A plain abdominal X-ray, which showed free air, was used
in the diagnosis of PUP in the hospital setting during the study
period. A previous study used fast ultrasound or computerized
tomography scan to confirm diagnosis and early treatment of
PUP as plain abdominal X-ray does not always prove perforation,
particularly in the early stages.14,15 Several case series
have shown that in 30%–50% of patients, the X-ray may be
negative for free air, particularly in the elderly.15 Unfortunately,
ultrasound and computed tomography scans are limited in a
developing country such as Thailand. Therefore, most cases in
this study could not be confirmed by using this equipment