Serum ferritin, introduced in 1972, became the primary measure of iron status, shifting focus from circulating iron to stored iron.

“and we can thank Jacobs at all 1972 British medical journal for introducing us to serum Fittin it's a very important Pro Storage protein because up until that time everyone knew that hemoglobin was how you measured iron status because it was the circulating iron not the stored iron everything flipped in 1972 and all the Optics went to storage and let's forget about the circulating which is that was a tragedy of biblical proportions”