S0456 Revisiting the Cut-Off for an Abnormal Balloon Expulsion Test: Can We Make Testing More User Friendly?

Abstract

INTRODUCTION: Chronic constipation (CC) is a common gastrointestinal complaint in clinical practice. Anorectal Manometry (ARM), Balloon Expulsion Testing (BET), and Defecography (DEF) are used to evaluate for dyssynergic defecation (DD) in CC patients. Literature provides poor to moderate agreement between ARM, BET, and DEF. The current threshold for a normal BET is <60 seconds. This threshold, though widely adopted, has not been rigorously validated. Our aim was to determine if a shorter or longer expulsion time offers improved performance characteristics to the current cut off for an abnormal BET of <60-seconds. METHODS: A retrospective cross-sectional study was conducted on 4746 CC patients ≥18 years of age who were referred for AFT at a single tertiary-care center from July 2003 to February 2020. All CC patients underwent an ARM and BET with a sub-set completing an ARM, BET, and DEF (n = 726). Abnormal AFT were defined as the following: ARM = simulated defecation responses with ≤20% anal relaxation; BET = the inability to expel a 50 ml water-filled balloon in ≤60-seconds; DEF = paradoxical contraction, increase anorectal angle, and/or the inability to expel barium contrast. DD was defined as an abnormal ARM and DEF. Linear BET time marks were coded for an abnormal test every 30-seconds: 30–120 seconds. Sensitivity, specificity, positive predictive values (PPV), and negative predictive values (NPV) were calculated for each 30-second BET time point using an abnormal ARM, DEF, and DD as individual state variables. RESULTS: Demographics (N = 4746) were as follows: mean age 48.8 ± 16.4 years (18–93), mean BMI 27.5 ± 7.2, 81.8% female, and 85.3% Caucasian. The BET sensitivity and specificity were similar at 30, 60, 90, and 120 seconds for an abnormal ARM, DEF, and DD (Table 1). The PPV for identifying an abnormal ARM for BET using a threshold of 120 seconds (sec) = 79%, for BET 90 sec = 68.0%, BET 60 sec = 62.1%, and BET 30 sec = 47.7% (Table 1). The NPV for BET 120 sec = 27.9%, BET 90 sec = 44.6%, BET 60 sec = 50.9%, and BET 30 sec = 62.7% (Table 1). Similar profiles for PPV and NPV for abnormal DEF and DD relative to various BET time thresholds (Table 1). CONCLUSION: A BET threshold of <60 seconds offers the best combination of performance characteristics for dyssynergic defecation relative to a few different gold standards and should remain the standard for defining an abnormal BET.Table 1