NBME 18 HCO3: decreased; inorganic PO4: increased; parathryroid hormone: increased (NBME Answers)

Retired NBME 18 Answers

nbme18/Block 1/Question#10 (reveal difficulty score)
25 yo woman, polycystic kidneys
HCO3: decreased; inorganic PO4: increased; parathryroid hormone: increased 🔍 / 📺 / 🌳 / 📖
tags: renal

+6 upvote downvote
submitted by ∗aneurysmclip(209)

get full access to all content ⋅ pick a username

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

get full access to all content ⋅ pick a username

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. +15

baja_blast I also think there is decreased 1alpha hydroxylation of Vitamin D, which would increase PTH secretion +3

freebie This questions is testing the consequences of renal failure --> "MAD HUNGER" mnemonic in FirstAid +1

+3 upvote downvote
submitted by konkon(3)

get full access to all content ⋅ pick a username

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

get full access to all content ⋅ pick a username

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 +2

+1 upvote downvote
submitted by ∗cbrodo(77)

get full access to all content ⋅ pick a username

Renal damage from PKD can ultimately cause chronic renal insufficiency. This impairs the ability of the kidney to excrete phosphorus and reabsorb HCO3. Elevated phosphate levels in the blood triggers release of FGF-23 from bone, which lowers vitamin D production and decreases calcium absorption in the intestine. The resulting hypocalcemia and hyperphosphatemia will lead to an increase in the secretion of PTH.

get full access to all content ⋅ pick a username

Must-See Comments from nbme18

feliperamirez on He is medically qualified to drive
anechakfspb on Tubular atrophy
aneurysmclip on Endothelial nitric oxide synthase production
azibird on 24,25-Dihydroxycholecalciferol
famylife on Increased transcription of HMG-CoA reductase
match95 on Plasmid loss
apurva on Antineoplastic
cbreland on Basement Membranes
match95 on Proximal tubule: isotonic; Macula densa: ...
sugaplum on Abnormal migration of endoderm from the ...
amirmullick3 on Myelofibrosis
merpaperple on Primary spermatocyte
wishmewell on Alpha-synuclein
namira on Greening reaction on blood agar