample of urine||between 500 - 2000 mg/day|
|24 hour creatinine clearance in females||0.6 - 1.6 grams|
|24 hour creatinine clearance in males||0.8 - 1.8 grams|
|Rate of creatinine clearance for men||90 to 140 milliliters per minute or 1.78 to 2.32 milliliters per second|
|Rate of creatinine clearance for women||87 to 107 milliliters per minute or 1.45 to 1.78 milliliters per second|
|Urine protein to creatinine ratio in children under the age of two years||less than 0.5 grams of protein per gram of creatinine|
|Urine protein to creatinine ratio in adults and children over 2 years||less than 0.2 grams of protein per gram of creatinine|
Abnormal Values for 24 Hour Urine Test
|Protein in a 24-hour sample of urine||More than 150 mg||Proteinuria|
|Albumin creatinine ratio||around 35 - 300 mg per gram of creatinine||Albuminuria|
|Albumin creatinine ratio||greater than 30 mg per gram of creatinine||Microalbuminuria|
|Urine protein to creatinine ratio||greater than 3.5 grams of protein per gram of creatinine||Kidney Dysfunction|
Elevated protein levels in urine or low creatinine levels in urine suggest kidney dysfunction. Several disorders like urinary tract infection, bladder tumor, kidney infection, congestive heart failure, infection of the glomerulus of the nephron, high blood pressure, uncontrolled diabetes, lupus erythematosus, dehydration, etc. can affect kidney function. Since men have more muscle mass than women, higher creatinine clearance is natural for men. Creatinine clearance decreases with aging. It decreases by about 6.5 milliliters per minute for every 10 years, after reaching 30 years of age.
I hope the above information has helped you understand how a 24 hour urine test helps assess kidney function. Normal protein and creatinine clearance is a sign of healthy kidneys. Those who are being treated for kidney dysfunction, need to monitor the amount of protein and creatinine present in urine regularly, to check the effectiveness of the treatment. High protein in urine is asymptomatic in the earlier stages. Routine blood and urine tests are thus helpful for prompt diagnosis.