Have you ever been tested for Vitamin D deficiency ?

I have never been checked for Vit D deficiency. The thing is, in northern tier states, almost EVERYONE is Vit D deficient during the winter. Summer, it depends on how much you get out into the UV.... yup. Sunshine helps convert Vit D into a useable form. Yes, you can take Vit D supplements, increase your food intake with Vit D fortification....but you still need some sunshine to help it become USEABLE.

I thought it would be something that's tested every time I had my blood drawn. Apparently, not.

No, not sure what that would be for? Brittle bones?