24-hour urine collection

The urine 24-hour volume test measures the amount of urine produced in a day, and the amounts of creatinine, protein, and other chemicals released into the urine during the same period are usually tested as well — sodium, potassium, urea nitrogen among them. A single sample shows concentrations at one moment; a 24-hour collection shows what the kidneys actually cleared over the whole day.

The collection follows a fixed ritual. On day 1, on getting up in the morning, the first urine goes into the toilet — it is not collected. From that moment every portion of urine for the next 24 hours goes into the special container. On day 2, the first morning urine is collected into the container, closing the 24-hour window.

Between trips to the bathroom the container stays capped and is kept in the refrigerator or a cool place for the whole collection period. At the end it is labeled with the name, the date, and the time of completion, and returned exactly as the laboratory instructed.

The normal range for 24-hour urine volume is 800 to 2,000 milliliters per day with a normal fluid intake of about 2 liters per day. Several things distort the result: dehydration, dye (contrast media) from a radiology scan within 3 days before the test, emotional stress, fluid from the vagina getting into the urine, strenuous exercise, and a urinary tract infection. Certain medicines also affect the results — the provider says which ones to pause, and no medicine is stopped without that conversation.

How the sample is collected

1. Pick up the special container and any instructions from the laboratory before the collection day.
2. On day 1, urinate into the toilet on waking — this portion is discarded, and the clock starts.
3. Collect every portion of urine into the container for the next 24 hours.
4. Keep the container capped and refrigerated or in a cool place between portions.
5. On day 2, collect the first morning urine into the container to finish the window.
6. Label the container with name, date, and completion time, and return it as instructed.

What can spoil the sample

• Collecting the first morning urine of day 1 — it belongs to the previous 24 hours and must be flushed.
• Missing a portion — one forgotten trip to the toilet makes the daily totals unusable.
• Leaving the container at room temperature instead of keeping it cool.
• Having a contrast-dye radiology scan within 3 days before the test without telling the provider.
• Strenuous exercise, dehydration, or unusual stress during the collection day — all three shift the numbers.

Tests that use this sample

Frequently asked questions

Sources