Is it true that a ferritin above 200 essentially rules out iron deficiency?

No, I do not think that a ferritin >200 ug/L essentially "rules out" iron deficiency. Ferritin is an acute phase reactant and can be elevated in myriad conditions including kidney disease, autoimmune disorders, etc. The transferrin saturation (measure of serum iron/TIBC) is an important marker of iron absorption in the gut and biologically available iron and should also be considered. In states of high inflammation, one would expect elevated levels of hepcidin to "trap" iron in the gut enterocyt...