Loosely related to the topic of testing in general … Feb 2014 article: "This Woman Invented a Way To Run 30 Lab Tests On Only One Drop of Blood" http://www.wired.com/2014/02/elizabeth-holmes-theranos/
Her company, Theranos, has partnered with many Walgreens Wellness Centers (search for one near you at their website) and offers a price menu (https://www.theranos.com/test-menu?ref=our_solution
), which includes some nutrient testing at very reasonable prices – ferritin, magnesium, vitamin B12, vitamin D 25-OH. I assume that a doctor's order is still necessary for most tests, although I have not confirmed this – some tests may be available on a walk-in basis, as I know there are labs which do tests on a walk-in basis.
And still more loosely related… In a TV news report recently, I heard about SaveOnMedical (https://www.saveonmedical.com/
) which helps patients compare and find affordable medical procedures. At present, it is set up for radiology procedures. The "Find Labs" feature is still to come – I don't know if this will include phlebotomy and lab tests.
As for vitamin D (25-hydroxy D) testing specifically, GrassrootsHealth is offering their test through March 31 for $48.75 (plus $5 shipping) – once you receive the test kit, it requires pricking a finger to obtain a few drops of blood which are put on supplied blotter card and returned by mail. This does NOT require a doctor's order. http://www.grassrootshealth.net/march-2 ... cial-offer