Urine is commonly used for diagnostic testing and monitoring disease. Proper collection and preservation of urine specimens is important to avoid preanalytical errors. There are various urine collection methods depending on the test and patient, including random, first morning, and timed collections. Preservatives like boric acid and hydrochloric acid are often used to maintain specimen stability, though some tests require no preservative. Careful instruction of patients and labeling of specimens is necessary when collecting 24-hour urine samples.

1. Dr. K. Selvakumar
M.Sc., M.Phil., Ph.D., MBA (HM)
Consultant Biochemist
Billroth Hospitals & Kauvery Hospital
Urine PreservativesUrine Preservatives

2. Urine has a long history as a specimen for
analysis in clinical laboratories. After blood, urine
is the most commonly used specimen for
diagnostic testing, monitoring of disease status
and detection of drugs.

3. As with all clinical laboratory specimens,
preanalytical error in urine specimens is
often difficult to detect.

4. Types of Urine Collection Methods
Urine specimens may be collected in a variety of
ways according to the type of specimen required,
the collection site and patient type.
Randomly Collected Specimens are not
regarded as specimens of choice because of the
potential for dilution of the specimen when
collection occurs soon after the patient has
consumed fluids.

5. First Morning Specimen is the specimen of choice for
urinalysis and microscopic analysis, since the urine is
generally more concentrated.
Midstream Clean Catch Specimens are strongly
recommended for microbiological culture and antibiotic
susceptibility testing because of the reduced incidence of
cellular and microbial contamination.

6. Timed Collection Specimens - quantitative measurement
of certain analytes, including those subject to diurnal
variation.
Analytes commonly tested using timed collection include
creatinine, urea, potassium, sodium, uric acid,
cortisol, calcium, citrate, amino acids, catecholamines,
metanephrines, vanillylmandelic acid (VMA),
5-hydroxyindoleacetic acid, protein, oxalate,
copper,17-ketosteroids, and 17-hydroxysteroids.

7. Collection from Catheters (e.g. Foley catheter)using a
syringe, followed by transfer to a specimen tube or cup.
Alternatively, urine can be drawn directly from the
catheter to an evacuated tube using an appropriate
adaptor.

8. Supra-pubic Aspiration may be necessary when a non-
ambulatory patient cannot be catheterized or where there
are concerns about obtaining a sterile specimen by
conventional means.

9. Pediatric Specimens present
many challenges. For infants
and small children, a special
urine collection bag can be
adhered to the skin surrounding
the urethral area.

10. Types of containers

11. Collection and Transport Guidelines
All urine collection and/or transport containers should be clean and free
of particles or interfering substances.
The collection and/or transport container should have a secure lid and
be leak-proof. Leak-proof containers reduce specimen loss and risk of
healthcare worker exposure to the specimen while also protecting the
specimen from contaminants.
The use of containers that are made from break-resistant plastic is
strongly recommended.

12. • The container material should not leach interfering substances into the
specimen.
• Specimen containers must not be re-used.

13. Preservatives Used for Urine Collection
• The stability of some of the components excreted in the urine are
affected by the change in pH that occurs in the collected sample.
• Urine pH often becomes more alkaline upon collection due to the
presence and ongoing metabolism of bacteria and viable cells that are
excreted.
• Certain analytes are better suited for a pH that is closer to what is found
within the urinary system, while others require a more acidic pH to
minimize the deterioration of the desired measurands.
• The importance of such preservatives is stressed when collecting a 24-
hour urine sample to minimize the degradation associated with variable
handling and storage conditions.

14. Commonly used preservatives
Boric acid, hydrochloric acid, acetic acid, and oxalic
acid. Certain buffers and bicarbonate salts may also be
used for specific measurands.
Laboratories need to evaluate the effectiveness and
potential interference of preservatives.
Coordinators of urine sample collection need to
educate patients as to the safe and effective handling of the
preservatives when providing urine collection instructions.

15. Instructions to Patient:
The 24-hour collection container may contain chemicals (as a
preservative) that are hazardous. DO NOT urinate directly into the
container. Collect urine in a clean, dry vessel and carefully pour the urine
into the 24-hour collection container.
Follow your physician’s advice regarding any food, drink or drugs
before and during collection.
Empty your bladder completely upon awakening and discard this urine.
This is your start date and time. Write it on your paperwork and/or the
collection container.

16. • Collect all urine for the next 24 hours. The last urine collected should be
that voided upon awakening the second day, at the same time as the
start time.
(For Eg : Sample started at 8.00 AM. The patients should void the urine at 8.00 AM
and discard it, after that all the urine should be collected and poured / stored in a
container till the next 8.00 AM.)
• Recap the collection container carefully and completely.
• Return the collection container to the laboratory as soon as possible.
• Note: Some urine tests require that the 24-hour urine collection be
refrigerated during collection. Kindly instruct the patient accordingly.

17. Important Points for Lab Staff
It is necessary to measure the total volume excreted in a 24-hour period,
a strictly timed 24-hour specimen is required, because many soluble
substances exhibit diurnal variations.
Collect the specimen in one or more disposable, wide-mouthed, clean
plastic container(s) with a plastic lid large enough to hold about 3 L.
Amber-colored containers may be required for light-sensitive analytes.
 Copper |
Determine if the collection will require a preservative, ensuring the
collection container has the appropriate preservative, at the correct
concentration, along with a warning label indicating the preservative in use.

18.  Label the collection container including the patient identification (name and
hospital number), test(s) required, and preservative used.
 The start date and time plus the finish date and time should be recorded on
container sticker
 If a preservative is required, the patient must be advised to collect the urine in a
separate clean container and then carefully transfer the urine to the collection
container that will be transported to the laboratory. (Comment: Assume that all
preservatives are hazardous).
 Instruct the patient (or nurse) to collect all voided urine during the 24-hour
collection period and add it to the collection container.
 The collection should end exactly 24 hours. Record the ending date and time on
the collection container and on the laboratory requisition.
 Carefully seal the cap tightly so as to avoid leak

19. (*No)Preservatives
• Albumin (Microalbumin) (Only Thymol & Boric Acid)
• Calcium (Except Toluene & Sodium carbonate)
• Catecholamine Fractions (Except Toluene, Sodium carbonate, Diazolidinyl, Thymol)
• Chloride (Except Toluene, Sodium carbonate, 6N HCl, 6N HNO3)
• Free Cortisol (Only Acetic Acid, 6NHCl, 6N HNO3)
• Creatinine Clearance (Except Tolune)
• Metanephrines (Except Diazolidinyl, Thymol)
• Phosphorus (Except Toluene & Sodium carbonate)
• Potassium (Except Tolune)
• Sodium (Except Toluene & Sodium carbonate)
• Protein (Only Thymol & Boric Acid)
• Urea Clearance (Except Tolune)
• Uric Acid (Only Boric Acid, Sodium carbonate, , Diazolidinyl, Thymol)
• VMA (Only Boric Acid, Acetic Acid, 6NHCl, 6N HNO3)
* Boric Acid | 50% Acetic Acid | Toluene |
Sodium carbonate | 6N HCl | 6N HNO3| Diazolidinyl | Thymol

23. * Source from Mayo Clinic