It's a nice treat when a test involves absolutely no pain or fear, and this is one of those tests. But the Lactose Tolerance Test is balanced out by the fact that it's a huge inconvenience. Expect to be sitting in the waiting room for around 3 hours- bring a book, or an mp3 player. Or both.
You start off by having to eat a special diet 24 hours before the test. Your doctor should provide you with an information sheet about what you can and can't eat. You also can't eat or drink ANYTHING from 12 hours prior to the test. Stick to this carefully or you may be told you can't do the test. Expect to get thirsty. When you arrive you'll be asked to do an initial blow-test. You take a deep breath and blow into a plastic tube which inflates a plastic bag. The lab technician draws a sample of your breath out of the bag via a kind of syringe thing. That's it. Easy as pie.
You then wait while they test to see if your 'levels' whatever that means are low enough for you to take the test. No sense testing you I suppose if you were eating dairy the day before. I was fine so they brought me a glass of some lemon flavoured water stuff. Doesn't taste bad and it's easy to drink. I just don't like lemon so that was a bummer but no big deal. I assume this liquid contains lactose to test you with.
You then wait around the waiting room for 3 hours (!) doing the blow-test every half hour. Expect to have some little burps while waiting around. My hunger and thirst was also growing so that was annoying. But after the 3 hours and your final blow-test you're out of there. Simple, just very inconvenient- especially if the waiting room has uncomfortable chairs.
For myself, I'm not sure what is accomplished by having me take this test. Maybe my Doctor was just curious, because if it comes back positive then I'll have to avoid dairy- but I've already been doing that for years. If it comes back negative, then in theory milk is ok... but I already know SOMETHING in dairy bothers my stomach and I can't have it. So either way I still have to avoid dairy. For me... the test results won't really tell me much. It'll be odd if I do turn out to be lactose intolerant because for the first 20 years of my life I drank almost nothing but milk and ate tons of cheese with no problems. Can you develop lactose intolerance later in life? Can it be related to Crohn's? Questions to ask the doc.