Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1436 page)

   
Positive results:
Isolation of a common uropathogen at concentrations >10
⁴
colonies/mL (>10
³
colonies/mL for high-risk patients), when present as the sole or predominant isolate, is considered positive.

   
Negative results:
Urine culture is sensitive for ruling out UTI, but prior antimicrobial therapy can inhibit the growth of uropathogens, resulting in false-negative cultures.

   Limitations

   
Common pitfalls:

   Contamination, due to poorly collected or transported urine samples, limits the value of a significant proportion of specimens submitted to the laboratory.

   Clinically significant polymicrobial UTI is uncommon (<5%). Interpret mixed cultures with caution—they most likely indicate contaminated specimens.

   Urine is frequently transported in collection cups on which the caps are not firmly tightened, resulting in leakage and possible contamination.

   Urethritis and vaginitis may be associated with pyuria and clinically mimic cystitis.

Suggested Reading

McCarter YS, Burd EM, Hall GS, et al.
Cumitech 2C, Laboratory Diagnosis of Urinary Tract Infections
. Washington, DC: ASM Press, 2009.

VAGINITIS PANEL, MOLECULAR PROBE

   Definition and Use

   Symptoms of vaginitis and vaginosis are seen frequently in clinical practice. The most common causes are bacterial vaginosis (BV), trichomoniasis, and vulvovaginal candidiasis. Because of significant clinical overlap in the symptoms, specific diagnostic testing may be required to guide appropriate antimicrobial therapy and patient management.

   This test is based on pathogen detection by nucleic acid probe hybridization. The testing includes probes for the detection
Gardnerella vaginalis
(a marker for the disruption of the normal vaginal flora seen in BV),
Candida
species (for candidiasis), and
Trichomonas vaginalis
(for trichomoniasis).

   The assessment of test accuracy depends on the populations studied, the comparator method, and other factors.