Equipment
Specimen container—disposable plastic containers
are preferred. The container should be large,
usually 4 L. The appropriate preservative
should be placed into the container prior to the
start of the collection. Preservatives are usually
added by the laboratory. If the analyte to be
assayed is light sensitive, a dark container is
necessary.
Procedure
1. Patient cooperation is imperative for a successful
timed urine collection so instruct the patient
carefully in the procedure and encourage his or
her cooperation.
2. Warn the patient if the urine preservative is
caustic.
3. Instruct the patient to discard a voiding and record
the time. For 24 h collections, it is usual to
discard the first morning voiding.
4. Have the patient collect every voiding for the
duration of the timed collection. The urine may
be collected in a wide-mouthed, chemically
clean container and then poured into the speci-
men container.
5. The specimen container should be kept refriger-
ated throughout the collection period.
6. The last urine collection should be a complete,
forced voiding at the exact end of the timed
period.
7. Seal the container tightly and submit the speci-
men immediately.
Sources of Variability
1. The specimen container should be chemically
clean.
2. The analyte of interest must be preserved during
the storage of the urine while the collection is in
progress. Light-sensitive analytes should be
shielded in dark bottles. Refrigeration is used to
retard bacterial growth as well as to stabilize
certain analytes. Acidification of the urine is
necessary to assure stability of a large number of
analytes.
3. Since the timed urine collection is used to calcu-
late an excretory rate, i.e. amount of analyte
excreted per unit time, it is imperative that the
collection be complete and properly timed.
Unfortunately, timed collections very frequently
are incomplete, usually because of the forgetful
discarding of a voiding during the collection.
Over-collection does happen but is much less
common. Variability in the completeness of the
collection is by far the most important variable
in timed collections. Consequently, care must
be taken to instruct the patient or nursing staff in
the importance of a complete collection.
Specimen Collection Procedures A-14
URINE: TIMED COLLECTION
