Urinalysis (Urine Test)

Picture of urine dipstick and color box instructions; photo courtesy of iStock

A urinalysis is simply an analysis of the urine. It is a very common test that can be performed in many healthcare settings, including doctors' offices, urgent care facilities, laboratories, hospitals, and even at home.

A urinalysis test collects a urine sample from the patient in a specimen cup. Usually, only small amounts (30-60 mL) may be required for urinalysis testing. The sample can be analyzed in the medical clinic or sent to a laboratory to perform the tests. Urinalysis is abbreviated UA.

UA is in general easily available and relatively inexpensive. It is also a simple test and can provide many useful information about various diseases and conditions. Some physicians refer to urinalysis as "a poor man's kidney biopsy" because of the plethora of information that can be obtained about the health of the kidney or other internal diseases by this simple test.

Urine can be evaluated by its physical appearance (color, cloudiness, odor, clarity), also referred to as a macroscopic analysis. It can be also analyzed based on its chemical and molecular properties, including microscopic assessment.

Urinalysis is ordered by doctors for several reasons, including the following:

• Routine medical evaluation: general yearly screening, assessment before surgery (preoperative assessment), admission to hospital, screening for kidney disease, diabetes mellitus, hypertension (high blood pressure), liver disease, etc.
• Assessing particular symptoms: abdominal pain, painful urination, flank pain, fever, blood in the urine (hematuria), or other urinary symptoms.
• Diagnosing medical conditions: urinary tract infections, kidney stones, uncontrolled diabetes (high blood sugars), kidney impairment, muscle breakdown (rhabdomyolysis), protein in urine (proteinuria), drug screening, and kidney inflammation (glomerulonephritis).
• Monitoring disease progression and response to therapy: diabetes-related kidney disease, kidney impairment, lupus-related kidney disease, blood pressure-related kidney disease, kidney infection, proteinuria, and hematuria
• Pregnancy testing

Macroscopic urinalysis is the direct visual observation of the urine, noting its quantity, color, clarity, or cloudiness, etc.

Normal urine is typically light yellow and clear without any cloudiness. Obvious abnormalities in the color, clarity, and cloudiness may suggest the possibility of

• An infection (cloudy urine)
• Dehydration (dark urine color)
• Liver disease ("bilirubin," a digestive substance secreted by the liver, stains urine a tea or cola color)
• Blood in the urine (hematuria -- visible may indicate urinary tract infection, stones, tumors, or injuries)
• Breakdown of muscle (orange- or tea-colored urine)

Certain medications may also change the color of urine (for example, phenazopyridine, a urinary antiseptic and pain reliever). Very foamy urine may represent large amounts of protein in the urine (proteinuria).

The microscopic urinalysis is the study of the urine sample under a microscope. It requires only a relatively inexpensive light microscope. Cells and cellular debris, bacteria, and crystals in the urine (crystalluria) can be detected by microscopic examination to confirm the dipstick color change (see above) and further clinical clues.

Urinalysis can disclose evidence of diseases, even some that have not caused significant signs or symptoms. Therefore, a urinalysis is commonly a part of routine health screening.

Urinalysis is commonly used to diagnose a urinary tract or kidney infection, to evaluate causes of kidney failure, and to screen for the progression of some chronic conditions such as diabetes mellitus and high blood pressure (hypertension).

It also may be used in combination with other tests to diagnose some diseases. Additional tests and clinical assessments are often required to further investigate the findings of urinalysis and ultimately diagnose the causes or specific features of underlying problems. For example, urine infection is generally diagnosed based on the results of urinalysis. However, urine culture is often ordered as a follow-up test to confirm the diagnosis and to identify the bacteria that may be causing the infection. Other examples include kidney stones, inflammation of the kidneys (glomerulonephritis), or muscle breakdown (rhabdomyolysis).

Interpretation of urinalysis is generally based on reviewing all the components of the test and correlating it with the clinical signs and symptoms of the patient and the physical examination. The results are reviewed and interpreted by the doctor who ordered the test.

Many types of doctors may order a urinalysis in their practice. Because of easy availability, relatively nominal cost, simplicity of performing the test, and quick turnaround time, UA is done in many settings by a variety of doctors. Most frequently, UA is ordered by internists, family practitioners, emergency-room physicians, obstetricians and gynecologists, nephrologists (kidney specialists), urologists, rheumatologists, and possibly less often by many other specialists.

Urinalysis is done by collecting a urine sample from a patient. The optimal sample tends to be an early morning urine sample because it is frequently the most concentrated urine produced in the day. Typically, no fasting is required before the collection of urine samples and routine medications can be taken before the test unless otherwise instructed by the ordering physician.

Methods of collection are slightly different for female and male patients.

• For females, the patient is asked to clean the area around the urethra with a special cleansing wipe, by spreading the labia of the external genitals and cleaning from front to back (toward the anus). The cleaning hand is then used to maintain the spread while the cup is held by the other hand to collect the sample.
• For men, the tip of the penis may be wiped with a cleansing pad before collection.
• The urine is then collected in a clean urine specimen cup while the patient is urinating. It is best to avoid collecting the initial stream of urine. After the initial part of the urine is disposed of in the toilet, then the urine is collected in the urine container provided. Once about 30 mL to 60 mL (roughly 3 to 5 tablespoons) are collected in the container for testing, the remainder of the urine may be voided in the toilet again. This is called the midstream clean catch urine collection.

The collected urine sample should be taken to the laboratory for analysis, typically within one hour of collection. If transportation to the lab could take more than one hour, then the sample may be refrigerated.

In some patients who are unable to void spontaneously or those who are not able to follow instructions, other methods may be used, such as placing a catheter (a small rubber tube) through the outside opening to the bladder (urethra) to collect the sample directly from the bladder.

The urine test strip is a narrow plastic strip that has several squares of different colors attached to it. Each small square represents a component of the test used to interpret urinalysis. The entire test strip is dipped in the urine sample and color changes in each square are noted. The color change takes place after several seconds to a few minutes from dipping the strip. If read too early or too long after the urinalysis strip is dipped, the results may not be accurate.

Each color change on a particular square may indicate specific abnormalities in the urine sample caused by a certain chemical reaction. The reference for color changes is posted on the plastic bottle container of the urine test strips. This makes for an easy and quick interpretation of the urinalysis results by placing the strip next to the container and comparing its color changes to the reference provided.

The squares on the dipstick represent the following components in the urine:

• Specific gravity (concentration of urine)
• The acidity of the urine (pH levels)
• Protein in the urine (proteinuria), mainly albumin
• Glucose (sugar) in the urine (glycosuria)
• Ketones in the urine (ketonuria), products of fat metabolism
• Hemoglobin/blood in the urine (hematuria)
• Leukocyte esterase (suggestive of white blood cells in urine)
• Nitrite (suggestive of bacteria in urine)
• Bilirubin (possible liver disease or red blood cell breakdown)
• Urobilinogen (possible liver disease or etodolac [Lodine] medication)

The presence or absence of each of these color changes on the strip provides important information for clinical decisions.

After the dipstick test strip is dipped in urine briefly and completely, the reading is done within a few minutes. Each one of the squares on the box has next to it the time that is recommended for its interpretation (for example, whether there is a change in color on the square). The squares are placed in similar order on the box, from the ones requiring the shortest time to read of 30 seconds to the ones with the longest time to read of two minutes. This arrangement is based on result time and makes it easier to quickly read and interpret any color changes by simply scanning the strip from the shortest (glucose) to the longest (leukocytes).

Microscopic urinalysis is done by simply pouring the urine sample into a test tube and centrifuging it (spinning it down in a machine) for a few minutes. The top liquid part (the supernatant) is discarded. The solid part left in the bottom of the test tube (the urine sediment) is mixed with the remaining drop of urine in the test tube and one drop is analyzed under a microscope.

The sediment is examined through the microscope under low power to identify what are called casts, crystals, squamous (flat) cells, and other large objects.

The examination is then performed through the microscope at higher power to further identify any cells, bacteria, and clumps of cells or debris called casts.

The main advantage of a urine test strip is that they are convenient, easy to interpret, and cost-effective. They can be analyzed within minutes of urine collection in the doctor's office or in the emergency room to provide valuable information.

However, what can be learned from a dipstick is limited by the design of the dipstick. The main disadvantage is that the information may not be very accurate, as the test is time-sensitive. It also provides limited information about the urine, as it is a qualitative test and not a quantitative test (for example, it does not give a precise measure of the quantity of abnormality). Therefore, normal and abnormal values are not reported as part of urinalysis results.

Epithelial cells (flat cells), and red and white blood cells may be seen in the urine.

Sometimes cells, cellular debris, and casts are seen in the microscopic exam. Epithelial cells (cells in the lining of the bladder or urethra) may suggest inflammation within the bladder, but they also may originate from the skin and could be contaminated.

Casts and cellular debris originate from higher up in the urinary tract, such as in the kidneys. These are materials shed from the kidney cell lining due to injury or inflammation and travel down through the urinary tubes. These usually suggest an injury to the kidney from an inflammation or lack of blood flow to the kidneys. Rarely, tumor cells can be in the urine suggesting a urinary tract cancer.

Red blood cells can enter the urine from the vagina in menstruation or from the trauma of bladder catheterization.

A high count of red blood cells in the urine can indicate infection, trauma, tumors, or kidney stones. If red blood cells seen under microscopy look distorted, they suggest the kidney as the possible source and may arise due to kidney inflammation (glomerulonephritis). Small amounts of red blood cells in the urine are sometimes seen in young healthy people and usually are not indicative of any disease.

Urine is generally thought of as a sterile body fluid, therefore, evidence of white blood cells or bacteria in the urine is considered abnormal and may suggest a urinary tract infection such as bladder infection (cystitis), or infection of the kidney (pyelonephritis). White blood cells (WBC) may be detected in the urine through a microscopic examination (pyuria or leukocytes in the blood). They can be seen under a high power field and the number of cells is recorded (quantitative) as "rare, few, moderate, or many."

White cells from the vagina or the opening of the urethra (in males, too) can contaminate a urine sample. Such contamination aside, the presence of abnormal numbers of white blood cells in the urine is significant.

Other commonly performed urine tests are drug tests, pregnancy tests, and specific chemicals and proteins in the body, which are not a part of routine urinalysis.

Urine drug screen is done routinely to check for drugs or their byproducts in the urine. There are many purposes for these tests including athletic screening, emergency room settings, drug detoxification programs, and school and employment screening.

This test detects the presence of commonly used drugs such as:

• Cocaine
• Amphetamines
• Methamphetamines
• Marijuana
• Phencyclidine
• Barbiturates
• Benzodiazepines
• Opiates

The urine pregnancy test is very common and it measures a hormone in the urine associated with pregnancy (beta-HCG or beta-human chorionic gonadotropin). This test can be done in medical settings, but numerous kits are available for home use.

Other urine tests can also be used in the evaluation of many medical conditions. Examples include

• Urine culture (in determining the bacterial cause of urine infection)
• Urine creatinine (in assessing kidney disease)
• Urine total protein and albumin (in assessing kidney disease and protein loss from the kidney)
• Urine cytology (in evaluating for possible bladder or other urinary tumors)
• Urine calcium (in evaluating elevated blood calcium levels)
• 24-hour urine collection for proteins (in diagnosing causes of kidney impairment, diabetic-related kidney disease, lupus-related kidney disease)
• 24-hour urine collection for protein electrophoresis (for measuring different components of proteins in urine in evaluating multiple myeloma, and kidney inflammation with increased protein loss)
• 24-hour urine collection of catecholamine metabolites (in evaluating adrenal gland disease, difficult to treat high blood pressure)