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FAQs
Our facility screens for UTIs using urine dipsticks. Other facilities use urinalysis or leukocyte strips. Are there advantages to switching to CultureStat for screening purposes?
Yes. CultureStat determines the presence or non-presence of log phase (infectious) bacteria in a urine sample by measuring the respiration and increase in cell mass of viable and infectious bacteria in such sample. Dipsticks, urine strips and urinalysis do not detect or measure bacteria directly; each instead infers the presence of bacteria by detecting the presence of nitrites, leukocyte esterase or white blood cells in a urine sample. As the presence of nitrites, leukocyte esterase or white blood cells does not always correlate with the presence of a UTI, these rapid tests are inherently unreliable for the specific determination of whether or not a patient has a UTI.
Dipsticks and paper strips are used to detect presence of nitrites or leukocyte esterase (or both) in urine. If nitrites are present, it might mean some level of bacteria is present and converting normal nitrates in urine to nitrites. Leukocytes are white blood cells and are not normally present in urine. Leukocytes are detected indirectly using dipsticks or strips by detecting leukocyte esterase, an enzyme produced by such cells, or by urinalysis. In any case, these measures are entirely assumptive--they are not specific for viable infectious bacteria nor are they able to determine microbial concentration thresholds.
Both dipstick and paper strip tests are subject to variability due to sample volume, subjective reading of the dipstick's or strip’s color gradient, and improper sampling methods. Presence of either nitrites or leukocyte esterase does not necessarily mean there is an infection, clinically defined as 10e5 cfu/ml bacteria. Positive results on nitrites or leukocyte esterase can mean one of many conditions exists and requires further diagnosis; they do not always mean a UTI is present. The same is true for urinalysis, which determines the presence or non-presence of white blood cells, not the presence or non-presence of viable and infectious bacteria.
The limitations of dipsticks, urine strips and urinalysis for accurately determining whether or not a patient has a UTI are well documented in medical studies. A recent analysis of 75 papers analyzing whether negative dipstick urine analysis is sensitive enough to rule out UTI in adults with urinary symptoms concluded dipsticks to be of insufficient sensitivity to rule out UTI in patients with one or more symptoms.1,2 One such study concludes that dipstick analysis is not sufficiently sensitive for diagnosis of UTI in high-risk patients in whom missed diagnosis would have serious consequences.3 Another study concludes that nitrite and leukocyte esterase assays miss significant microscopic findings with corresponding clinical pathology.2,4 A negative dipstick result does not reliably rule out a UTI in clinical situations in which symptoms and signs of UTI are present.5 On the flip side, positive results of leukocyte esterase or nitrite tests do not necessarily indicate infection.6 Dipsticks and microscopic urinalysis are generally not considered to be adequate screening tools during pregnancy or for children.7,8 The uses of both dipsticks and urinalysis result in significant cases of false negatives (negative results from the dipstick or urinalysis when the urine culture was positive) and false positives (positive results from the dipstick or urinalysis when the urine culture was negative) to the extent that Lammers et al concluded that “the limitations in the diagnostic accuracy of both tests [dipsticks and urinalysis] should be incorporated into medical.”9
Because CultureStat rapidly measures for the presence or non-presence of actual log phase bacteria, and not nitrites or white blood cells, it produces results which are significantly higher for accuracy, sensitivity and specificity compared to the common rapid testing methods. And as results are available in 30 minutes for fresh samples, caregivers can use CultureStat to perform UTI screening with the speed necessary for rapid patient diagnoses and the accuracy associated with traditional culture methods.
References:
1 Ohly N, Teece S. Accuracy of negative dipstick urine analysis in ruling out urinary tract infections in adults. Emerg Med J 2003; 20 (4): 362-3.
2 Rehmani, R. Accuracy of urine dipstick to predict urinary tract infections in an emergency department. J Ayub Med Coll Abbottabad, 2004.
3 Eidelman, Y. Reagent strip diagnosis of UTI in a high-risk population. Am J Emerg Med 2002; 20: 112-3.
4 Propp DA, Weber D, Ciesla ML. Reliability of a urine dipstick in emergency department patients. Ann Emerg Med 1989; 18(5): 560-3.
5 Hurlbut TA, Littburg B. The diagnostic accuracy of rapid dipstick tests to predict urinary tract infections. Am J Clin Pathol 1991; 96: 582-6.
6 Abu Ghoush, MW. Screening test for detection of urinary tract infections: evaluation of the urinary leukocyte esterase dipstick test. TAF Prev Med Bull 2008; 7(3): 187-90.
7 Delzell J, Lefevre M. Urinary tract infection during pregnancy. Amer Famil Physc 2000: 1: 1-10.
8 Lohr JA. Use of routine urinalysis in making a presumptive diagnosis of urinary tract infection in children. Pediatr Infec Dis. 1991; 10:646-50.
9 Lammers RL, Gibson S, Kovacs D, Sears W, Strachan G. Comparison of test characteristics of urine dipstick and urinalysis at various test cutoff points. Ann Emerg Med 2001 Nov; 38(5): 505-12.
Does CultureStat identify the species of bacteria present in a sample?
No; CultureStat detects the presence or non presence of log phase bacteria, but does not identify the type of species in positive samples. Statistically, 85-89% of all samples tested for bacterial infection are negative. Presently hospital and independent laboratories spend significant time and resources testing this high percentage of negative samples. By using CultureStat as the first round screening methodology, negative samples can be accurately identified and confirmed much more quickly, and need not be plated. Negative results can be reported back to doctors within a few hours of sample collection, rather than 24-48 hours or longer. Positive results can go to a speciation plate for identification much more quickly with CultureStat compared to traditional first-round plating.
Our lab has been testing urines the same way for years, and I am concerned with incorporating CultureStat into the work flow of our lab. Will the introduction of CultureStat have a detrimental effect on work flow?
Not at all; because CultureStat is extremely efficient and simple to use, lab personnel can quickly and easily introduce the system into their work flow with minimal training required. Use of CultureStat will significantly reduce the staffing, time and space required for first-round urine culture testing.
How important is it to be able to distinguish between log phase bacteria and lag phase bacteria?
Extremely important! Urinary tract infections are caused by bacteria growing in log phase. If a testing methodology cannot distinguish between bacteria in log phase and bacteria not in log phase, it cannot determine whether such bacteria is actually causing an infection in the body. For more information, see Log vs Lag Phase. For a study by an independent laboratory on CultureStat's ability to distinguish between log phase growth and lag phase growth (and the inability of the plating methodology to distinguish between log phase and lag phase growth), see News or click here.
Can the results from CultureStat be downloaded to our hospital’s primary database system?
Yes. Results from the CultureStat reader are automatically stored on the database included in the CultureStat database program. The program allows for one-click downloading of results to the hospital’s primary database system, and real-time downloading of data to the hospital’s primary database system is available. Data can also be emailed, searched, sorted, printed and downloaded to Microsoft Excel and other popular software programs. Because the database uses bar code identification of samples, rather than a patient’s name or other recognizable identification information, hospitals can use the program in accordance with their HIPAA compliance programs.
If a sample is positive, can a speciation plate be streaked with urine contained within the CultureStat ampoule, or must the lab maintain the original sample for the purpose of speciation testing?
There is no need to maintain the original sample for speciation testing. If speciation testing is required for a sample, the urine can be used directly from the CultureStat ampoule and streaked onto a speciation plate for identification.
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