Problems in Assessing Screening Experience in Observational Studies of Screening Efficacy: Example of Urinalysis Screening for Bladder Cancer

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Abstract
Objective: – To evaluate screening urinalysis for its efficacy in preventing fatal bladder cancer. Methods: –A case-control study of 290 case subjects with fatal bladder cancer v 290 age and sex matched control subjects, with ascertainment of urinalyses by medical record review. Results: –In the five years before the symptoms that led to the detection of bladder cancer, case subjects had significantly fewer routine (screening) urinalyses than controls (matched odds ratio for one or more urinalyses v none = 0.60 [95% confidence interval (CI) 0.41 to 0.87], adjusted for cigarette smoking and occupational bladder cancer risk). However urinalyses for urinary symptoms and problems before those that led to bladder cancer diagnosis were more frequent in the cases; hence there was only a small statistically non-significant deficit in cases of urinalyses for all reasons combined (corresponding adjusted odds ratio 0.94, 95% CI 0.61 to 1.46). Since urinalyses for symptoms and problems could have led to the detection of bladder cancer, the latter finding appears more applicable. Methodological problems included: difficulty in assigning the reason for urinalysis; the possibility that clinically indicated urinalyses led to a reduction in screening urinalyses; and difficulty in identifying the detectable and curable preclinical phase for targeting ascertainment of urinalyses. Reducing potential efficacy, haematuria on urinalysis, particularly transient or mild asymptomatic microhaematuria, was often not followed up by cystoscopy. Conclusions: –This study did not show that ordinary urinalysis was effective in preventing fatal bladder cancer but because of methodological problems a clear answer may require a randomised controlled trial.