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Urine Specimens – An Overview (Part 1)

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This Focus Topic is the first of a two part series on urine specimen collection. Part 2 will cover sources of preanalytical artifact arising during urine collection, handling and transportation.

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. Urine testing, using both automated and traditional manual methods, is growing rapidly.1 As with all clinical laboratory specimens, preanalytical error in urine specimens is often difficult to detect. Because of this, it is important for laboratories to have processes in place to ensure compliance with best practice in specimen collection, handling and transport – including the use of preservatives where appropriate.

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.

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.

Timed Collection Specimens may be required for 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.

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.

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.

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.

 

Urine Collection Devices

An extensive array of urine collection products is available on the market. Information on features, intended use and instructions for use should be obtained from the device manufacturer and reviewed before being incorporated into a specimen collection protocol.

Urine Collection Containers (cups for collection and transport)

Urine collection container cups are available in a variety of shapes and sizes with lids that are either ‘snap-on’ or ‘screw-on’. Leakage is a common problem with low quality products. To protect healthcare workers from exposure to the specimen and protect the specimen from exposure to contaminants, leak-proof cups should be utilized. Some urine specimen containers have closures with special access ports that allow closed-system transfer of urine directly from the collection device to the tube  (further information)

Urine Collection Containers for 24-hour Collection

Urine collection containers for 24-hour specimens commonly have a 3 liter capacity. As for the urine collection cups above, closure types vary with some containers featuring an integrated port for transfer of an aliquot of the specimen to an evacuated urine collection tube (further information). This provides the option for the laboratory to receive only the aliquot tube and specimen weight (with the large 24-hour container and contents discarded at the point of collection). Additional precautions need to be taken when a preservative is required (further information).

Urine Specimen Tubes

Urine specimens may be poured directly into tubes with ‘screw-on’ or ‘snap-on’ caps. Additionally,evacuated tubes, similar to those used in blood collection, are available. (further information)

 

Urine Specimen Collection and Transportation Guidelines

As for any type of clinical laboratory specimen, certain criteria for collection and transportation (further information) of urine specimens must be met to ensure high quality specimens free of preanalytical artifact are obtained consistently. Without this, accurate test results cannot be guaranteed.

 

Urine Specimen Preservation

For urinalysis and culture and sensitivity testing, CLSI Guidelines2 recommend testing within two hours of collection. Different time limits may apply to specimens required for molecular testing of infectious agents (e.g. testing for Neisseria gonorrhoeae, Chlamydia trachomatis). For this type of testing, laboratories should ensure they are able to comply with specimen transportation conditions prescribed by the assay manufacturers. Where compliance with these and/or CLSI recommendations is not possible,consideration should be given to the use of a preservative (further information). Specimen collection tubes with preservatives for chemical urinalysis (further information) and culture and antibiotic susceptibility are available (further information).

 

Urine Specimen Reception in the Laboratory

In addition to routine checks and precautions taken for all specimens received in the clinical laboratory, the following additional ‘check items’ apply to urine specimens.

Labels 

Volume

Collection Date and Time

Collection Method

Specimen Preservation

Light Protection


References

  1. Frost and Sullivan Research Service. Global in vitro diagnostic market outlook. San Antonio (TX): Frost and Sullivan; 2005.
  2. Clinical and Laboratory Standards Institute (CLSI; formerly NCCLS). Urinalysis and Collection, Transportation, and Preservation of Urine Specimens; Approved Guideline – Second Edition. Vol. 21. No. 19. Document GP-16A2. Wayne, PA 2001.
  3. Journal of Clinical Microbiology, Evaluation of Liquid and Lyophilized Preservatives for Urine Culture. 1983 (Oct): 912-916.

Randomly Collected Specimens

Randomly collected specimens are suitable for urinalysis in the clinical chemistry laboratory and for microscopic analysis. However, they 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. In this situation, analyte values may be artificially low. Of necessity, pediatric urine specimens for urinalysis and microscopy are often of this type.

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First Morning Specimen is the Specimen

First morning specimens are the specimen of choice for urinalysis and microscopic analysis since the urine is generally more concentrated (due to the length of time the urine is allowed to remain in the bladder) and, therefore, contains relatively higher levels of cellular elements and analytes. Abnormal constituents are also likely to be present in higher concentration and, thus, more likely to be detected.

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Midstream Clean Catch Specimens

Midstream specimens are strongly recommended for microbiological culture and antibiotic susceptibility testing because of the reduced incidence of cellular and microbial contamination. Following instruction from a healthcare professional, patients are required to follow a prescribed procedure commencing with cleansing the urethral area. The patient should then void the first portion of the urine stream into the toilet. These first steps significantly reduce the opportunities for contaminants to enter the urine stream during collection of the clinical specimen. The urine midstream is then collected into a clean container after which the remaining urine is voided into the toilet. This method of collection can be conducted at any time of day or night.

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Timed Collection Specimens 

Timed specimens may be required for 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. A timed collection allows measurement of the excretion of these substances in urine over a specified length of time, usually, but not always, 8 or 24 hours. In this collection method, the bladder is emptied prior to beginning the timed collection. Then, for the duration of the designated time period, all urine is collected and pooled into a collection container, with the final collection taking place at the very end of that period. Half an hour before the end of the collection period, it is helpful to ask the patient to drink a glass of water, so that the last urine specimen can be obtained. If no specimen is produced, then the total volume and time of collection cannot be determined.  It is also important to caution the patient not to lose urine specimens to the toilet during defecation.   When a 24-hour urine specimen is required for the assay of catecholamines, metanephrines and/or VMA, for the diagnosis of pheochromocytoma, which causes persistent or episodic hypertension, it is advisable to monitor the blood pressure of the patient and collect the urine specimen when the blood pressure is high, in order to improve the chance of a positive finding. 

Timed specimens should be refrigerated during the collection period, unless otherwise directed by the laboratory. Accurate timing is very important as this information forms a critical part of the calculations performed to determine urine clearance values (e.g. creatinine clearance). Interpretations based on faulty calculations can result in improper diagnoses or medical treatment.

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Collection from Catheters

Urine specimens can be collected 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.

Direct draw adaptor for urine specimen collection from Foley catheter

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Supra-pubic Aspiration

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. This procedure involves collection of the specimen by needle aspiration through the abdominal wall into the bladder.

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Pediatric Specimens

Urine collection from pediatric patients presents many challenges.  For infants and small children, a special urine collection bag can be adhered to the skin surrounding the urethral area. Once the collection is completed, the urine is poured into a collection cup or transferred directly into an evacuated tube with a transfer straw. Urine collected from a diaper is not recommended for laboratory testing since contamination from the diaper material may affect test results.

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Urine Collection Containers

 

Urine collection containers with integrated port for transfer of specimen to evacuated urine collection tube

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24 Hour Urine Collection Container

24 hour urine collection container with integrated port for transfer of specimen to evacuated urine collection tube. This provides the option for the laboratory to receive only the aliquot tube and specimen weight (with the large 24-hour container and contents discarded at the point of collection).

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Preservatives for 24 Hour Specimens

When a preservative is required, it should be added to the collection container before the urine collection begins. Commonly used preservatives for 24 hour specimens are hydrochloric acid, boric acid, acetic acid, thymol and toluene. If more than one acceptable preservative is available for the analyte(s) being tested, the least hazardous one should, of course, be selected. Appropriate warning labels should be placed on the container to alert patients to possible harm arising from contact with the preservatives. This should be reinforced by appropriate instruction from the attending healthcare worker. A corresponding Material Safety Data Sheet (MSDS) should also be provided for the patient.

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Urine Specimen Tubes

Evacuated tubes, similar to those used in blood collection, are available for urine collection. These can be filled using a straw device, from urine specimen containers with integrated transfer devices, or from direct sampling devices that are used to access catheter sampling ports.

Urine transfer ‘straw’ with adaptor for transfer of specimen to evacuated urine collection tube

   

Urine collection containers with integrated port for transfer of specimen to evacuated urine collection tube

Urinalysis tubes ae available in a variety of shapes: conical bottom, round bottom, or flat bottom. Conical bottom tubes offer advantages for microscopic examination of urine sediment. The laboratory’s tube selection process must include consideration of centrifugation conditions and compatibility with automated instrument systems. Tube fill volumes are typically within the range of 4 to 10mL with dimensions of 13 x 75mm and 16 x 100mm.

Evacuated urine specimen collection tubes

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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.
  • The container material should not leach interfering substances into the specimen.
  • Specimen containers must not be re-used.
  • Specimen tubes should be compatible with automated systems and instruments used by the laboratory.
  • Collection containers and/or specimen tubes should be compatible with pneumatic tube systems where these are used for urine specimen transport. Use of leak-proof containers is essential in this situation.

The CLSI Guidelines2 makes the following recommendations for urine collection:

  • Primary (routine) specimen containers to have a wide base and a capacity of at least 50 mL.
  • 24 hour specimen containers to have a capacity of at least 3 litres.
  • Sterile collection containers for all microbiology specimens
  • Specimen containers to have secure closures to prevent specimen loss and to protect the specimen from contaminants.
  • Amber colored containers for specimens required for assay of light sensitive analytes such as urobilinogen and porphyrins.

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Urine Tubes Preservatives

For chemical urinalysis and conventional (culture based) microbiological testing, unpreserved specimens exceeding the two hour limit that have not been refrigerated should not be accepted for analysis due to potential bacterial overgrowth leading to disintegration of cells and casts*, invalidation of bacterial colony counts and errors in chemical urinalysis. When specimens for such testing are directly transferred from a collection cup to a tube containing a suitable preservative, a stable environment is provided for the specimen until testing can be conducted. Preservatives are also available for some molecular tests (e.g. BD UPT urine specimen tube for use with BD ProbeTec™ ET assay system) .  When a decision to use a preservative is made – for any type of testing, potential interference with assay methods should be considered. Laboratories should validate all test procedures intended to be used for preserved specimens. Specimens may need to be split if various tests requiring different preservatives are requested.

* Bacterial growth increases the pH of the urine leading to lysis of red blood cells and white blood cells.  Increased pH (alkalinity) can also cause casts to dissolve.

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Chemical Urinalysis Preservatives

A variety of urine preservatives is available that allow urine to be maintained at room temperature while still providing urinalysis test results comparable to those achieved with fresh specimens or those stored under refrigerated conditions. Commonly used preservatives for chemical urinalysis specimens include tartaric acid, boric acid, chlorhexidine, ethyl paraben, thymol and sodium propionate (and ‘cocktails’ of these). Preservation times are typically within the range of 24 to 72 hours. Claims for the duration of stability for specific analytes should be obtained from the manufacturer.

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Culture and Antibiotic Susceptibility Preservatives

Preservatives for culture and antibiotic susceptibility testing are designed to maintain the specimen in a state equivalent to that which would be achieved with refrigeration by deterring the proliferation of organisms that could result in a false positive culture or bacterial overgrowth. Careful attention must be given to the formulation of these preservatives to achieve this objective. There is evidence to suggest that non-pH buffered boric acid may be harmful to certain organisms and that buffered boric acid preservatives can reduce the harmful effects of the preservative on the organisms3. Preserved urine specimens can be stored at room temperature until the time of testing. Product claims regarding duration of preservative potency should be obtained from the manufacturer.

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Labels

If the collection container is used for transport, the label should be placed on the container and not on the lid, since the lid can be mistakenly placed on a different container. Note that some labels are unsuitable for specimens stored under refrigerated conditions because of a lack of adhesion at low temperatures.

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Volume

It is important for specimen collection personnel to ensure there is sufficient volume to perform the required tests. For specimens in preservative tubes, the fill volume must be correct. As above, under-filling or over-filling these tubes may adversely affect test result accuracy.

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Collection Time and Date

Collection time and date must be shown on the specimen label. For timed specimens, both the start and stop times of the collection must be shown. The time at which the specimen was received in the laboratory must also be documented for verification of proper handling and transport after collection.

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Collection Method

The method of collection should be confirmed when the specimen is received in the laboratory to ensure the type of specimen submitted meets the needs of the required test(s). An example of an optimum specimen/test match would be a first morning specimen for urinalysis and microscopic examination.

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Specimen Preservation

If the specimen is not received within two hours of collection, specimen reception personnel must confirm that a tube containing an appropriate preservative has been used. Confirmation that the specimen is received within the allowable time for the particular preservative tube used is required.

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Light Protection

Specimens submitted for testing of light-sensitive analytes must be collected in containers that protect the specimen from light.

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Last modification on 15th November 2012

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