When should I not use the screening kit?

In order to take a sample at least 5 days must have passed since your last period ended. There are a few other requirements: no antibiotics or antifungals in the last 30 days, no douching, penetrative vaginal sex, and vaginally applied meds or creams in the 24 hours before. That will ensure your microbiome is in a stable state and that your results are not inconclusive.