Urinalysis

Definition

A urinalysis is a group of manual and/or automated qualitative and semi-quantitative tests performed on a urine sample. A routine urinalysis usually includes the following tests: color, transparency, specific gravity, pH, protein, glucose, ketones, blood, bilirubin, nitrite, urobilinogen, and leukocyte esterase. Some laboratories include a microscopic examination of urinary sediment with all routine urinalysis tests. If not, it is customary to perform the microscopic exam, if transparency, glucose, protein, blood, nitrite, or leukocyte esterase is abnormal.

Purpose

Routine urinalyses are performed for several reasons:

• general health screening to detect renal and metabolic diseases
• diagnosis of diseases or disorders of the kidneys or urinary tract
• monitoring of patients with diabetes

In addition, quantitative urinalysis tests may be performed to help diagnose many specific disorders, such as endocrine diseases, bladder cancer, osteoporosis, and porphyrias (a group of disorders caused by chemical imbalance). Quantitative analysis often requires the use of a timed urine sample. The urinary microalbumin test measures the rate of albumin excretion in the urine using laboratory tests. This test is used to monitor the kidney function of persons with diabetes mellitus. In diabetics, the excretion of greater than 200 μg/mL albumin is predictive of impending kidney disease.

Precautions

Voided specimens

All patients should avoid intense athletic training or heavy physical work before the test, as these activities may cause small amounts of blood to appear in the urine. Many urinary constituents are labile, and samples should be tested within one hour of collection or refrigerated. Samples may be stored at 36–46°F (2–8°C) for up to 24 hours for chemical urinalysis tests; however, the microscopic examination should be performed within four hours of collection, if possible. To minimize sample contamination, women who require a urinalysis during menstruation should insert a fresh tampon before providing a urine sample.

Over two dozen drugs are known to interfere with various chemical urinalysis tests. These include:

• ascorbic acid
• chlorpromazine
• L-dopa
• nitrofurantoin (Macrodantin, Furadantin)
• penicillin
• phenazopyridine (Pyridium)
• rifampin (Rifadin)
• tolbutamide

The preservatives that are used to prevent loss of glucose and cells may affect biochemical test results. The use of preservatives should be avoided whenever possible in urine tests.

Description

Routine urinalysis consists of three testing groups: physical characteristics, biochemical tests, and microscopic evaluation.

Physical tests

The physical tests measure the color, transparency (clarity), and specific gravity of a urine sample. In some cases, the volume (daily output) may be measured. Color and transparency are determined from visual observation of the sample.

color. Normal urine is straw yellow to amber in color. Abnormal colors include bright yellow, brown, black (gray), red, and green. These pigments may result from medications, dietary sources, or diseases. For example, red urine may be caused by blood or hemoglobin, beets, medications, and some porphyrias. Black-gray urine may result from melanin (melanoma) or homogentisic acid (alkaptonuria, a result of a metabolic disorder). Bright yellow urine may be caused by bilirubin (a bile pigment). Green urine may be caused by biliverdin or certain medications. Orange urine may be caused by some medications or excessive urobilinogen (chemical relatives of urobilinogen). Brown urine may be caused by excessive amounts of prophobilin or urobilin (a chemical produced in the intestines).

transparency. Normal urine is transparent. Turbid (cloudy) urine may be caused by either normal or abnormal processes. Normal conditions giving rise to turbid urine include precipitation of crystals, mucus, or vaginal discharge. Abnormal causes of turbidity include the presence of blood cells, yeast, and bacteria.

specific gravity. The specific gravity of urine is a measure of the concentration of dissolved solutes (substances in a solution), and it reflects the ability of the kidneys to concentrate the urine (conserve water). Specific gravity is usually measured by determining the refractive index of a urine sample (refractometry) or by chemical analysis. Specific gravity varies with fluid and solute intake. It will be increased (above 1.035) in persons with diabetes mellitus and persons taking large amounts of medication. It will also be increased after radiologic studies of the kidney owing to the excretion of x ray contrast dye. Consistently low specific gravity (1.003 or less) is seen in persons with diabetes insipidus. In renal (kidney) failure, the specific gravity remains equal to that of blood plasma (1.008–1.010) regardless of changes in the patient's salt and water intake. Urine volume below 400 mL per day is considered oliguria (low urine production), and may occur in persons who are dehydrated and those with some kidney diseases. A volume in excess of 2 liters (slightly more than 2 quarts) per day is considered polyuria (excessive urine production); it is common in persons with diabetes mellitus and diabetes insipidus.

Biochemical tests

Biochemical testing of urine is performed using dry reagent strips, often called dipsticks. A urine dipstick consists of a white plastic strip with absorbent microfiber cellulose pads attached to it. Each pad contains the dried reagents needed for a specific test. The person performing the test dips the strip into the urine, lets it sit for a specified amount of time, and compares the color change to a standard chart.

Additional tests are available for measuring the levels of bilirubin, protein, glucose, ketones, and urobilinogen in urine. In general, these individual tests provide greater sensitivity; they therefore permit detection of a lower concentration of the respective substance. A brief description of the most commonly used dry reagent strip tests follows.

pH: A combination of pH indicators (methyl red and bromthymol blue) react with hydrogen ions (H+) to produce a color change over a pH range of 5.0 to 8.5. pH measurements are useful in determining metabolic or respiratory disturbances in acid-base balance. For example, kidney disease often results in retention of H+ (reduced acid excretion). pH varies with a person's diet, tending to be acidic in people who eat meat but more alkaline in vegetarians. pH testing is also useful for the classification of urine crystals.

Protein: Based upon a phenomenon called the "protein error of indicators," this test uses a pH indicator, such as tetrabromphenol blue, that changes color (at constant pH) when albumin is present in the urine. Albumin is important in determining the presence of glomerular damage. The glomerulus is the network of capillaries in the kidneys that filters low molecular weight solutes such as urea, glucose, and salts, but normally prevents passage of protein or cells from blood into filtrate. Albuminuria occurs when the glomerular membrane is damaged, a condition called glomerulonephritis.

Glucose (sugar): The glucose test is used to monitor persons with diabetes. When blood glucose levels rise above 160 mg/dL, the glucose will be detected in urine. Consequently, glycosuria (glucose in the urine) may be the first indicator that diabetes or another hyperglycemic condition is present. The glucose test may be used to screen newborns for galactosuria and other disorders of carbohydrate metabolism that cause urinary excretion of a sugar other than glucose.

Ketones: Ketones are compounds resulting from the breakdown of fatty acids in the body. These ketones are produced in excess in disorders of carbohydrate metabolism, especially Type 1 diabetes mellitus. In diabetes, excess ketoacids in the blood may cause life-threatening acidosis and coma. These ketoacids and their salts spill into the urine, causing ketonuria. Ketones are also found in the urine in several other conditions, including fever; pregnancy; glycogen storage diseases; and weight loss produced by a carbohydrate-restricted diet.

Blood: Red cells and hemoglobin may enter the urine from the kidney or lower urinary tract. Testing for blood in the urine detects abnormal levels of either red cells or hemoglobin, which may be caused by excessive red cell destruction, glomerular disease, kidney or urinary tract infection, malignancy, or urinary tract injury.

Bilirubin: Bilirubin is a breakdown product of hemoglobin. Most of the bilirubin produced in humans is conjugated by the liver and excreted into the bile, but a very small amount of conjugated bilirubin is reabsorbed and reaches the general circulation to be excreted in the urine. The normal level of urinary bilirubin is below the detection limit of the test. Bilirubin in the urine is derived from the liver, and a positive test indicates hepatic disease or hepatobiliary obstruction.

Specific gravity: Specific gravity is a measure of the ability of the kidneys to concentrate urine by conserving water.

Nitrite: Some disease bacteria, including the lactose-positive Enterobactericeae, Staphylococcus, Proteus, Salmonella, and Pseudomonas are able to reduce nitrate in urine to nitrite. A positive test for nitrite indicates bacteruria, or the presence of bacteria in the urine.

Urobilinogen: Urobilinogen is a substance formed in the gastrointestinal tract by the bacterial reduction of conjugated bilirubin. Increased urinary urobilinogen occurs in prehepatic jaundice (hemolytic anemia), hepatitis, and other forms of hepatic necrosis that impair the circulation of blood in the liver and surrounding organs. The urobilinogen test is helpful in differentiating these conditions from obstructive jaundice, which results in decreased production of urobilinogen.

Leukocytes: The presence of white blood cells in the urine usually signifies a urinary tract infection, such as cystitis, or renal disease, such as pyelonephritis or glomerulonephritis.

Microscopic examination

A urine sample may contain cells that originated in the blood, the kidney, or the lower urinary tract. Microscopic examination of urinary sediment can provide valuable clues regarding many diseases and disorders involving these systems.

The presence of bacteria or yeast and white blood cells helps to distinguish between a urinary tract infection and a contaminated urine sample. White blood cells are not seen if the sample has been contaminated. The presence of cellular casts (casts containing RBCs, WBCs, or epithelial cells) identifies the kidneys, rather than the lower urinary tract, as the source of such cells. Cellular casts and renal epithelial (kidney lining) cells are signs of kidney disease.

The microscopic examination also identifies both normal and abnormal crystals in the sediment. Abnormal crystals are those formed as a result of an abnormal metabolic process and are always clinically significant. Normal crystals are formed from normal metabolic processes; however, they may lead to the formation of renal calculi, or kidney stones.

Preparation

A urine sample is collected in an unused disposable plastic cup with a tight-fitting lid. A randomly voided sample is suitable for routine urinalysis, although the urine that is first voided in the morning is preferable because it is the most concentrated. The best sample for analysis is collected in a sterile container after the external genitalia have been cleansed using the midstream void (clean-catch) method. This sample may be cultured if the laboratory findings indicate bacteruria.

To collect a sample using the clean-catch method:

• Females should use a clean cotton ball moistened with lukewarm water (or antiseptic wipes provided with collection kits) to cleanse the external genital area before collecting a urine sample. To prevent contamination with menstrual blood, vaginal discharge, or germs from the external genitalia, they should release some urine before beginning to collect the sample.
• Males should use a piece of clean cotton moistened with lukewarm water or antiseptic wipes to cleanse the head of the penis and the urethral meatus (opening). Uncircumcised males should draw back the foreskin. After the area has been thoroughly cleansed, they should use the midstream void method to collect the sample.
• For infants, a parent or health care worker should cleanse the baby's outer genitalia and surrounding skin. A sterile collection bag should be attached to the child's genital area and left in place until he or she has urinated. It is important to not touch the inside of the bag, and to remove it as soon as a specimen has been obtained.

Urine samples can also be obtained via bladder catheterization, a procedure used to collect uncontaminated urine when the patient cannot void. A catheter is a thin flexible tube that a health care professional 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 clinicians use a Robinson catheter, which is a plain rubber or latex tube that is removed as soon as the specimen is collected. If urine for culture is to be collected from an indwelling catheter, it should be aspirated (removed by suction) from the line using a syringe and not removed from the bag in order to avoid contamination.

Suprapubic bladder aspiration is a collection technique sometimes used to obtain urine from infants younger than six months or urine directly from the bladder for culture. The doctor withdraws urine from the bladder into a syringe through a needle inserted through the skin.

Aftercare

The patient may return to normal activities after collecting the sample and may start taking any medications that were discontinued before the test.

Risks

There are no risks associated with voided specimens. The risk of bladder infection from catheterization with a Robinson catheter is about 3%.

Normal results

Normal urine is a clear straw-colored liquid, but may also be slightly hazy. It has a slight odor, and some laboratories will note strong or atypical odors on the urinalysis report. A normal urine specimen may contain some normal crystals as well as squamous or transitional epithelial cells from the bladder, lower urinary tract, or vagina. Urine may contain transparent (hyaline) casts, especially if it was collected after vigorous exercise . The presence of hyaline casts may be a sign of kidney disease, however, when the cause cannot be attributed to exercise, running, or medications. Normal urine contains a small amount of urobilinogen, and may contain a few RBCs and WBCs. Normal urine does not contain detectable amounts of glucose or other sugars, protein, ketones, bilirubin, bacteria, yeast cells, or trichomonads. Normal values used in many laboratories are given below:

• Glucose: negative (quantitative less than 130 mg/day or 30 mg/dL).
• Bilirubin: negative (quantitative less than 0.02 mg/dL).
• Ketones: negative (quantitative 0.5–3.0 mg/dL).
• pH: 5.0–8.0.
• Protein: negative (quantitative 15–150 mg/day, less than 10 mg/dL).
• Blood: negative.
• Nitrite: negative.
• Specific gravity: 1.015–1.025.
• Urobilinogen: 0–2 Ehrlich units (quantitative 0.3–1.0 Ehrlich units).
• Leukocyte esterase: negative.
• Red blood cells: 0–2 per high power field.
• White blood cells: 0–5 per high power field (0–10 per high power field for some standardized systems).

Resources

books

Chernecky, Cynthia C, and Barbara J. Berger. Laboratory Tests and Diagnostic Procedures, 3rd ed. Philadelphia, PA: W. B. Saunders Company, 2001.

Henry, J.B. Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Philadelphia, PA: W.B. Saunders Company, 2001.

Kee, Joyce LeFever. Handbook of Laboratory and Diagnostic Tests, 4th ed. Upper Saddle River, NJ: Prentice Hall, 2001.

Wallach, Jacques. Interpretation of Diagnostic Tests, 7th ed. Philadelphia, PA: Lippincott Williams & Wilkens, 2000.

organizations

American Association of Kidney Patients. 100 S. Ashley Drive, Suite 280, Tampa, FL 33260. (800) 749-2257. <www.aakp.org>.

American Kidney Fund. 6110 Executive Blvd., Suite 1010, Rockville, MD 20852. (301) 881-3052. <www.akfinc.org>.

American Medical Technologists. 710 Higgins Road, Park Ridge, IL 60068-5765. (847) 823-5169. <www.amt1.com>.

American Society for Clinical Pathology (ASCP). 2100 West Harrison Street, Chicago, Il 60612-3798. (312) 738-1336. <www.ascp.org>.

National Kidney and Urologic Diseases Information Clearinghouse. 3 Information Way, Bethesda, MD 20892-3580.

other

National Institutes of Health. <www.nlm.nih.gov/medlineplus/encyclopedia.html> [cited April 4, 2003].

Victoria E. DeMoranville Mark A. Best

Urinalysis

Definition

Urinalysis is a diagnostic physical, chemical, and microscopic examination of a urine sample (specimen). Specimens can be obtained by normal emptying of the bladder (voiding) or by a hospital procedure called catheterization.

Purpose

Urinalyses are performed for several reasons:

• general evaluation of health
• diagnosis of metabolic or systemic diseases that affect kidney function
• diagnosis of endocrine disorders. Twenty-four hour urine studies are often ordered for these tests
• diagnosis of diseases or disorders of the kidneys or urinary tract
• monitoring of patients with diabetes
• testing for pregnancy
• screening for drug abuse

Precautions

Voided specimens

Urinalysis should not be performed while a woman is menstruating or having a vaginal discharge. A woman who must have a urinalysis while she has a vaginal discharge 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 work before 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 tract and 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

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 sex with a fractured pelvis.

Description

Collecting a urine sample from emptying the bladder takes about two or three minutes. 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 may be asked to void into a clean container before getting out of bed in the morning.

Specimen containers

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 tested immediately 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 and then air-dried.

Laboratory procedures

STORAGE. Urine specimens should not remain unrefrigerated for longer than two hours. A urine specimen that cannot be delivered to a laboratory within two hours should be stored in a refrigerator. The reason for this precaution is that urine samples undergo chemical changes at room temperature. Blood cells begin to dissolve and the urine loses its acidity.

VISUAL EXAMINATION. A doctor, nurse, or laboratory technician will look at the specimen to see if the urine is red, cloudy, or looks unusual in any way. He or she will also note any unusual odor.

TESTING TECHNIQUES. 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 measure the 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 of plain 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).

Preparation

Voided specimens

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 for collection varies somewhat according to age and sex.

WOMEN AND GIRLS. 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 should move the cotton ball from the front of the area to the back. After repeating this 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 this way is called a midstream clean catch.

MEN AND BOYS. 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 not been 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.

INFANTS. A parent, nurse, or doctor should cleanse the child's genitals and as much of the 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 child has urinated. It is important to remember not to touch the inside of the bag and to remove it as soon as a specimen has been obtained.

Bladder catheterization

Bladder catheterization is a hospital procedure used to collect uncontaminated urine when the patient cannot void. A catheter is a thin flexible tube that the 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 or latex 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 from the 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 of an abnormal urethra or if he or she has a urinary tract infection that has not responded to treatment.

Aftercare

The patient may return to normal activities after collecting the sample and may start taking medications that were discontinued before the test.

Risks

There are no risks associated with voided specimens. The risk of bladder infection from catheterization with a Robinson catheter is about 3%.

Normal results

Contents and appearance

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 serious disease. A doctor, nurse, or laboratory technician should be notified if the urine is red or cloudy or looks unusual in any way.

Acidity

The pH of normal urine is 4.5-8.0. Its specific gravity is 1.0005-1.035.

Abnormal results

Cloudiness

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 kidney infection.

Odor

Foul-smelling urine is a common symptom of urinary-tract infection. A fruity odor 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).

Specific gravity

The specific gravity of urine can be affected by a range of diseases and disorders. Low specific gravity (below 1.005) is associated with diabetes insipidus, nephrogenic diabetes insipidus, acute tubular necrosis, and inflammation of the upper urinary tract (pyelonephritis ). In fixed specific gravity, the specific gravity of the urine remains at 1.010 no matter how much fluid the person drinks. This condition occurs in patients who have chronic inflammation of the small blood vessels in the kidneys (glomerulonephritis ) and serious kidney damage. High specific gravity (above 1.035) occurs in patients who are in shock or who suffer from nephrotic syndrome, dehydration, acute glomerulonephritis, congestive heart failure, or liver failure.

pH

A pH factor greater than 7 (more alkaline) may result from Fanconi's syndrome, urinary tract infections, or metabolic or respiratory alkalosis. A pH factor below 7 (more acid) may be due to fever, PKU, the secretion of homogentisic acid in the urine (alkaptonuria), and acidosis.

Blood and tissue cells

Red blood cells in the urine can be due to vigorous exercise or exposure to toxic chemicals. Bloody urine can also be a sign of bleeding in the genitourinary tract as a result of systemic bleeding disorders, various kidney diseases, bacterial infections, parasitic infections including malaria, obstructions in the urinary tract, scurvy, subacute bacterial endocarditis, traumatic injuries, and tumors.

A high number of white blood cells in the urine is usually a symptom of urinary tract infection. A large number of cells from tissue lining (epithelial cells) can indicate damage to the small tubes that carry material into and out of the kidneys.

Casts

Casts are small fibrous objects that are formed when protein and other materials settle in the kidney tubules and collecting ducts. Casts are dislodged by normal urine flow. A large number of them in a urine specimen is a sign of kidney disease.

Crystals

There are several different chemicals in body fluids that can form crystals that appear in urine. Some of these appear in normal urine, such as calcium oxalate or uric acid crystals. A large number of calcium oxalate crystals, however, may be a sign of abnormally high levels of calcium in the blood (hypercalcemia ). Other crystals, including tyrosine, leucine, and cholesterol, are abnormal. The presence of cystine crystals is a symptom of excessive urinary secretion of cystine (cystinuria ). Cystine is an acid found in many proteins and normally reabsorbed by the kidney tubules.

Protein

Protein in the urine can be a symptom of kidney stones, inflammation of the kidneys, degenerative kidney disease, or multiple tumors.

Sugars

A high level of glucose and other sugars in the urine (glycosuria) is often a symptom of diabetes mellitus. Glycosuria can also be caused by advanced kidney disease, Cushing's syndrome, impaired tubular reabsorption, shock, a rare tumor of the adrenal gland (pheochromocytoma ), or cancer of the pancreas.

Milk in the urine is normal if a woman is pregnant, has just given birth, or is breastfeeding. On the other hand, rare hereditary metabolic disorders are indicated when urine contains fruit sugar (fructose), milk sugar (galactose), or a simple sugar called pentose.

Ketones

The presence of abnormally high numbers of ketones in the urine (ketonuria) usually results from uncontrolled diabetes mellitus. Ketonuria can also be caused by prolonged diarrhea or vomiting that results in starvation.

KEY TERMS

Acidosis— A condition of the blood in which bicarbonate levels are below normal.

Alkalosis— A condition of the blood and other body fluids in which bicarbonate levels are higher than normal.

Casts— Small fibrous objects formed from materials that collect in the kidney tubules and are washed out by normal urine flow.

Catheter— A thin flexible tube inserted through the urethra into the bladder to allow urine to flow out.

Clean catch specimen— A urine specimen that is collected from the middle of the urine stream after the first part of the flow has been voided.

Colony count— A measurement of the growth of bacteria in a urine sample that has been cultured for 24 to 48 hours.

Fanconi's syndrome— A rare disorder caused by vitamin D deficiency or exposure to heavy metals.

Ketones— Substances produced during the breakdown of fatty acids. They are produced in excessive amounts in diabetes and certain other abnormal conditions.

Nephrotic syndrome— A condition characterized by water retention, little or no protein in urine, and high blood cholesterol.

pH— A chemical symbol used to describe the acidity or alkalinity of a fluid, ranging from 0 (more acid) to 14 (more alkaline).

Urethra— The duct that carries urine from the bladder to the outside of the body.

Urinalysis (plural, urinalyses)— The diagnostic testing of a urine sample.

Voiding— Another word for emptying the bladder or urinating.

Bilirubin

Bilirubin is an orange-yellow pigment found in bile, a fluid secreted by the liver. When it is found in urine, bilirubin may be a symptom of liver disease caused by the formation of fibrous tissue, medications that damage the liver, or obstructive jaundice.

Urobilinogen

Bacteria in the small intestine can convert bilirubin to urobilinogen, which is excreted in the feces, in bile, or in urine. An accumulation of urobilinogen in the urine may be a sign of severe infection, liver damage, or diseases that destroy red blood cells. Low levels of urobilinogen in the urine may be a result of antimicrobial therapy, inflammatory diseases, kidney disease, severe diarrhea, or blocked bile ducts.

Other findings

The presence of bacteria, parasites, or yeast cells in the urine may be a symptom of urinary tract infection or contamination of the external genitalia. Other factors that may affect urinalysis results include failure to collect a specimen during the day's first voiding; frequent urination; large dietary intake of vitamin C; and urine with a pH value lower than 6.

Resources

ORGANIZATIONS

American Association of Kidney Patients. 100 S. Ashley Dr., #280, Tampa, FL 33602. (800) 749-2257. 〈http://www.aakp.org〉.

American Kidney Fund (AKF). Suite 1010, 6110 Executive Boulevard, Rockville, MD 20852. (800) 638-8299. 〈http://216.248.130.102/Default.htm〉.

urinalysis , clinical examination of urine for the purpose of medical diagnosis. Urine is initially examined for such characteristics as color, odor, and specific gravity. It is routinely tested for acidity, as indicated by its p H reading, and screened for sugar, ketone bodies, proteins, and bile content. Benedict's solution, for example, may be used to test for simple sugars, a high level of which is a possible indicator of diabetes mellitus. Ketone bodies, e.g., acetone and acetoacetic acid, in the urine indicate the substitution of fats for sugar in the energy cycle and are another indication of diabetes mellitus. Abnormal levels of protein may be signs of kidney disease. A high concentration of bile in the urine is a sign of liver malfunction or blockage of the bile duct. Urine is examined microscopically to determine blood count. High levels of erythrocytes, or red blood cells, and leukocytes, or white blood cells, may be a result of bleeding and infection, respectively, in the urinary tract. Casts, crystals, and other substances, whose origins may be ascertained by determining their chemical structures, can be observed microscopically. Additional studies are performed when specific malfunctions are suspected. Clearance tests, for instance, will determine the ability of the kidneys to remove waste substances from the blood plasma per unit of time. The urine of patients with melanotic cancer will often contain melanin, a skin pigment. A diagnosis of drug addiction may be confirmed by the presence of specific chemical substances in the urine. Urinalysis is also employed to test for pregnancy. Pregnant women secrete high levels of gonadotrophic, or ovary-regulating, hormones from the placenta. A reagent containing gonadotrophic hormones is mixed with a sample of urine from the patient, and gonadotrophic antigens are added to it. Failure of the antigens to clump, or agglutinate, is positive evidence of pregnancy.

URINALYSIS

Urinalysis is an important test used in diagnosing diseases of the genitourinary tract. Urine is examined for pH and specific gravity by chemical and direct microscopic methods. The presence and concentration of various chemicals such as proteins, ketones, bilirubin, glucose, and nitrite are measured. Chemical metabolites also may be screened through urinalysis. In urinalysis, microscopic examination is performed to quantify the cellular urinary components, including red and white blood cells, fungi, and bacteria. The presence and concentration of cellular components, combined with the results of chemical analyses, give important clues for diagnosis of genitourinary diseases.

Bijan Shekarriz

Marshall L. Stoller

(see also: Genitourinary Disease; Urine Cytology; Urine Dipstick )

urinalysis (yoor-in-al-i-sis) n. the analysis of urine, using physical, chemical and microscopical tests, to determine the proportions of its normal constituents and to detect alcohol, drugs, sugar, or other abnormal constituents.