Nursing care
24-hour urine collection: discard the first void, keep the last, and handle missed voids
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
Start a 24-hour urine collection by having the patient void and discarding that urine, then record the start time. Collect every void for the next 24 hours, including a final void at the end time. Keep the container cold, follow preservative instructions, and restart according to lab policy if any urine is lost or discarded.
Why the timing rule matters
A 24-hour collection measures how much of a substance, such as creatinine, protein or certain hormones, is excreted over a full day. The calculation assumes that exactly 24 hours of urine production is in the container. Urine already in the bladder at the start was made before the collection period, so it is discarded.
At the end, the patient voids into the container at the stated finish time, because that urine was produced during the collection window. Adding the first void or omitting the last one shifts the window and distorts results. Some tests, such as creatinine clearance, also need a blood sample drawn during the collection, so coordinate timing with the laboratory.
Step by step on the unit
Confirm the test ordered and any diet or medication instructions from the laboratory. Label the container with patient details and the start date and time. Ask the patient to void, discard that urine, and write the start time on the container and in the record. Place a sign in the bathroom and inform the team so no void is thrown away by mistake.
Collect each subsequent void in a clean collection hat or urinal and transfer all of it to the large container. Ask the patient not to mix in stool or toilet tissue. For a catheterised patient, keep the drainage bag cold or empty it into the container regularly. At the finish time, ask the patient to void and add that urine, then record the end time.
Storage and preservatives
Keep the container refrigerated or in a basin of ice throughout the collection unless the laboratory instructs otherwise, because warmth allows bacterial growth and breakdown of some substances. Store it upright with the lid closed to prevent leaks, and avoid freezing. Send the container promptly at the end with a completed request.
Some tests require a preservative, which may be an acid, already placed in the container. Teach the patient not to pour it out, not to urinate directly into a container holding a caustic preservative, and to avoid skin contact. Check that the preservative matches the test, because the wrong container can make the sample unusable.
Missed, spilled or discarded voids
If a void is missed, spilled or flushed, the total no longer represents 24 hours and the result may be falsely low. Do not try to estimate the lost amount. Notify the laboratory or provider and follow local policy, which commonly means discarding the collection and restarting with a new container and a new start time.
Prevention is easier than repetition. Remind assistive staff and visitors, keep the collection hat in place, and teach outpatients reminder strategies. Document the start and end times, the total volume if your unit records it, any interruption, and when the specimen was sent. Report a collection that seems inappropriately small for the patient's fluid intake.
Apply it to a hypothetical exam-style item
In an invented scenario, a collection started at 0700. At 1500 an assistant reports that a void was accidentally discarded. The options are to continue and note the missed void, add an estimated volume, end the collection early, or stop, inform the laboratory and restart with a new start time according to policy. Restarting is correct.
Continuing produces an inaccurate total, and estimating volume introduces guesswork into a quantitative test. For a second variation, a learner asks whether the 0700 void should be saved: it should be discarded, while the void at 0700 the next day is kept. Teach-back helps patients doing home collections avoid both errors.
Sources and further reading
MedlinePlus: Urine 24-hour volume. Urinating into the toilet on waking on day one, collecting all subsequent urine, voiding into the container on day two, refrigeration and labelling.
NIDDK Central Repository: HALT PKD instructions for 24-hour urine collection. Discarding the first void while recording the time, including the final void, keeping urine separate from stool, refrigerated upright storage and lost specimen making a collection unacceptable.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our dosage calculation and lab values practice questions are the closest set to what this page covers.
Common questions
Is the first void saved in a 24-hour urine collection?
No. The patient voids at the start time and that urine is discarded, because it was made before the collection began. Every later void is saved, including the final one.
What should the nurse do if a void is discarded?
Report it and follow lab policy, which usually means discarding the collection and restarting with a new container and start time. Do not estimate the missing amount.
Does the urine need to be kept cold?
Usually yes. Keep it refrigerated or on ice during the collection unless the laboratory says otherwise, and follow any preservative instructions for the specific test.
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