Discounting the duration of bolus exposure in impedance testing underestimates acid reflux.
BACKGROUND
Combined impedance-pH testing (MII) allows for detection of reflux episodes regardless of pH. However impedance-based diagnosis of reflux may not routinely account for duration of the reflux episode. We hypothesize that impedance testing may be less sensitive than pH-testing in detecting acid reflux off therapy as a result of discounting duration of exposure.


METHODS
Baseline characteristics and reflux parameters of MII studies performed off-anti-secretory medications were analyzed. Studies on acid suppressive medication and those with recording times less than 20 h or low baseline impedance were excluded.


RESULTS
A total of 73 consecutive MII studies were analyzed of which 31 MII studies had elevated acid exposure while 16 were abnormal by impedance criteria. MII testing off-therapy was more likely to be abnormal by pH criteria (percent time pH < 4) than impedance criteria (total reflux):[42 vs 22 % (p =0.02)]. Acid exposure (percent time pH < 4) identified more studies as abnormal than MII-detected acid reflux episodes [42 vs 34 % (p < 0.01)]. Mean acid clearance time (pH-detected) was significantly longer than median bolus clearance time (impedance-detected) in the total [98.7 s vs 12.6 s (p < 0.01)], upright [58.6 s vs 13.1 s (p < 0.01)], and recumbent positions [136.7 s vs 14.2 s (p < 0.01)] with the greatest difference seen in the recumbent position. The mean ratio of mean acid clearance time (pH-detected) and the median bolus clearance time (impedance-detected) was significantly higher in the recumbent position compared to the upright position [11. vs 5.3 (p = 0.01)].


CONCLUSIONS
Ambulatory impedance testing underestimates acid reflux compared to esophageal acid exposure by discounting the prolonged period of mucosal contact with each acid reflux episode, particularly in the recumbent position.
Department of Gastroenterology and Hepatology, Singapore General Hospital, Singapore, Singapore.
Namasivayam
N
Vikneswaran
Division of Gastroenterology and Hepatology, Department of Immunology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA. murray.joseph@mayo.edu.
Joseph A
JA
Murray
D000328:Adult; D000368:Aged; D017097:Electric Impedance; D050782:Esophageal pH Monitoring; D005260:Female; D005764:Gastroesophageal Reflux / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011187:Posture; D012189:Retrospective Studies; D013997:Time Factors
Impedance; Reflux