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.

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