non-invasive...
My first visit, entailed going over my almost entire life history as it related to 'allergies'. You talk about why you are there for a bit, then are scheduled for a 'prick test' at a later date.
The test is relatively painless, they dip and prick mapped out places on an arm or other part of you wait 'x' minutes then wipe the allergens off. Measure the welts that result from the things you are allergic to, probably get a prescriptin for the more logical and treatable issues and off you go.

In my case, I got 'pricked' and we are talking really tiny needles dipped in possible allergy stuffs...about 40+ pricks and I survived, I received two meds for spring/fall allergies dominant in my region and off I go! I see the doc once a year for updates and new scripts.
Since I've other issues, and regularly get other types of blood tests. I bring copies of them to the office and usually walk out with them. Best to be safe than sorry tho.

Hope this eases your fears? - j

PS I can think of LOTS of docs that are much less fun to 'visit'!