It is not necessary to have stool on the stool test swab, the swab is just a tool for the process of collecting stool, if the swab is kept directly, then the swab needs to have stool on it.
Stool examination is also known as routine fecal examination (fecal routine), to do routine fecal examination is not required to take feces in the anus, the first discharge of feces, and then use the swab to take a peanut-sized fresh feces into the specimen box, the specimen box should not be left for too long, 2 hours or less to send to the Laboratory Department for examination, left for too long is likely to affect the results of the test.
So the swab is used to take the feces tool, do not need to stay in the swab stool. However, there are also direct preservation of swabs, directly sent to the test, at this time the swab is required to have stool.