I'm not a huge fan of Dr. Mercola, due to his practice of selling supplements and other weird products on his website, but his video on IBS is pretty good. He covers the basics of the difference between IBS and IBD, looking for bacteria and adding probiotics. He doesn't however suggest screening to rule out Celiac disease first before attempting a gluten-free diet.
I believe screening for gluten intolerance or gluten sensitivity first is very important in terms of living a life-long gluten-free lifestyle. Remember, once you remove gluten from your diet for a period of time the antibodies used for testing are significantly reduced. Therefore someone who requests Celiac screening would test inconclusive. Living without a positive diagnosis of gluten intolerance or sensitivity can be tough when it comes to being tempted by favorite glutenous foods. The question of "just a little bit of gluten can't hurt me", or defending the GF diet to gluten consuming family members can cause unforeseen conflict. Gluten intolerance is genetic and runs along family lines and even though you suspect aunt M is gluten intolerant and suggesting she go on the diet too may be fighting words.
I also believe you should be screened for "non-celiac gluten sensitivity" just to make sure gluten is not being caused by an immune mediated response. You can do that by going to
(I am not affiliated in anyway with Dr. Fine or his lab)
So if you want to take a look at Dr Mercola's video on IBS here's the link: