LabNotes - Volume 14, No.2, 2004

The Basics of Specimen Collection and Handling of Urine Testing

The First in a Two-Part Series
Catherine Skobe, MT (ASCP)

Urine has a long, rich history as a source for measuring health and well-being and remains an important tool for clinical diagnosis. The clinical information obtained from a urine specimen is influenced by the collection method, timing and handling. A vast assortment of collection and transport containers for urine specimens are available. Determining which urine collection method and container should be used depends on the type of laboratory test ordered.

[Color photo of urine collection system]Types of Collection

Laboratory urine specimens are classified by the type of collection conducted or by the collection procedure used to obtain the specimen.

Random Specimen This is the specimen most commonly sent to the laboratory for analysis, primarily because it is the easiest to obtain and is readily available. This specimen is usually submitted for urinalysis and microscopic analysis, although it is not the specimen of choice for either of these tests. Random specimens can sometimes give an inaccurate view of a patient's health if the specimen is too diluted and analyte values are artificially lowered. Pediatric specimens, which routinely undergo chemistry and microscopic analysis, are generally of this type. As the name implies, the random specimen can be collected at any time. Although there are no specific guidelines for how the collection should be conducted, avoiding the introduction of contaminants into the specimen is recommended. This requires explicit instructions to patients so that they do not touch the inside of the cup or cup lid.

First Morning Specimen This is 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 such as protein, if present. Also called an 8-hour specimen, the first morning specimen is collected when the patient first wakes up in the morning, having emptied the bladder before going to sleep. Since the urine can be collected over any eight-hour period, collection is practical for patients who have atypical work/sleep schedules. Proper collection practices and accurate recording of the collection time are important criteria of a first morning specimen. Note: Any urine that is voided from the bladder during the eight-hour collection period should be pooled and refrigerated, so that a true 8-hour specimen is obtained.

Midstream Clean Catch Specimen This is the preferred type of specimen for culture and sensitivity testing because of the reduced incidence of cellular and microbial contamination. Patients are required to first cleanse the urethral area with a castile soap towelette. 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 into the urine stream. The urine midstream is then collected into a clean container (any excess urine should be voided into the toilet). This method of collection can be conducted at any time of day or night.

Timed Collection Specimen Among the most commonly performed tests requiring timed specimens are those measuring creatinine, urine urea nitrogen, glucose, sodium, potassium, or analytes such as catecholamines and 17-hydroxysteroids that are affected by diurnal variations.

[Graphic of an alarm clock]A timed specimen is collected to measure the concentration of these substances in urine over a specified length of time, usually 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. The specimen should be refrigerated during the collection period, unless otherwise requested by the physician. Accurate timing is critical to the calculations that are conducted to determine analyte concentrations and ratios. Interpretations based on faulty calculations can result in improper diagnoses or medical treatment.

Catheter Collection Specimen This assisted procedure is conducted when a patient is bedridden or cannot urinate independently. The healthcare provider inserts a foley catheter into the bladder through the urethra to collect the urine specimen. (Specimens may also be collected through an existing foley catheter.) Specimens may be collected directly from a foley into an evacuated tube or transferred from a syringe into a tube or cup.

Suprapubic Aspiration Specimen This method is used when a bedridden patient cannot be catheterized or a sterile specimen is required. The urine specimen is collected by needle aspiration through the abdominal wall into the bladder.

Pediatric Specimen For infants and small children, a special urine collection bag is 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.

Urine Collection Products

There are many different manufacturers of urine collection containers. Information on a specific product's uses, features and claims should be obtained from that device's manufacturer.

[Color photo of a urine collection cup]Urine Collection Containers (cups for collection and transport) Urine collection container cups come in a variety of shapes and sizes with lids that are either snap on or screw on. To protect healthcare personnel from exposure to the specimen and protect the specimen from exposure to contaminants, leak-resistant cups should be utilized. Some urine transport cup closures have special access ports that allow closed-system transfer of urine directly from the collection device to the tube.

Urine Collection Containers (24-hour collection) Urine collection containers for 24-hour specimens come in a variety of shapes and colors, but most are of 3 liter (L) capacity1 and are amber colored (to protect light-sensitive analytes such as porphyrins and urobilinogen). Closure types vary and some have a port for ease of specimen transfer into a tube. When a preservative is required, it should be added to the collection container before the urine collection begins and warning labels should be placed on the container. If there is more than one acceptable preservative for the analyte being tested, the least hazardous one should be selected. A corresponding Material Safety Data Sheet (MSDS) should be given to the patient, and the healthcare provider should explain any potential hazards. Some common 24-hour preservatives are hydrochloric acid, boric acid, acetic acid and toluene.

Urinalysis Tubes Urine specimens are poured directly into urinalysis tubes with screw- or snap-on caps. Additionally, there are evacuated tubes similar to those used in blood collection that are filled by using a straw device, from cups with integrated transfer devices built into their lid, or from direct sampling devices that are used to access catheter sampling ports. Urinalysis tubes come in an array of tube shapes: conical bottom, round bottom, or flat bottom. Conical bottom tubes provide the best sediment collection for microscopic analysis. Some tubes are specially designed to be used with a pipetter that allows for standardized sampling. The tubes you select should be able to withstand centrifugation and, if used with an automated instrument system, should be compatible with the corresponding racks and carriers. Fill volumes of urinalysis tubes usually range from 8 to 15 mL.

Preservatives for Urinalysis NCCLS Guidelines recommend testing urine within two hours of its collection. However, refrigeration or chemical preservation of urine specimens may be utilized if testing or refrigeration within a two-hour window is not possible. A variety of urine preservatives (tartaric and boric acids being the most common) are available that allow urine to be kept at room temperature while still providing results comparable to those of refrigerated urine. Generally, the length of preservation capacity ranges from 24 to 72 hours. Claims for the length of specific analyte preservation should be obtained from the manufacturer. When a specimen is directly transferred from a collection cup into a preservative tube, it provides a stable environment for the specimen until testing can be conducted and reduces the risk of bacterial overgrowth or specimen decomposition. Non-additive tubes (those not containing any chemical preservatives) can be used for urinalysis, but must be handled following strict timing and refrigeration guidelines.

Preservatives for Culture and Sensitivity (C&S) Testing The most common preservative used for culture and sensitivity is boric acid, which comes in tablet, powder or lyophilized form.

There is clinical evidence to suggest that non-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 organisms.2 C&S preservatives are designed to maintain the specimen in a state equivalent to refrigeration by deterring the proliferation of organisms that could result in a false positive culture or bacterial overgrowth. Preserved urine specimens can be stored at room temperature until time of testing. Product claims regarding duration of preservative potency should be obtained from the particular manufacturer.

Specimen Collection and Transport Guidelines

As with any type of laboratory specimen, there are certain criteria that need to be met for proper collection and transportation of urine specimens. This will ensure proper stability of the specimen and more accurate test results.

  • 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-resistent. Leak-resistent containers reduce specimen loss and healthcare worker exposure to the specimen while also protecting the specimen from contaminants.
  • It is good practice to use containers that are made of break-resistant plastic, which is safer than glass.
  • The container material should not leach interfering substances into the specimen.
  • Specimen containers should not be reused.
  • The NCCLS guidelines for urine, GP-16A2, recommend the use of a primary collection container that holds at least 50 mL, has a wide base and an opening of at least 4 cm.1 The wide base prevents spillage and a 4 cm opening is an adequate target for urine collection. The 24-hour containers should hold up to 3L.1
  • The NCCLS guidelines recommend sterile collection containers for microbiology specimens.1 The containers should have secure closures to prevent specimen loss and to protect the specimen from contaminants.
  • Transport tubes should be compatible with automated systems and instruments used by the lab.
  • Collection containers and/or transport tubes should be compatible with the pneumatic tube system if one is used for urine specimen transport in the facility. A leak-proof device in this situation is critical.
  • NCCLS recommends the use of an amber colored container for specimens being assayed for light sensitive analytes, such as urobilinogen and porphyrins.1 The colorant prevents the degradation of certain analytes.
  • Proper labeling should be applied to the collection container or tubes.

Specimen Preservation Guidelines

  • NCCLS guidelines for microbiological urine testing recommend the use of chemical preservatives if the specimen cannot be processed within 2 hours of collection. Otherwise, these specimens should be refrigerated at 2-8°C.1 For urinalysis, NCCLS recommends the evaluation of urine preservation systems by the laboratory before being utilized in the facility.1
  • The proper specimen-to-additive ratio must be maintained when using a chemical preservative to ensure accurate test results. Maintaining the correct ratio is especially important when transferring samples into a preservative tube. Use the indicated fill lines on the tube to ensure proper fill. Underfilling the tube will leave a high concentration of preservative in the specimen, while overfilling the tube will overly dilute the preservative. In either case, the function of the preservative may be compromised.
  • An evacuated tube system is designed to achieve proper fill volume to ensure the proper specimen-to-additive ratio and proper preservative function. Evacuated systems also reduce the potential exposure of the healthcare worker to the specimen.
  • Chemical preservatives should be non-mercuric and environmentally friendly.
  • The EPA cites mercuric oxide used in urinalysis preservatives as a source of mercury in medical laboratories. The American Hospital Association and the EPA have issued a Memorandum of Understanding for the "virtual elimination of mercury containing waste from the health care industry waste stream" by the year 2005.3 Certain states have already established a zero tolerance mandate for mercury waste generation and improper disposal. The EPA website, http://www.epa.gov/mercury offers additional information on mercury that is pertinent to medical environments and safety.

Urine Specimen Handling Guidelines

Labels Include the patient name and identification on labels. Make sure that the information on the container label and the requisition match. 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. Ensure that the labels used on the containers are adherent under refrigerated conditions.

Volume Ensure that there is sufficient volume to fill the tubes and/or perform the tests. Underfilling or overfilling containers with preservatives may affect specimen-to-additive ratios.

Collection Date and Time Include collection time and date on the specimen label. This will confirm that the collection was done correctly. For timed specimens, verify start and stop times of collection. Document the time at which the specimen was received in the laboratory for verification of proper handling and transport after collection.

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

Proper Preservation Check if there is a chemical preservative present or if the specimen has not been refrigerated for greater than two hours post collection. After accepting the test request, ensure that the method of preservation used is appropriate for the selected test. If the correct preservative was not used the test cannot be conducted.

Light Protection Verify that specimens submitted for testing of light-sensitive analytes are collected in containers that protect the specimen from light. This is a glimpse into the complexity of proper urine collection and handling. Since a variety of urine collection procedures and applications exist today, it becomes critical to understand how, when and where things can go wrong. As the trend toward more home-based testing and less invasive methods continues, urine will become one of the most useful specimen types collected for clinical assessment.

References:

  1. NCCLS GP-16A2, Volume 21, No. 19, Urinalysis and Collection, Transportation, and Preservation of Urine Specimens; Approved Guideline-Second Edition, p. 4-21.
  2. Journal of Clinical Microbiology, Oct. 1983, Evaluation of Liquid and Lyophilized Preservatives for Urine Culture, p.912-916.
  3. Memorandum of Understanding Between the United States Environmental Protection Agency and the American Hospital Association, Created July 30, 1998, Sec. 3.2.

 

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