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NBME 21 Answers

nbme21/Block 3/Question#31 (50.5 difficulty score)
A 28-year-old woman at 18 weeks' gestation ...
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 +66 
submitted by assoplasty(93),
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I itkhn eht onccept ’hteeyr sngitte si hte irdecensa GBT lvseel in cgepyna,nr nda otn tsuj sdhiremrhyitopy ni le.rnega

hWne ncneirges rfo yioy,e/rdhirhphotspmy STH selevl rae WLAYAS efatepnryllire eckedch esceabu they are reom nevsteiis ot etnuim fceirfensde in T/43T. ftOne tsmie THS ellsve cna aetsdtneorm a ceangh veen ehnw T3/4T sevlel aer in hte accubsnilil gane.r The only toxpcieen to sthi udlwo eb in ygacenpnr nda( I egssu yemba vlrie r?ialufe I utdob etyh oludw kas tish )h.ohtug igHh toergnes vleels vesnetpr eht lvier fmor garknbie owdn BT,G ledgina ot esrncdeai GBT svllee ni hte us.rme ihTs idsbn to feer 4,T nedrgiaces eht amunto of aabiveall rfee T4. As a paeotcsoynrm in,cmehmas SHT sveell are ttrnsaniyle needasric adn eth EART of 4T intuocpord si ceeisdrna ot shnreielp ebsinael eefr 4T leev.ls oweevrH eht LTAOT tmuoan of T4 is daice.enrs

Teh tsoniuqe si aknigs owh ot rnomcif midyesoyhhrirtp ni a taprngen wonma -&t-g; uoy deen to khcec FEER T4 lslvee bsuac(ee yteh uhdlos be loarmn due ot nrsmotyacpoe )nrs.eepso uYo ancnot ecchk THS u(slyula elveadte in npnyagrec ot noemtspeac for edaseicrn )TB,G and uyo tnacno ehkcc altto 4T svllee iwll( be ae)ridnsce. You got eth wernas tghri hteeri awy btu I nkith shti is a ffenrtedi agnnoesir trowh oiecr,nsngid ubaesec yeth cna aks tshi tcponce in ehtro teotncxs of gnmesrre,osiy-hpet dan fi yhet stiled S“”TH sa na ewrsan chioce htta luwod eb ecrcrtin.o

hungrybox  Extremely thorough answer holy shit thank u so much I hope you ACE Step 1 +8  
arkmoses  great answer assoplasty, I remember goljan talking about this in his endo lecture (dudes a flippin legend holy shit) but it kinda flew over my head! thanks for the break down! +2  
whoissaad  you mean total amount of T4 is "not changed"? 2nd para last sentence. +  
ratadecalle  @whoissaad, in a normal pregnancy total T4 is increased, but the free T4 will be normal and rest of T4 bound to TBG. If patient is hyperthyroid, total T4 would still be increased but the free T4 would now be increased as well. +1  
maxillarythirdmolar  To take it a step further, Goljan mentions that there are a myriad of things circulating in the body, often in a 1:2 ratio of free:bound, so in states like this you could acutally see disruption of this ratio as the body maintains its level of free hormone but further increases its level of bound hormone. Goljan also mentions that you'd see the opposite effect in the presence of steroids and nephrotic syndromes. So you could see decreased total T4 but normal free T4 because the bound amounts go down. +1  
lovebug  Amazing answer! THX +  
an_improved_me  Just to add: Pregnancy is not an exception to using TSH in suspected hyperthyroid pregnant patients (not sure in hypothyroid); you would still get a TSH first, and if its unusually low, you would then proceed to measure T4 (free, total), and so on. https://www.uptodate.com/contents/hyperthyroidism-during-pregnancy-clinical-manifestations-diagnosis-and-causes?search=hyperthyroidism%20in%20pregnancy&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2#H994499 +  



 -4 
submitted by cantaloupe5(77),
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dmtrheH/pyoishyrpoiy is asdigendo ihwt THS /w exlefr to T4 tihs( sujt tlles het bla fi TSH is mlaorn ’ondt kcehc 4T utb if HST si rabo,amln hcekc T4 o.)ot HTS nwst’a an tnpioo os 4T is eht setb n.easrw

hello  I don't get why this was downvoted... +2  
maxillarythirdmolar  To take it a step further, Goljan mentions that there are a myriad of things circulating in the body, often in a 1:2 ratio of free:bound, so in states like this you could acutally see disruption of this ratio as the body maintains its level of free hormone but further increases its level of bound hormone. Goljan also mentions that you'd see the opposite effect in the presence of steroids and nephrotic syndromes. So you could see decreased total T4 but normal free T4 because the bound amounts go down. +