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Photodynamic diagnosis (PDD) is a technique that enhances the detection of tumors during cystoscopy using a
photosensitizer which accumulates primarily in cancerous cells and will fluoresce when illuminated by violetblue
light. A disadvantage of PDD is the relatively low specificity. In this retrospective study we aimed to
identify predictors for false positive findings in PDD. Factors such as gender, age, recent transurethral resection
of bladder tumors (TURBT), previous intravesical therapy (IVT) and urinary tract infections (UTIs) were
examined for association with the false positive rates in a multivariate analysis. Data of 366 procedures and 200
patients were collected. Patients were instilled with 5-aminolevulinic acid (5-ALA) intravesically and 1253
biopsies were taken from tumors and suspicious lesions. Female gender and TURBT are independent predictors
of false positives in PDD. However, previous intravesical therapy with Bacille Calmette-Guérin is also an
important predictor of false positives. The false positive rate decreases during the first 9-12 weeks after the latest
TURBT and the latest intravesical chemotherapy. Although shortly after IVT and TURBT false positives
increase, PDD improves the diagnostic sensitivity and results in more adequate treatment strategies in a
significant number of patients.
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