Total Iron Binding Capacity

[applicant2002]

I am confused as to what exactly TIBC refers to. I thought I learned that TIBC is the amount of iron that could be bound to transferrin but is not, i.e. empty seats on a bus. Thus, for example, in Iron Deficiency Anemia, TIBC would be elevated because there is less iron to bind to the transferrin, and in hemachromatosis, there is too much iron that there are few empty seats left, so TIBC decreases.

However, now I am being told that TIBC is a measure of transferrin, not a measure of unsaturated transferrin. So the impression that I am getting is that transferrin increases in iron deficiency anemia because the body is trying to catch any iron that may be available, and it decreases in hematochromatosis because of reversal of the equilibrium.

Is the second paragraph accurate, or do I still not understand TIBC?
Thanks for all your help.

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[PACtoDOC]

I really wouldn't worry about it. From the first paragraph you wrote I can tell you have a fundamental understanding of TIBC. It basically is exactly as you stated in that it is high in low Iron states due to there being plenty of "empty seats". Just make sure you know which conditions alter TIBC. Anemia of chronic disease is the outlier that confuses people because TIBC can actually be normal or low I think, which is sort of counterintuitive. I am sure some medicine resident or IM wannabe will straighten this all out, but in the end, it sounds like you know it plenty well for boards.

 

[ckent]

I have always found this topic to be confusing too, so I decided to look it up. TIBC (Total Iron Binding Capacity) generally refers the amount of transferrin in the blood. It's measured by seeing how much iron can bind to proteins in the blood, and the protein being measured is transferrin. So that included the saturated and unsaturated transferrin. The amount of iron that could be bound to transferrin is called the unsaturated iron binding capacity. This I just read, I had never heard of that term being used in the hospital. In general, I believe that your conception of TIBC or transferrin is correct. Besides hematochromatosis, chronic diseases that supress liver protein output will also decrease TIBC. I'm not certain if the hematochromatosis works by reversing that equilibrium or if it works by suppressing the liver protein output. Anyways, hope that I was of some assistance. I'm still not 100% clear on this stuff either, that's just what I gathered from 5 minutes of reading. In general, for hospital floor purposes, I generally equate transferrin level with TIBC in the blood, and just know that TIBC and iron levels can be very misleading when trying to evaluate anemia. We were taught to mainly go by the ferritin levels (except in ESRD patients, which is a whole other story).

 

[Idiopathic]

Also remember the cases where the person has an anemia, but TIBC is low can also be due to anemia of chronic disease (serum ferritin will be increased). i.e. RA patient with anemia is probably not iron deficient (unless he/she takes aspirin chronically and has developed a GI bleed).

 

[applicant2002]

Thank you all for your quick responses. Thank you also for your reassurance. It's good to know that I am not the only one with the question. (I no longer feel that I have some big gaping hole in my schema of evaluating iron status in patients).