Validation of New Type Radiopaque Marker in The Evaluation of Colonic Transit Time

The goal of this clinical trial is to learn if the local made colonic transit capsule can be use to diagnose slow transit constipation. The main questions it aims to answer are: * Does the local made colonic transit capsule correlate with the standard colonic capsule in the diagnosis of slow transit constipation? * Does the number of remained radiopaque marker similar between the two test after five days of ingestion? Researchers will compare the local made colonic capsule with the standard Sitzmark colonic capsule to see the correlation. Participants will: * Take both local made colonic capsule and Sitzmark colonic capsule at the same time. * Obtain abdominal x-ray 5 days after capsule ingestion. * Keep a diary of their symptoms and medication used during investigation.

The accurate diagnosis of constipation subtype is crucial especially in patients refractory to treatment. The current methods are expensive and not widely available. Thus, the investigators design the clinical study to evaluate the correlation and diagnostic accuracy of local made colonic transit capsule (Siriraj gastrointestinal transit capsule) compare with standard colonic capsule. The patients with constipation and healthy volunteers will be enrolled. Participants will be asked to take both Sitzmark colonic capsule and Siriraj gastrointestinal transit capsule. The two capsules have different shape of radiopaque marker. The abdominal x-ray will be taken 5 days later. The number of radiopaque marker left will be counted separately between the two type of markers. Slow transit constipation is defined with retained more than 20% of radiopaque marker at 5 days after ingestion. Primary outcome is the correlation in the diagnosis of slow transit constipation and number of remained radiopaque markers between Sitzmark colonic capsule and Siriraj gastrointestinal transit capsule and the secondary outcome is the diagnostic performance of Siriraj gastrointestinal transit capsule in detecting slow transit constipation with Sitzmark colonic capsule as standard reference.