Alteration of maximum anal resting pressure by digital rectal examination prior to manometry: analysis of agreement between repeat measurements.

To study whether digital examination preceding anal manometry causes significant alteration of maximum resting pressure reading and to quantify the discrepancies, 78 individuals (64 incontinent, 14 controls) were investigated. Recordings of maximum resting pressure were taken before and after digital rectal examination. There was a mean discrepancy of only -1.8 cms H2O between the readings and excellent correlation, but analysis of agreement revealed a bias that tended to be greater with smaller measurements and unacceptable variability between test results. Furthermore, the bias was not related to age, gender, the grade of incontinence, maximum voluntary contraction, functional anal canal length and threshold volume. Digital rectal examination prior to manometry causes unpredictable results especially in patients with lower maximum resting pressures and should strictly be avoided.