You can't eat in the morning when you apply for a health certificate, because the main purpose of the health certificate is to check whether the liver function is normal and whether there are infectious diseases. So be sure to have an empty stomach before the examination, and don't drink water.
And colds can also affect the examination of liver function. If you really have a cold, do you want to check it? It's better to wait until it's ready, which is more accurate.