When is the best time to test for Beta-glucuronidase? Does it matter if I'm in the luteal or follicular phase of my cycle?

Beta-glucuronidase levels are primarily influenced by your gut microbiome, but because this enzyme also plays a role in estrogen metabolism, the phase of your cycle may have some effect. If you're testing to investigate estrogen-related symptoms, the luteal phase (about a week before your period) might give the most relevant picture. That said, testing can be done at any time of the cycle, especially if you're looking at overall gut health trends.