Sick leave or not?

I have a hospital appointment tomorrow (nothing major, don't worry). Officially in my workplace, we're supposed to take doctor's appointments in our own time rather than registering them as sick leave. Whilst this doesn't seem unreasonable for when I'm able to make an appointment outside of office hours, it seems wrong to me for when I'm given a hospital appointment in the middle of the day.

What do you think? What does your workplace rule? And do you abide by it? [Reply anonymously if you prefer.]