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NBME 18 Answers

nbme18/Block 1/Question#10 (15.6 difficulty score)
25 yo woman, polycystic kidneys
HCO3: decreased; inorganic PO4: increased; parathryroid hormone: increased🔍

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basically polycystic kidneys won't work properly, they've hinted at this with the s.creat of 4mg/dl. thus the kidney won't do what its supposed to do. REMEMBER to check whether they are asking SERUM changes or URINE changes

Kidneys normal function - reabsorb HCO3- , its not doing that now > decreased HCO3

PTH - would cause increased Calcium reabsorption in kidneys, but kidneys aren't able to reabsorb calcium > PTH responds to low calcium levels and levels increase

PO4 ties into PTH as well, PTH acts be DECREASING PO4 reabsorption. Since kidneys aren't working ie: not responding to PTH > there would be increase in PO4

pg32  Sometimes these questions are made more difficult by trying to decipher the order in which these changes happen (first cause). In my mind, whenever I see a question on renal insufficiency, I know that phosphate in the serum will increase. In response, Ca will decrease and in response to that, PTH will increase. Lastly and unrelated, HCO3 will decrease because the kidneys aren't absorbing HCO3 as they usually do. +6  

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submitted by konkon(0),

I got this one wrong. I thought there is hyperkalemia which leads to alkalosis

hellhellhell  Hmm +  
itsalwayslupus  If you look at FA 2019 p. 590 under Consequences of Renal Failure ("MAD HUNGER"), there is hyperkalemia and a metabolic acidosis +  

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submitted by cbrodo(45),
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