True about the sensitive assay. I've read alot on this site that says there isn't much of a difference when the number isn't really low. Is that correct? I was never taking vit D. Actually I don't take any supplements currently except fish oil. Have Jarrow Formulas Methyl B-12, 60 Lozenges 5000mcg on the way along with Now MSM powder to help with joint pain. Looking forward to starting the HCG.