What if the t4 is drawn in a purple top tube?

purple top tube isn't the norm for T4 test but it may not hurt the results. This tube contains EDTA which is a chemical that hinder clotting. However, it still may dilute the specimen by a few microliters and should be considered by the phlebotomist.

red top tube should be used for extra accuracy, however, blood result within any human being can be changed that micro.. within seconds from another specimen that is drawn. All calibrations on machines almost never form the same results even on the same specimen.