Some modern examination procedures can be used to check for possible problems even where there are sometimes no apparent symptoms. For example, this can be the case with some frequently occuring types of cancer when symptoms are sometimes not yet apparent. But such diseases can turn out to be life threatening.
Common examples are:
For smokers, a simple CT scan can identify early lung cancer, which, if treated early, can often be successfully cured.
For women over the age of 40, mammography is usually the examination of choice for the prevention/early detection of breast cancer.