Calculating renal reabsorption! - USMLE Forums
 USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 USMLE Forums Calculating renal reabsorption!

 USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

#1
03-19-2012
 Banned Steps History: Not yet Posts: 176 Threads: 34 Thanked 121 Times in 71 Posts Reputation: 131
Calculating renal reabsorption!

A 35-year-old man with a history of recurrent urinary tract infections comes to the physician because of pain during urination. He is diagnosed and treated for a urinary tract infection. Because of his history, further investigation is warranted. The following data are obtained from the patient:
Inulin clearance

100 mL/min
Plasma osmolarity
286 mOsm/L
Plasma sodium concentration
140 mEq/L
Urine flow
1.44 L / 24 hour
Urine osmolarity
205 mOsm/L
Urine sodium concentration

100 mEq/L

How much sodium does this patient reabsorb each day?
:sorry::sorry:

[A] 14 mEq
[B] 144 mEq
[C] 244 mEq
[D] 20,016 mEq
[E] 20,160 mEq
 The above post was thanked by: Casandra (03-20-2012), venky2600 (09-01-2012)

#2
03-19-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 683 Times in 429 Posts Reputation: 693

if you can tell me wtf a mEq is (something I've never understood) then I can do this question.

1 mEq = how many mOsm?

because once you have that its just

reabsorption = Filtered load - excretion rate = (GFR x [plasma sodium]) - (urine flow rate x [urine sodium])
__________________
"inflammable means flammable!? What a country."
#3
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

how do you get the GFR?

#4
03-19-2012
 USMLE Forums Scout Steps History: Step 1 Only Posts: 51 Threads: 0 Thanked 21 Times in 19 Posts Reputation: 31

Quote:
 Originally Posted by MedPharm how do you get the GFR?
GFR = INULINE clearance

and guys forget about osmolalilty .. we dont need it .. its all about unit conversion witch i haven't practice yet
#5
03-19-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 683 Times in 429 Posts Reputation: 693

Quote:
 Originally Posted by MedPharm how do you get the GFR?
i assume we use 100 or 120 here (since we dont have inulin or creatinine info).
id try both and see which of the answers i get is on the list of options lol
__________________
"inflammable means flammable!? What a country."
#6
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

if all sucks -> use gut-feeling...i'd go with D and move on
 The above post was thanked by: bunny (03-19-2012), d_wiqed (03-19-2012), doctorFH (03-25-2012), Dr. Mexito (03-22-2012)
#7
03-19-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 683 Times in 429 Posts Reputation: 693

Quote:
 Originally Posted by MedPharm if all sucks -> use gut-feeling...i'd go with D and move on
my gut feeling is E lol
__________________
"inflammable means flammable!? What a country."
 The above post was thanked by: MedPharm (03-19-2012)
#8
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

my gut feeling says: dude, you calculated something (that didn't work out) and ended up with XXXX-144 so...last digit is 6 -> wish you good luck with that

me: ok, gut-feeling. as i have no better idea
 The above post was thanked by: Joanna (03-19-2012)
#9
03-19-2012
 USMLE Forums Scout Steps History: Not yet Posts: 36 Threads: 2 Thanked 55 Times in 22 Posts Reputation: 65
ans. D. 20,016 mEq

ans. D. 20,016 mEq

Reabsorption= Filtration - Excretion = (GFR x P) - (U x V)

GFR=100ml/min; P=140mEq/L

U=100mEq/L

V=1.44L/24h

Filtration=GFR x P

=100ml/min x 140mEq/1000ml

=14mEq/min

=14mEq x 1440/24h

= 20160mEq/24h

Excretion=U x V

=100mEq/L x 1.44L/24h

=144mEq/24h

Reabsorption= (20160-144)mEq/24h = 20016mEq/24h
 The above post was thanked by: Ali Khaliq (03-05-2016), Casandra (03-20-2012), d_wiqed (03-19-2012), doctorFH (03-25-2012), Joanna (03-19-2012), MedPharm (03-19-2012), steps_8186 (03-19-2012), terminator (03-19-2012), venky2600 (09-01-2012)
#10
03-19-2012
 USMLE Forums Addict Steps History: Step 1 Only Posts: 106 Threads: 9 Thanked 74 Times in 43 Posts Reputation: 84

my gut-feeling in a mathematical genus
 The above post was thanked by: d_wiqed (03-19-2012), Hitman (03-19-2012), hope12 (05-02-2012)
#11
03-19-2012
 USMLE Forums Guru Steps History: Step 1 Only Posts: 443 Threads: 54 Thanked 268 Times in 159 Posts Reputation: 278

great problem
just dont look at osmolality
gfr=inulin clearance=100*140
but look at the units
its in ml,min
so convert it
GFR=(100*140*60*24)/1000 and unit is meq/Day
now excretion is(1.44*100)=144meq/day
absorbed=filtered -excreted=20016meq
 The above post was thanked by: Ali Khaliq (03-05-2016)
#12
03-21-2012
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,406 Threads: 118 Thanked 683 Times in 429 Posts Reputation: 693
help!

guys, im really confused

as i see it, it is:

reabsorption = (V x Ux) - (GFR x Px)
=(140x144) - (100x286)
=28700 - 28600
=100

im way off, where am i going wrong :/
__________________
"inflammable means flammable!? What a country."
#13
03-22-2012
 USMLE Forums Guru Steps History: 1 + CS Posts: 303 Threads: 57 Thanked 109 Times in 69 Posts Reputation: 119

this is a question from kaplan q bank
a typic wtf type questions...i kept scratching my head
while doing this for 5 min i tried and then gave up and got the next few questions also wrong as i ran out of time
#14
03-22-2012
 USMLE Forums Addict Steps History: Not yet Posts: 138 Threads: 1 Thanked 53 Times in 32 Posts Reputation: 63

Quote:
 Originally Posted by Dr.NickRiviera guys, im really confused as i see it, it is: reabsorption = (V x Ux) - (GFR x Px) =(140x144) - (100x286) =28700 - 28600 =100 im way off, where am i going wrong :/

reabsorption = (GFR x Px) - (V x Ux)

GFR= 100 mL/min= 144 l / 24 h
Px = 140 mEq/L

GFR X Px = 144 x 140 = 20160

V = 1.44 l/ 24 h
Ux = 100 mEq/l

V x Ux = 144 mEq

20160 - 144 = 20,016 mEq
#15
03-06-2017
 USMLE Forums Scout Steps History: Not yet Posts: 16 Threads: 7 Thanked 8 Times in 2 Posts Reputation: 18

GFR= 100ML/min (convert this to L = 0.1L/min)
V= 1.44L/24 hours (convert this to per min = 1.44/1440mins = 0.001)

resorption= filtered - excretion
resorption = (GFR x Px) - (V x Ux)

resorption= (0.1 x 140) - (0.001 x100)
=13.9 or 14.

#16
03-09-2017
 USMLE Forums Scout Steps History: Not yet Posts: 10 Threads: 3 Thanked 0 Times in 0 Posts Reputation: 10

Answer is D. Just subtracting the amount excreted from the filtered load.
Amt absorbed = Filtered load - Amt excreted
= GFR x Plasma concn - Urinne flow rate x Urine concn
(GFR= 100ml/min = 100x1440 /1000 =144 L/day)

Amt absorbed = 144L/dayx140meq/l - 1.44L/dayx100meq/l
= 20016 meq/day

 Tags Physiology-, Renal-, Step-1-Questions

Message:
Options

## Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
User Name:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
 AMG IMG ---
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
Favorite USMLE Books
 What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
 Where you live. Leave blank if you don't want to tell.

## Log-in

 Similar Threads Thread Thread Starter Forum Replies Last Post sfsheran USMLE Step 1 Forum 1 03-12-2012 07:32 AM sana akbar USMLE Step 2 CK Forum 1 12-01-2011 11:54 AM docnok USMLE Step 1 Forum 1 11-10-2011 07:13 PM sandy_presto3 USMLE Step 1 Forum 2 07-22-2011 02:48 AM

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2019)