I agree 100%. But even with a blood test you need to be careful! I was taking 1000iu (doctors orders after a blood test) for about a month and it made my calcium spike above the normal range. I have freaky genes when it comes to Vitamin D and should have been taking more Vitamin K7 with it. But I now get it all from seafood, mostly salmon, since salmon also contains calcitonin [1].

[1] Evidence that calcitonin stimulates 1,25-dihydroxyvitamin D production and intestinal absorption of calcium in vivo.

https://pmc.ncbi.nlm.nih.gov/articles/PMC423580/