Is urinalysis cost-efficient or timely?
Every year more than 300 million routine urinalyses are performed in the US alone. The cost to the patient usually starts at $25 to $35 but might increase an additional $100 to $300 by the time a culture and sensitivity are run.
Urinalyses are often shipped cross country to a clinical or reference laboratory. As a result, less than 70% of samples that show significant bacterial count are reported in 2 to 3 days or less, which is not ideal for the affected patient.
Lorincz and his associates are investigating a procedure to solve these problems. Using a technique known as supravital microscopic fluorescence technique (SMFT), they can screen a sample onsite in less than 5 minutes to determine whether a culture is needed. They can also determine whether the causative organism is a cocci, rod, spirochete, Mycoplasma, or even Legionella--though not the specific microorganism species.
In comparison to standard urine cultures, an abstract in the Annals of Clinical and Laboratory Sciences (May 1995) found that SMFT detected 92% of the samples with significant bacteriuria. Another preliminary study of 218 samples, published in 1999 in the July/ September issue of the Annals of Clinical and Laboratory Science, compared the SMFT method with traditional laboratory urinalysis and bacterial culture. SMFT had a positive test predictive value of 73%, a sensitivity of 83%, a predictive negative test value of 93%, and a specificity of 92%. A third, larger study of SMFT has been currently submitted to a peer-reviewed publication.
SMFT uses a small aliquot of uncentrifuged urine and an equivalent amount of fluorochrome solution (acridine orange in a sterile phosphate buffer solution) on a slide. Sealing the edges of the coverslip with paraffin and using the epi-fluorescence microscope at 40X or 100X objective, each cell and microorganism "lights up the night," remarked Lorincz. Comparing the technique to standard light microscopy, Lorincz states, "It's like looking at the moon at night compared to looking at it in daylight" (see Figure 1). By using a halogen source instead of a traditional mercury lamp, Lorincz holds the cost of the microscope he uses to less than $7,500.
Although Lorincz is quick to agree that more research is needed to establish the usefulness of SMFT for screening urinary tract infections, he points out such testing is expensive. And, he remarks "there aren't a lot of people who are interested in laboratory methodology procedures other than the people who run reference labs." In an effort to further SMFT technology, he published the formula for the buffered fluorochrome. Furthermore, Lorincz assured MLO that if anyone wants it for experimental purposes, he is willing to share it. He would love to see SMFT used routinely in place of urinalysis "to provide better and quicker service. In addition, it would be safer for patients because unnecessary medication would not be prescribed."
SMFT is one of several techniques attempting to improve on the "gold standard" for diagnosing a urinary tract infection--the traditional Gram stain followed by a bacterial culture. Although many laboratories now routinely use either dipstick testing to determine the presence of white blood cells in the urine or leukocyte esterase and nitrite as a presumptive indicator of a microbiological infection, this is not considered to be as reliable.
But, John Koepke, MD, professor emeritus at Duke University Medical Center in Durham, NC, notes, "People are latching onto the idea that the dipstick tested negative, and so we're not going to do the urine culture."
Whether a dipstick test alone is accurate enough in screening for bacteriuria is moot. One study by Semeniuk and Church published in the September 1999 issue of Journal of Clinical Microbiology found the dipstick test inadequate in 18.9% of the urine samples of 479 women. These samples were deemed negative based on the leukocyte esterase test and/or nitrite test, but a culture revealed significant bacteriuria.
Conversely, Waisman and associates found dipstick tests to be comparatively useful. In a small study published in 1999 in Pediatrics, they found the dipstick test had a sensitivity of 97.1% compared with urinalysis at 88.6% and the catalase test (Uriscreen) at 100%. The dipstick had a negative predictive value of 98.6% compared with urinalysis at 95% and the catalase test at 100%. The specificity of the dipstick was 82.5% versus 88.4% for urinalysis and 56.4% for the catalase test.
Lorincz estimates the cost savings of using SMFT at billions of dollars--money that would otherwise be spent on unneeded culture and sensitivity testing and unneeded antibiotics. Furthermore, "The SMFT is not all that complicated," says Lorincz. "Technically, not only can you do it in the doctor's office," the technique is so simple "you can teach an eighth grader how to do it."
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|Publication:||Medical Laboratory Observer|
|Article Type:||Brief Article|
|Date:||Nov 1, 2000|
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