Urinalysis Proves Simple, Safe and Inexpensive

Edition: May 2002 - Vol 10 Number 05
Article#: 1246
Author: Repertoire

The value of analyzing urine for signs of disease has been accepted for many centuries – as early as 400 B.C., says Mary Lou Gantzer, PhD, manager, clinical and outcomes research for the diabetes and urine chemistry product lines at Bayer Corp, Business Group Diagnostics, Elkhart, IN. Since then, urinalysis technology has come a long way, from the original, vague visual screenings, to the liquid alkaline copper sulfate test for urine sugar developed in the early 1900s, to the tablet test in the 1940s, to the more modern dip-and-read tests. Today, urinalysis is one of the most common lab tests of all, used to monitor diabetes or kidney disease, or to detect a urinary tract infection.

The test calls for the physician or technician to dip a commercially treated strip – or ''dipstick'' – into a sample of urine (about two tablespoons). The strip changes color when dipped into the urine, indicating whether kidney problems exist. An excessive amount of protein, or proteinura, in the urine is a sign that the kidneys are malfunctioning, according to William F. Keane, M.D., president of the National Kidney Foundation (NFK).

An example of the latest dip-and-read technology is Bayer Corp.'s (Tarrytown, NY) Multistix Pro Reagent Strip, which measures the urinary concentration of protein with a sensitivity of 8-15 mg/dL, as well as the level of creatinine. The Multistix Pro Reagent is reportedly the one dipstick test that estimates the protein-creatinine ratio, notes Bayer.

Whereas healthy kidneys retain only what is needed and filter out wastes and excess fluids, failing kidneys are unable to retain protein, which then appears in the urine. If a urinalysis reflects the presence of protein in the urine, the patient should undergo further testing to explore the possibility of kidney disease. As is usually the case with testing and diagnosis, early detection means earlier treatment and a greater chance that the disease can be arrested. At the first sign of kidney disease, the right diet and various medications can help slow down the process of kidney failure.

The NFK stresses that physicians perform a routine urinalysis for the following high-risk populations:
• Patients with high blood pressure.
• Senior citizens.
• Patients with a family history of kidney disease.
• African Americans, Hispanics, Asian Americans, and American Indians.

Testing enables physicians and patients to be aware of a number of potential urinary tract and kidney problems early on, including:
• Red blood cells, an indication of chronic kidney disease.
• Kidney stones, bladder cancer or a blood cell disorder such as sickle cell disease.
• Glucose, a sign of diabetes.
• Bacteria and white blood cells, a sign of infection or vaginal or bladder disease.
• Elevated acid levels.

Preparing for Urinalysis
A urinalysis is risk-free and pain-free, and calls for little preparation. The patient must clean the area around the urethra to prevent contaminating the urine sample. Also, the sample should be collected in mid-stream to ensure it is clean. Other collection methods include:
• Early morning collection of a urine sample prior to ingesting fluid.
• Catheterization (i.e. in cases where the patient is comatose or confused).
• Suprapubic transabdominal needle aspiration of the bladder. The collection method ideally can provide the purest urine sample, and is recommended for infants or toddlers.

For the most accurate results, the technician should perform a urine test within 15 minutes after the urine is collected. The more time that elapses after a sample is collected, the greater the risk is of one or more of the following changes occurring:
• Decreased clarity from crystallization of solutes.
• Increased pH.
• Loss of Ketone bodies.
• Loss of bilirubin.
• Dissolution of cells and casts.
• Spread of contaminating microorganisms.

The urine sample is analyzed both macroscopically and microscopically. Macroscopic analysis – or direct visual observation – focuses on the physical characteristics of the urine, such as specific gravity, color and clarity.

Lab technicians determine specific gravity (urine density or the ability of the kidney to dilute the urine over that of plasma) using a total solids meter or a chemical method on a dip-and-read strip. Measures of specific gravity alone are of limited value, according to Gantzer. But, knowing whether urine is diluted or concentrated impacts the way the technician will interpret other urine tests.

Similarly, urine color must be analyzed relative to the complete urinalysis. Most samples (95 percent to 99 percent) are yellow in color. The remaining samples will vary depending on medications or food pigments ingested. Usually, fresh urine is clear; cloudy urine suggests the presence of white blood cells, epithelial cells, or bacteria; and smoky turbid urine suggests the presence of red blood cells, according to Gantzer.

Using the dip-and-read or dipstick chemical analysis, the technician can look at the following:
• pH. A pH of 7.4 to about 6 is common, although urinary pH can range from 4.5 to 8.0.
• Specific gravity. A reading between 1.002 and 1.035 on a random sample is considered normal if the kidneys are working normally. Urine with a specific gravity over 1.035 either is contaminated or has very high levels of glucose, or the patient has recently received high-density radiopaque dyes intravenously for radiographic analysis.
• Protein. Normal total protein excretion should not exceed 150 mg/24 hours or 10 mg/100 ml in any single specimen. Samples with excessive levels of protein are classified as proteinuria, a condition that can be severe. Dipsticks usually detect protein by producing a color with an indicator dye, Bromphenol blue.
• Glucose. Less than 0.1 percent of glucose normally filtered by the glomerulus appears in the urine. An excess of sugar in the urine indicates diabetes mellitus.
• Ketones. Acetone, aceotacetic acid, and beta-hydroxybutyric acid resulting from diabetic ketosis or fasting are detected via the dipstick.
• Nitrite. A positive nitrite test suggests a significant presence of bacteria.
• Leukocyte Esterase. A positive leukocyte esterase test signifies the presence of white blood cells.

(Source: The Internet Pathology Laboratory for Medical Education, Florida State University College of Medicine.)

Microscopic Urinalysis
During the microscopic examination of urine, a 10-15 ml sample of well-mixed urine is centrifuged in a test tube at a relatively low speed of 2 rpm to 3000 rpm. This process lasts from five to 10 minutes until a somewhat cohesive button forms at the bottom of the tube. The tube is decanted, leaving a volume of 0.2 ml to 0.5 ml inside. The sediment is resuspended by flicking the bottom of the tube, and a drop of resuspended sediment is poured onto a glass slide for examination.

The technician first examines the slide under low power to identify most crystals, casts, squamous cells and other large objects. Later, the technician switches to high power to identify crystals, cells and bacteria.

The following cells may be detected microscopically in urine samples:
• Red blood cells. Hematuria, or the presence of too many red blood cells in the urine, may be caused by glomerular damage, tumors that have eroded along the length of the urinary tract, kidney trauma, urinary tract stones, renal infarcts, acute tubular necrosis, upper and lower urinary tract infections, nephrotoxins, and physical stress. Sometimes red blood cells can migrate into the urine of healthy persons. But, if one or more red blood cells are discovered microscopically in every high power field and contamination is unlikely, the urine specimen probably is abnormal.
• White blood cells. Pyuria, or the presence of too many leukocytes or white blood cells, is a sign of infection in the upper or lower urinary tract. If two or more leukocytes per each high-power field show up in noncontaminated urine, the sample most likely is abnormal.
• Epithelial cells. These include renal tubular, transitional and squamous epithelial cells. Increased numbers of renal tubular epithelial cells point to nephritic syndrome or conditions leading to tubular degeneration. The presence of squamous epithelial cells suggests that the urine specimen may be contaminated with skin flora.

(Source: The Internet Pathology Laboratory for Medical Education, Florida State University College of Medicine.)

Confirming Test Results
Because pharmaceuticals, food or disease can interfere with urinalysis test results, physicians often request confirmations of original positive results. While the physician on one hand has his or her ideas about which tests should be confirmed, this remains subject to debate, according to Gantzer. It follows, however, that confirmatory tests should have better, if not the same, sensitivity and specificity as the original test.

Given how inexpensive and easy it is to complete a urinalysis – especially the macroscopic portion of the test – the argument for including a routine urinalysis in patient office visits is strong. Some research shows that over the last 10 to 15 years as much as 10 percent to 30 percent of urinary abnormalities have been discovered during routine health screening, according to Gantzer. True, not all abnormalities detected will call for intervention. But, the results might enable both the patient and physician to take an active role in shaping the patient's health.