Youtube "fungal biofilm intestine" or something like that. Take a look at the videos , its like having plastic bags inside your small intestine , it covers the intestines skin and stops it absorbing b vitamins. So you get malabsorption issues. There are many ways to test , if you mean a simple blood test where you do no work and its effortless, then no. But if you want to put in the work, you can easily test it and find out yourself, for example drinking mct c8 oil and seeing if you suddenly get very ill and need to also use the loo a lot, i.e die off herx reaction happens from the caprilyc acid , so you have fungus in your intestine. If nothing happens then you dont. Dont get caught up on what type of fungus. Anyway theres loads of tests you can do , you can try fluconazole, itraconazole , terbinafine each on their own for a week at a time and see what happens. Is there again, any die off herx reaction to any of those anti fungals. Check out the /candida sub on reddit and formulate your own plan of action though. Im not a doctor or a functional heath doctor and dont recommend doing anything I mentioned without doing your own research first. Whatever you do, you will see fungal biofilm and a lot of it in your stool , if you successfully get a die off of the fungus.