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NBME 21 Answers

nbme21/Block 3/Question#47 (24.1 difficulty score)
A 48-year-old man comes to the physician ...
Increased intestinal iron absorption🔍

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submitted by chillqd(28),
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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. +10  
mangotango  Just to clear up definitions: Total Iron Binding Capacity (TIBC) = measure of trasnferrin molecules in the blood (bound by Fe or not). % Saturation = percentage of transferrin molecules that are bound by Fe (normally 33%) // Pathoma pg. 42 +  

submitted by chandlerbas(86),

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

submitted by dr.xx(130),
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adyerretih omat.ceohroshims

FEH is tdeautm tg;&= eth ieststneni perlaeltuyp rterentip a grtons srntarrefni aigsln as if teh ybdo wree iiefntecd ni oin.r iTsh lesda to mmlaiax onri atonsirbop ofrm eenidstg fdoos nda rnoi leaovrod in het sues.sti


lovebug  Autosomal recessive. C282Y mutation > H63D mutation on HFE gene, located on chromosome 6;associated with HLA-A3 [FA2019, PG.389] +