Urinalysis is a diagnostic physical, chemical, and microscopic examination ofa urine sample (specimen). Specimens can be obtained by normal emptying of the bladder (voiding) or by a hospital procedure called catheterization.
Urinalyses are performed for several reasons:
- General evaluation of health.
- Diagnosis of metabolic or systemic diseases that affect kidneyfunction.
- Diagnosis of endocrine disorders. Twenty-four-hour urinestudies are often ordered for these tests.
- Diagnosis of diseases ordisorders of the kidneys or urinary tract.
- Monitoring of patients with diabetes.
- Testing for pregnancy.
- Screening for drug abuse.
Urinalysis should not be performed while a woman is menstruating or having avaginal discharge. A woman who must have a urinalysis while she has a vaginaldischarge or is having her period should insert a fresh tampon before beginning the test. She should also hold a piece of clean material over the entrance to her vagina to avoid contaminating the specimen.
Patients do not have to fast or change their food intake before a urine test.They should, however, avoid intense athletic training or heavy physical workbefore the test because it may result in small amounts of blood in the urine.
The following drugs can affect urinalysis results. The patient may be asked to stop taking them until after the test:
- Nitrofurantoin (Macrodantin,Furadantin). Nitrofurantoin is prescribed for infections of the urinary tractand other bacterial infections.
- Phenazopyridine (Pyridium). This medication is used to relieve burning and pain caused by urinary-tract infections.
- Rifampin (Rifadin). This medication is prescribed to treat tuberculosis, prevent the spread of meningitis, and treat other infections.
Bladder catheterization is sometimes used to collect urine samples from hospitalized patients. It should not, however, be used to collect specimens from males with acute inflammation of the prostate or from a patient of either sexwith a fractured pelvis.
Collecting a urine sample from emptying the bladder takes about two or threeminutes. The sample can be collected at home as well as in a doctor's office.Urine specimens are usually collected early in the morning before breakfast.Urine collected eight hours after eating and at least six hours after the most recent urination is more likely to indicate abnormalities. Some people maybe asked to void into a clean container before getting out of bed in the morning.
The doctor or hospital will supply a sterile container for a specimen being collected for a colony count. A colony count is a test that detects bacteria in urine that has been cultured for 24-48 hours. It is used instead of a routine urinalysis when a patient's symptoms suggest a urinary tract infection. Nonsterile containers can be used for routine specimens that will not be testedimmediately after being collected. An ordinary open-necked jar may be used after it and its lid have been soaked in very hot water for 15-20 minutes andthen air-dried.
Urine specimens should not remain unrefrigerated for longer than two hours. Aurine specimen that cannot be delivered to a laboratory within two hours should be stored in a refrigerator. The reason for this precaution is that urinesamples undergo chemical changes at room temperature. Blood cells begin to dissolve and the urine loses its acidity.
A doctor, nurse, or laboratory technician will look at the specimen to see ifthe urine is red, cloudy, or looks unusual in any way. He or she will also note any unusual odor.
Urine samples are tested with a variety of different instruments and techniques. Some tests use dipsticks, which are thin strips of plastic that change color in the presence of specific substances. Dipsticks can be used to measurethe acidity of the urine (its pH) or the presence of blood, protein, sugar, or substances produced during the breakdown of fatty acids (ketones). A urinometer is used to compare the density of the urine specimen with the density ofplain water. This measurement is called specific gravity.
The urine specimen is also examined under a microscope to determine whether it contains blood cells, crystals, or small pieces of fibrous material (casts).
Most urine specimens from adults or older children are collected by the patient's voiding into a suitable container. Soaps and disinfectants may contaminate urine specimens and should not be used. The doctor or laboratory may supply a special antiseptic solution that won't irritate the skin. The method forcollection varies somewhat according to age and sex.
Before collecting a urine sample, a woman or girl should use a clean cotton ball moistened with lukewarm water to cleanse the external genital area. Gently separating the folded skin (labia) on either side of her vagina, she shouldmove the cotton ball from the front of the area to the back. After repeatingthis process several times, using a fresh piece of cotton each time, she should dry the area with a clean towel.
To prevent menstrual blood, vaginal discharge, or germs from the external genitalia from contaminating the specimen, a woman or girl should release some urine before she begins to collect her sample. A urine specimen obtained thisway is called a midstream clean catch.
A man or boy should use a piece of clean cotton, moistened with antiseptic, to cleanse the head of his penis and the passage through which urine leaves his body (the urethral meatus). He should draw back his foreskin if he has notbeen circumcised. He should move the cotton in a circular motion away from the urinary opening, using a fresh piece of cotton each time. After repeating this process several times, he should use a fresh piece of cotton to remove the antiseptic. After the area has been thoroughly cleansed, he should begin urinating and collect a small sample in a container without interrupting the stream of urine.
A parent, nurse, or doctor should cleanse the child's genitals and as much ofthe surrounding area as will fit into the sterile urine-collection bag provided by the hospital. When the area has been thoroughly cleansed, the bag should be attached to the child's genital area and left in place until the childhas urinated. It is important to remember not to touch the inside of the bagand to remove it as soon as a specimen has been obtained.
Bladder catheterization is a hospital procedure used to collect uncontaminated urine when the patient cannot void. A catheter is a thin flexible tube thatthe doctor inserts through the urethra into the bladder to allow urine to flow out. To minimize the risk of infecting the patient's bladder with bacteria, many doctors use a so-called Robinson catheter, which is a plain rubber orlatex tube that is removed as soon as the specimen is collected.
Suprapubic bladder aspiration is a technique that is sometimes used to collect urine from infants younger than six months. The doctor withdraws urine fromthe bladder into a syringe through a needle inserted through the skin over the bladder. This technique is used only when the child cannot void because ofan abnormal urethra or if he or she has a urinary tract infection that has not responded to treatment.
Normal urine is a clear straw-colored liquid. It has a slight odor. It contains some crystals, a small number of cells from the tissues that line the bladder, and transparent (hyaline) casts. Normal urine does not contain sugars, yeast cells, protein, ketones, bacteria, or parasitic organisms.
The time of day a urine sample is collected can make a difference in the appearance of the specimen. Some foods and medicines, including red beets, asparagus, and penicillin, can affect the color or smell of urine. Although most color variations are harmless, they sometimes indicate the presence of seriousdisease. A doctor, nurse, or laboratory technician should be notified if theurine is red or cloudy or looks unusual in any way.
Urine may be cloudy (turbid) because it contains red or white blood cells, bacteria, fat, mucus, digestive fluid (chyle), or pus from a bladder or kidneyinfection.
Foul-smelling urine is a common symptom of urinary-tract infection. A fruityodor is associated with diabetes mellitus, starvation and dehydration, or ketone formation. Other distinctive odors are present in the urine of patients with maple syrup urine disease or phenylketonuria (PKU).