Low iron anemia is why I get ferritin tests from my Hematologist. I also take iron supplement RX. I get constipated with the standard iron supplement, so my RX is for iron bisglycinate, which works for my iron level and is kind to my GI system.
I have had low iron anemia for over 10 years, so I forget what tests showed low iron anemia (I suspect it was low WBC and RBC ((CMP)) or low Hemoglobin and Hematocrit ((CBC))). However, I do remember all my doctors thinking I had a blood leak in my GI system. I had an upper GI Endoscopy, a colonoscopy, and a video capsule test, which inspected my GI system completely. No leaks were found, so I started with annual iron infusions in 2014 for 3 years until my iron/ferritin level was normal. The iron supplement RX has kept my ferritin level normal since 2019.
The anemia started in 2009 after my CABG then morphed into low iron anemia after 5 years