The 24-hour urine test is an analysis of urine that is collected over 24 hours. It is ordered to evaluate kidney function and helps to identify and monitor kidney diseases.

This test is mainly indicated to measure kidney function or to evaluate levels of proteins or other substances in the urine, such as sodium, calcium, oxalate or uric acid. It can also help to detect UTIs.

To carry out this test, you will be given a specific container to collect all of your urine over a period of 24 hours. It is then taken to the laboratory for analysis.

Why it's ordered

The 24-hour urine test is used to evaluate kidney function. It detects abnormalities in the kidneys by checking the levels of specific substances, like:

Creatinine clearance, which assesses the kidneys' filtration rate
Proteins, including albumin
Sodium
Calcium
Uric acid
Citrate
Oxalate
Potassium

Other substances such as ammonia, urea, magnesium and phosphate can also be checked in the urine.

The 24 hour urine test can help the doctor identify problems such as kidney failure, kidney tubule diseases, or the underlying cause of kidney stones. It can also be useful for detecting nephritis, which is a set of diseases that cause inflammation of the kidney glomeruli.

During pregnancy, this test is usually used to determine the presence of proteins in the pregnant woman's urine for the diagnosis of pre-eclampsia. This is a complication that arises during pregnancy that is associated with hypertension, fluid retention and loss of protein through the urine.

How to perform

To perform a 24 hour urine test, you do not need to do any type of preparation. Follow the following steps:

Obtain a collection container from your lab.
Start the next day. When you wake up first thing in the morning, urinate in the toilet, and discard the first urine of the day.
Write down the exact time you urinated in the toilet;
Collect all the rest of urine from the day and night into the container;

The last urine to be collected in the container must be at the same time as the previous day's urine in the toilet, with a tolerance of 10 minutes.

For example, if the person urinated at 8 am of the day, the urine collection must end at exactly 8 am the next day or at the earliest at 7:50 am and at the latest at 8:10 am.

Care during urine collection

During a 24-hour urine collection, certain precautions should be taken, such as:

If you are going to have a bowel movement, be sure not to urinate in the toilet, as all the urine should be collected in the container;
If you are going to take a shower, do not urinate in the shower
If you leave the house, you have to take the container with you or you won't be able to urinate until you return home
You cannot take a 24-hour urine test while menstruating.

Between urine collections, the container should be in a cool place, preferably refrigerated. When collection is complete, the container must be taken to the laboratory as quickly as possible.

Normal levels

The normal reference values for a 24-hour urine test are as follows:

Creatinine clearance: between 80 and 120 ml/min, which may be reduced in kidney failure.
Albumin: less than 30 mg per 24 hours
Total proteins: less than 150 mg per 24 hours
Calcium: without diet up to 280 mg per 24h and with diet 60 to 180 mg per 24h.

These values can vary depending on the person's age, gender, health condition and the laboratory's reference values. The results should be evaluated by the ordering doctor, who will determine next steps.

Because the 24 hour urine test is difficult to collect, frequent errors that can occur. Therefore, it is being less used in medical practice and is being replaced by other tests, that involve mathematical formulas used on a simple urine test.