Urine formation and specimen collection

Urinalysis

Urine is the second most common specimen analyzed in the laboratory. Only blood is tested more frequently. Urine is analyzed for several reasons:

• To detect diseases or disorders in which the kidneys are working normally but are excreting abnormal substances that are the result of an imbalance of homeostasis in the body. For example, an individual with diabetes mellitus may be excreting glucose.
• To detect diseases or disorders of the kidneys or urinary tract. Examples would be the presence of kidney stones or a urinary tract infection (UTI).
• To detect medications or drugs that are excreted by the kidneys.

Urine formation and elimination

Medical assistants must have a basic knowledge of kidney structure and urine formation to understand the results of a urinalysis (UA).

Formation of urine

The urinary tract consists of two kidneys, two ureters, one bladder, and one urethra. Blood passes through microscopic structures in the kidneys called nephrons. In the nephrons, blood is filtered to form a filtrate. The composition of the filtrate is adjusted as it passes through the renal tubules of the nephron. Selective reabsorption and secretion occur in the renal tubules until the filtrate reaches its final composition. The final filtrate is known as urine.

Elimination of urine

Urine flows through a series of collection areas until it leaves the kidney through the ureter and is stored in the urinary bladder. Urine remains in the bladder until it is voided through the urethra. The average person voids about 1 to 2 liters of urine per day.

The largest component of urine is water. Normal waste products found in urine include urea, uric acid, creatinine, and electrolytes (sodium, chloride, potassium). Abnormal waste products that can be found in urine include protein, glucose, ketones, red blood cells (RBCs), white blood cells (WBCs), bacteria, nitrites, bilirubin, and urobilinogen. Protein and blood cells are too large to be filtrated by the glomerulus, so when these substances appear in the urine, it may indicate damage to one or more organs of the urinary system.

Collecting and handling of a urine specimen

The request for a urine specimen may create an uneasy moment for the patient. The request should be made in a private area, such as the exam room, if possible. The patient should be given clear instructions so that he or she understands what is expected. The medical assistant should clearly communicate and explain the details of the procedure.

Be observant and ask the patient to repeat the directions, so you know he or she understands the procedure. Answer any questions with patience and clear directions to avoid confusion. If a language barrier exists, be creative but respectful of the patient’s needs. Use an interpreter if one is available. Posting a picture with directions in a variety of languages in the patient restroom could also help.

There are a few specimens on the counter, and Julie asks Becca if she has practiced giving instructions for UA collection procedures in any of her classes. Becca replies that she has but thought it was a bit silly. Julie talks about how patients can be embarrassed about collecting specimens and may not want to ask too many questions. Julie asks Becca to write down three items that are important to include when explaining a UA collection procedure. Write down your own answer and be ready to share it with your class.

Containers

The POL should provide the appropriate urine container for the patient. Patients should not use containers from home. Disposable, non sterile, plastic, or coated paper containers are the most frequently used and are available in many sizes with tight-fitting lids. Most routine UA tests, pregnancy tests, and tests for abnormal analytes are performed on urine collected in non sterile containers. Special flexible polyethylene bags with adhesive are used to collect urine from infants and children who are not toilet trained. For specimens that must be collected over a stated time (24-hour urines), large, wide-mouth plastic containers with screw-cap tops are used.

If the sample is being sent to the microbiology department of the laboratory for culture, it must be collected in a sterile container. Explain the collection procedure to the patient, and make sure the patient understands how to collect the specimen and handle the sterile specimen cup. Most sterile containers have a paper seal over the cap. If the seal is broken, the specimen cup may not be sterile and should be discarded.

Labeling

The label on all specimens must be printed in permanent marker or ink and include the patient’s name, the date and time of collection, and the type of specimen. If available, computer-generated labels should be placed on the container so that the information is easy to read. Always put on gloves before handling filled specimen containers.

When a clinic sends specimens to multiple laboratories, it is important to have a system in place that meets the labeling and collection needs of all facilities. Each laboratory may require specific information and specific specimen containers. Double-check the laboratory name and specimen requirements before patient collection to avoid mistakes and possible specimen recollection issues. Patient insurance may direct laboratory usage or affiliation.

Methods of specimen collection

There are several types of urine specimens:

• Random specimen: Urine is collected in clean containers. Most tests use this type of specimen.
• First-morning specimen: A urine specimen is collected when the patient first wakes up in the morning. This type of specimen is more concentrated than a random sample. It is best used when testing for nitrite, protein, or pregnancy and microscopic examination. First-morning samples are also the preferred samples for possible UTI testing, but this is not a requirement. • Second-voided specimen: The first void of the morning is discarded, and the second void of the day is collected for testing. The specimen is used to determine glucose levels in urine.
• Two-hour postprandial urine specimens: The specimen is collected 2 hours after a meal. This specimen is required for diabetes screening and home diabetes testing programs.
• Catheterized specimen: The provider, nurse, or specially trained medical assistant inserts a sterile catheter into the bladder to collect the specimen.
• Besides these specimens, a 24-hour specimen collection and a clean-catch midstream specimen collection can also be required. The following sections describe these two collection methods.