I want to post this here for you to see I know sometimes things get lost in the shuffle. It's a previous post on another thread.
Ferritinlevels are a good way to detect IDA in the early stages because it's one of the first things to go. Having a low hemoglobin shows that the IDA is in a later stage. By the time your hemoglobin gets low it's time for iron, but why Dr's wait for that to happen is beyond me!
That is why I believe Dr's should use a ferritin test more often then not because it's a very early indicator of a problem before waiting for the last stages which are hemoglobin and hematocrit dropping. Ferritin takes months and years to raise and your body is putting the iron where it needs to be. Once your iron serum goes up it's going to start dumping back into your stores.