Urinalysis

Urinalysis is used as a screening and/or diagnostic tool because it can detect different metabolic and kidney disorders. Often, substances such as protein or glucose will begin to appear in the urine before patients are aware that they may have a problem. It is used to detect urinary tract infections (UTI) and other disorders of the urinary tract. In some conditions, urinalysis also provides an easy, economical, and relatively fast test to follow patient progress, for example, if you want to know whether a condition is getting better or worse. However, a urinalysis cannot detect all disorders.

A routine urinalysis may be done when you visit your doctor, when you attend the outpatient clinic or when you are admitted to the hospital. It may also be part of a routine medical examination, a new pregnancy evaluation, or preparation for planned surgery. A urinalysis will most likely be performed if you see your doctor complaining of tummy pain, back pain, painful or frequent urination, or blood in the urine. This test can also be useful in monitoring whether a condition is getting better or worse.

Urinalysis results can have many interpretations. Abnormal findings are a warning that something may be wrong and should be looked at further. Normal urinalysis results do not mean there is no illness. Urinalysis is only one screening test that can provide a general overview of a person’s health. Your doctor must look at the urinalysis results alongside your health complaints and other information available.

No prior preparation is needed for a spot urine test, unless specified by your doctor.

Urinalysis testing is frequently carried out by dip-stick testing in the clinic and results are available immediately. This is called near-patient testing or point of care testing (POCT). If there is an abnormal finding, such as excessive protein or the presence of blood, it may be necessary to send the sample on to the laboratory for further analysis. This will take several days and depending on the tests that need to be carried out.

During the visual examination of the urine, the healthcare professional may look at the urine’s colour, clarity, and concentration. Urine can be a variety of colours, most often shades of yellow, from very pale or colourless to very dark or amber.

Unusual or abnormal urine colours can be the result of a disease process, some drugs or foods. For example, some people produce red-coloured urine after eating beetroot. The colour is from the natural pigment of beetroot and is not a cause for worry. Red-coloured urine can also occur when blood is present in the urine, and can be an indicator of disease or damage to some part of the urinary system.

Blood can also be a contaminant that gets into the urine unintentionally during collection, such as from haemorrhoids or menstruation. Once this contaminating blood is in the urine, it will be detected during the chemical phase of a urinalysis, and your doctor will initially assume that it came from the urinary tract. The importance of blood in urine is discussed further in the chemical and microscopic examination sections.

The depth of urine colour is also a crude indicator of urine concentration:

• Pale yellow or colourless urine indicates dilute urine where lots of water is being excreted.
• Dark yellow urine indicates concentrated urine and the excretion of waste products in a smaller quantity of water, such as is seen with the first morning urine, with dehydration, and during a fever.

Urine clarity refers to how clear the urine is. Usually clarity of the urine is reported as: clear, slightly cloudy, cloudy, or turbid. “Normal” urine can be clear or cloudy. Substances that cause cloudiness but that are not considered unhealthy include mucus, sperm and prostatic fluid, cells from the skin, normal urine crystals, and contaminants such as body lotions and powders. Other substances that can make urine cloudy, like red blood cells, white blood cells, protein or bacteria, indicate a condition that requires attention.

Urine colour and clarity can be a sign of what substances may be present in urine. However, confirmation of suspected substances is obtained during the  chemical and microscopic examinations.

Chemical examination is usually done using test strips. These are narrow plastic strips that hold small squares of paper called test pads, arranged in a row. The test pads have chemicals impregnated into them. When a strip is briefly, but completely, dipped into urine, the test pads absorb the urine and a chemical reaction changes the colour of the pad within a few seconds or minutes.

The nurse, doctor or laboratory scientist compares the colour change for each reaction pad to a colour chart provided with the test strips to give a result for each test. Each reaction pad must be evaluated at the appropriate time for that chemical. If too little time or too much time has passed since the reaction, the laboratory scientist may get incorrect results. To reduce timing errors and eliminate variations in colour interpretation, sometimes automated instruments may be used to “read” the reaction colour of each test pad.

The degree of colour change on a test pad can also give an approximation of the amount of substance present. For example, a slight colour change in the test pad for protein may indicate a small amount of protein present in the urine whereas a deep colour change may indicate a large amount.

The most frequently performed chemical tests using reagent test strips are

• specific gravity,
• pH,
• protein,
• glucose,
• ketones,
• blood,
• leukocyte esterase,
• nitrite,
• bilirubin, and
• urobilinogen.

Some test strips also have a test pad for ascorbic acid (vitamin C).

New near patient testing devices (POCT) give a machine-readable result quantifying the concentration of some tests as mentioned above (e.g. glucose, specific gravity, bilirubin), and/or give positive or negative result.

The first test, specific gravity, is a measure of urine concentration and is measured using a chemical test.

There are no “abnormal” specific gravity values. This test simply indicates how concentrated the urine is. Specific gravity measurements provide a comparison of the amount of substances dissolved in urine as compared to pure water. If there were no solutes present, the SG of urine would be 1.000 – the same as pure water. Since all urine have some substances dissolved, a urine SG of 1.000 is not possible. If a person drinks excessive quantities of water in a short period of time or gets an intravenous (IV) infusion of large volumes of fluid, then the urine SG may be as low as 1.002. The upper limit of the test pad, an SG of 1.035, indicates a concentrated urine. 

pH is not generally a very helpful test. As with specific gravity, there are typical but not “abnormal” pH values. The kidneys play an important role in maintaining the acid-base balance of the body. Therefore, any condition that produces acids or bases in the body such as  acidosis or alkalosis, or the ingestion of acidic or basic foods, can directly affect urine pH.

Diet can modify urine pH. A high-protein diet or consuming cranberries will make the urine more acidic. A vegetarian diet, a low-carbohydrate diet, or the ingestion of citrus fruits will tend to make the urine more alkaline.

Some of the substances dissolved in urine can precipitate out to form crystals when the urine is acidic, others can form crystals when the urine is basic. If crystals form while the urine is being produced in the kidneys, a kidney stone or “calculus” can develop. By modifying urine pH through diet or medications, the formation of these crystals can be reduced or eliminated.

The pH can change and become less acidic if the urine is not tested within a few hours of collection. Therefore, samples to test pH should arrive the lab as soon as it is collected.

The protein test pad usually measures the amount of albumin in the urine. Testing albumin in urine is routinely performed in patients with diabetes mellitus. Normally there will not be detectable quantities of the protein albumin. When urine protein is levels are high, you have a condition called proteinuria; this can be an early sign of kidney disease. Albumin is smaller than most other proteins and is typically the first protein that is seen in the urine when kidney dysfunction begins to develop. Other proteins are not generally detected by the test pad but may be measured using a separate urine protein test. Other conditions that can produce proteinuria include

• Disorders that produce high amounts of proteins in the blood, such as multiple myeloma
• Infections of the urinary tract
• Conditions that destroy red blood cells
• Inflammation, malignancies (cancer), or injury of the urinary tract – for example, the bladder, prostate, or urethra
• the presence of blood in the urine perhaps due to stones which are damaging the walls of the kidney or bladder
• Vaginal secretions that get into and contaminate the urine

Glucose is not normally present in urine. When glucose is detectible, the condition is called glycosuria. It results from either

1. An excessively high glucose concentration in the blood, such as may be seen with people who have uncontrolled diabetes.
2. A reduction in the "kidney threshold".  When blood glucose levels reach a certain concentration then the kidneys begin to excrete glucose into the urine.  Sometimes the threshold concentration is reduced and glucose enters the urine sooner- at a lower blood glucose concentration.

Some other conditions that can cause glycosuria include hormonal disorders, liver disease, certain drugs, and pregnancy. When glycosuria occurs; other tests such as blood glucose are usually performed to further identify the specific cause.

A microscopic examination may or may not be performed as part of a routine urinalysis. It will typically be done when there are abnormal findings on the physical or chemical examination. It is performed on urine sediment – urine that has been centrifuged to concentrate the substances in it at the bottom of a tube. The fluid at the top of the tube is then discarded and the drops of fluid remaining are examined under a microscope. Cells, crystals, and other substances are counted and reported either as the number observed "per low power field" (LPF) or "per high power field" (HPF). In addition, some entities, if present, are estimated as "few," "moderate," or "many," such as epithelial cells, bacteria, and crystals.

Normally, a few RBCs are present in urine sediment. Inflammation, injury, or disease in the kidneys or elsewhere in the urinary tract, for example in the bladder or urethra, can cause RBCs to leak out of the blood vessels into the urine. RBCs can also be a contaminant due to an improper sample collection and blood from haemorrhoids or menstruation.

The number of WBCs in urine sediment is normally low. When the number is high, it indicates an infection or inflammation somewhere in the urinary tract. WBCs can also be a contaminant, such as those from vaginal secretions.

Normally in men and women, a few epithelial cells from the bladder (transitional epithelial cells) or from the external urethra (squamous epithelial cells) can be found in the urine sediment. Cells from the kidney (kidney cells) are less common. In urinary tract conditions such as infections, inflammation, and malignancies, more epithelial cells are present. Determining the kinds of cells present helps the doctor pinpoint where the condition is located. For example, a bladder infection may result in large numbers of transitional epithelial cells in urine sediment. Epithelial cells are usually reported as “few,” “moderate,” or “many” present per low power field (LPF).

In health, the urinary tract is sterile: there will be no microorganisms seen in the urine sediment. Microorganisms are usually reported as “none,” “few,” “moderate,” or “many” present per high power field (HPF). Bacteria from the surrounding skin can enter the urinary tract at the urethra and move up to the bladder, causing a urinary tract infection (UTI). If the infection is not treated, it can eventually move to the kidneys and cause pyelonephritis. Less frequently, bacteria from a blood infection (septicaemia) may move into the urinary tract. This also results in a UTI. Special care must be taken during specimen collection, particularly in women, to prevent bacteria that normally live on the skin or in vaginal secretions from contaminating the urine. A urine culture may be performed if a UTI is suspected.

In women (and rarely in men), yeast can also be present in urine. They are most often present in women who have a vaginal yeast infection, because the urine has been contaminated with vaginal secretions during collection. If yeast are observed in urine, then tests for a yeast (fungal) infection may be performed on vaginal secretions.

Trichomonads
Trichomonads are parasites that may be found in the urine of women or men (rarely). As with yeast, the trichomonads are infecting the vaginal canal and their presence is due to contamination. If these are found during a urinalysis, then follow-up testing for Trichomonas vaginalis may be performed to look for a vaginal infection.