by Cat Troiano
Urination is one of the body’s ways of eliminating metabolic waste, which is why a urinalysis is an important diagnostic screening method. For something that is considered waste, one to two ounces of that waste can provide a wealth of information regarding the body’s metabolic efficiency. Is it enough to make a definitive diagnosis, or is it a valuable noninvasive first step?
Who Should Be Tested?
When the body expels urine, it is eliminating excess water and sodium. Perspiration and, to a much lesser extent, exhalation also rid the body of water. Urine, however, also rids the body of creatinine, uric acid, urea and other toxic compounds that the kidneys filter from the bloodstream. Other compounds can also be shed in the urine, and their presences serve as indicators of illness.
A urinalysis should be ordered along with a routine comprehensive metabolic blood panel and complete blood cell count to provide a complete metabolic health evaluation. Urinalyses are also performed to aid in diagnosing the following conditions:
• Urinary tract infections
• Chronic kidney disease
• Liver disease
If a patient has any of these conditions, periodic urinalyses are ordered to monitor the illness so that changes in treatment protocols can be implemented as needed.
Urinalyses should be ordered at once when a patient presents with signs of urinary illness. Such signs include:
• persistent urge to urinate
• passing only minimal amounts of urine
• pain or burning sensation during urination
• blood seen in the urine
• pains in the back, side or abdomen
If a urinary tract infection is suspected, a urine culture should also be ordered.
While pregnancy can be diagnosed from a urine sample, the telltale hormone is not included in a urinalysis and must be detected in a separate test, which is the human chorionic gonadotropic urine test. However, routine urinalyses are ordered as part of an expectant mother’s prenatal examinations to screen for such conditions as gestational diabetes.
A urinalysis is also part of a pre-op screening to confirm that the kidneys are functioning optimally to process anesthetic agents and to alert physicians to the presence of diabetes or infection, which will need to be addressed prior to any surgical procedures.
Urinalysis: A Three-Step Process
A complete urinalysis is performed in three steps, which include a physical analysis, a chemical analysis and a microscopic analysis.
Urine should be straw to pale yellow in color, and it should be clear, not cloudy. It should not have a particularly foul odor. Medications and foods can affect these physical aspects of urine. For example, have some beets for dinner tonight, and then see what color your urine appears when you visit the bathroom tomorrow. Rhubarb, blackberries and carrots can also alter the color of urine, asparagus can change the odor, and a high protein diet can make the urine appear cloudy. Even the extent to which a patient is hydrated can be evidenced in their urine’s appearance. Sneak a peek at your urine the next time you visit the bathroom. If your urine looks clear or a pale shade of yellow, then your body is properly hydrated. If your urine is bright yellow or darker in color, then you are not drinking enough water.
Ironically, some drugs that are used to treat urinary tract infections, such as phenazopyridine, can tint urine into an orange hue. Other medications that can alter any urinalysis results include, but are not restricted to:
• Certain antibiotics, such as metronidazole, rifampin and nitrofurantoin
• Sulfasalazine, a drug used to manage ulcerative colitis, rheumatoid arthritis and Crohn’s disease
• Propofol, an anesthetic agent
• Promethazine, a drug used to control asthma
• Certain vitamins and minerals, such as vitamin C and riboflavin
• Cimetidine, an antihistamine
• Levodopa, a drug used in the treatment of Parkinson’s disease
• Laxative preparations that contain senna
• Amitriptyline, an antidepressant
• Anticoagulant drugs
• Methocarbamol, a muscle relaxant
• Potassium citrate, which is used to treat kidney stones as well as gout
• Thiazide diuretics, which are antihypertensive drugs
• Sodium bicarbonate drugs used to treat acid indigestion
After a visual inspection for color and clarity, two laboratory screenings are performed to complete the urinalysis.
Acidity is represented as a pH level. Neutral pH has a value of 7. The normal pH reference range is 5.0 to 8.0. A result that is higher than this range, interpreted as an alkaline, or basic, level may be caused by urinary tract infection, urinary tract obstruction and renal failure, and can also result if a patient has been vomiting. A high pH level can also occur in patients with respiratory alkalosis. When the urine pH value is lower than the normal range, interpreted as an acidic level, this may be the result of diabetic ketoacidosis, dehydration, starvation and acidosis, and can also result if a patient is having diarrhea.
Bilirubin is a resulting by-product from the normal breakdown of red blood cells. It is normally passed along to the liver, where it is allocated into bile. Bilirubin should not be present in urine. If bilirubin is detected on a urinalysis, additional tests to evaluate liver function should be pursued.
Urobilinogen is a by-product of bilirubin. Urobilinogen is primarily excreted through defecation, but small amounts may be passed through urination. The normal reference range for urobilinogen is 0.2 to 1.0 mg/dL. If the test results exceed that range, then additional tests to evaluate liver function should be pursued.
Blood in the urine, known as hematuria, is not normal. Blood that is detected on a urinalysis can be indicative of kidney or bladder infection, kidney or bladder stones, renal cancer, bladder cancer or a blood disorder. Further tests will be necessary to achieve a specific diagnosis. Menstruation should be ruled out first in female patients.
Specific gravity reveals how efficiently the kidneys are able to concentrate the urine. The normal specific gravity reference range is 1.003 to 1.035. Results lower than the reference range are indicative of kidney disease. Results higher than the reference range can be a result of dehydration.
Glucose should not be detectable when performing a urinalysis. If the result is not negative, then further testing should be ordered to confirm a diagnosis of diabetes.
Ketones are the byproduct of the breakdown of fat and should not show up on a urinalysis. If the result is not negative, then further testing should be ordered to confirm a diagnosis of diabetes. Extreme low-carbohydrate diets can also lead to ketones in the urine.
Protein in the urine, or proteinuria, should be investigated further if the result exceeds a normal reference range of 0 to 20 mg/dL. Higher results can result from kidney disease, urinary tract or bladder infection, diabetes and dehydration, as well as hypertension or health conditions caused by eclampsia in pregnant women.
Nitrites are nitrogen compounds that can result when Gram-negative bacteria, including E. coli, release an enzyme that converts nitrates into nitrites. When nitrites are detected on a urinalysis, a urinary tract infection is the likely explanation.
Leukocyte esterase is produced by leukocytes, one of the five types of white blood cells in the body. As in the case of nitrites, if leukocyte esterase is detected on a urinalysis, a urinary tract infection should be suspected.
If any abnormalities are detected, the microscopic analysis will help to confirm the initial findings.
• Leukocytes, or white blood cells
• Erythrocytes, or red blood cells
• Bacteria, which is a strong indicator of infection
• Casts, which are microscopic particles that can be made up of fat, protein or blood cells
• Crystals, the presence of which indicate bladder or kidney stones
Once the urinalysis is complete, the combined results provide more pieces of the diagnostic puzzle.
Putting the Tests Together
As informative as a urine specimen is, a urinalysis must be combined with additional tests to definitively rule out and confirm the causes of abnormal results. This is why a complete metabolic profile should accompany a urinalysis, as the metabolic profile will reveal specific values of renal and liver function as well as blood glucose levels. If crystals are seen on the microscopic analysis, additional tests and/or procedures should be performed to ascertain the size and number of stones as well as to determine if they are calcium oxalate, uric acid or struvite stones. In the case of a urinary tract infection, a urine culture will identify the offending bacteria and guide in the selection of the most effective antibiotic to combat the infection. If diabetes is suspected, further tests must be ordered so that an effective treatment plan for the patient’s disease management can be formulated.