@Delph: it also depends on what to test. Sometimes in order to have something tested, we also need to have something else tested otherwise the result does not mean anything and therefore need to see a doctor.
Wow, really? The lab I use for stuff never seems to ask, but it is a meat factory and all about the cash...
@User: if what you need to have tested is "rare", better to see an doctor. If you need to have more things tested, the doctor shall give you a complete prescription and you won't have to have several blood tests but only one.
What kind of blood tests would be so strange that a doctor would never agree to it? :/