What could explain discordant iron studies?

This is an incredibly common question, largely generated by the zeal to use the serum ferritin and failure to appreciate the need for an overnight fast when ordering the TSAT (the ferritin does not require fasting). The most common culprit in this situation is iron containing vitamins. Prenatal vitamins or multivitamins for women contain enough iron to speciously raise the serum iron which in turn elevates the TSAT (Fe/TIBC). There is virtually nothing which will cause a low serum ferritin (abso...