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NBME 21 Answers

nbme21/Block 3/Question#47

A 48-year-old man comes to the physician because of ...

Increased intestinal iron absorption

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submitted by chillqd(11),

The Stem is describing hemochromatosis, characterized by abnormal iron sensing and increased intestinal absorption. This increases Iron, increasing ferritin. In response, TIBC is decreased, which increases transferrin saturation as there is less circulating carrier molecules.

With excess iron in the blood, it will accumulate in tissues including the liver, skin, pancreas. Sequelae include dilated cardiomyopathy, hypogonadism, diabetes, arthropathy 2/2 calcium pyrophosphate deposition, nd Hepatocellular Carcinoma

hello  I think you made one slight mistake. TIBC = total iron binding capacity. It is synonymous with "transferrin saturation". This patient has increased transferrin saturation aka increased TIBC. The transferrin molecules are saturated -- it is incorrect to say "as transferrin saturation increases, there is less circulating carrier molecules." It is more correct to say that the amount of free (unbound) transferrin is decreased. +1  
hpsbwz  @hello Transferrin saturation and TIBC are not synonymous. Transferrin is calculated using total body iron / TIBC. While the serum iron level continues to increase, the transferrin level decreases. Thus, the amount of transferrin available to bind iron (TIBC) decreases and the amount of transferrin saturated with iron (i.e., percent transferrin saturation) increases. +2  

theres so much iron in the blood that it has to go somewhere. it goes into the cells in the body (increased ferritin) and it binds to the carrier transport protein transferrin. because it binds to all the transferrin you have low free transferrin. but your body senses the low free transferrin and goes "ok all my transferrin are full of iron I guess im ok i dont need anymore iron" so it stops making transferrin. so low transferrin or total iron binding capacity (remember this is just a fancy way of saying it doesnt want transferrin).... now %transferrin sat is just math (i hate math) its like this: iron/TIBC, we already got high iron so numerator is high, and low denominator bc like i said TIBC is low so overall your %transferrin saturation is very high. this is the best indicator for hemochromatosis

 +1  upvote downvote
submitted by dr.xx(77),

hereditary hemochromatosis.

HFE is mutated => the intestines perpetually interpret a strong transferrin signal as if the body were deficient in iron. This leads to maximal iron absorption from ingested foods and iron overload in the tissues.