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Old 06-02-2011
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Kidney Post-renal azotemia lab findings

A) could you give the values of:

BUN/CR

FeNa

Urine Na

Urine Osmolality

Urine specific gravity

in a case of post-renal azotemia (post-renal kidney failure)

B) my understanding that I should consider any osmolality beyond 300 as increased (little water-concentrated urine-increased urine gravity) (For both Urine and plasma), and any osmolality under 300 as decreased (excess water) for both of urine and plasma as well ... could you verify this?

c) what is the normal urine gravity ( i understand that it differs depending on what you drink, true, but for USMLE purposes to know the numbers when to assess if its SIADH or DI)

Cheers
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Old 06-02-2011
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i took from me 1 hour to search

Normal Urine specific gravity values are between 1.020 to 1.028.

although the urine osmolality is a more accurate marker of urinary concentration, the specific gravity can be used if an osmometer is not available and if there is no reason to suspect increased excretion of larger solutes. Furthermore, a very low specific gravity (≤1.003) is indicative of a maximally dilute urine (osmolality ≤ 100 mosmol/kg), since there are no causes of falsely low specific gravity measurements.

http://www.uptodate.com/contents/uri...ecific-gravity

normal BUN:Cr is less than 15

patients with normal renal function, the urine osmolality can range from a minimum of 50 to 100 mosmol/kg in the absence of ADH to a maximum of 900 to 1200 mosmol/kg with peak ADH effect.

Normal Urine specific gravity values are between 1.020 to 1.028.


Fractional excretion of sodium (FE-Na) =
100 * ((Urine_Na in mEq/L) / (plasma_Na in mEq/L)) / ((Urine Cr in mg/dL) / (plasma Cr in mg/dL))

(FE-Na < 1%) seen in: pre-renal azotemia and acute glomerulonephritis. Also seen in 5-10% of nonoliguric or x-ray contrast induced ATN, and early sepsis.

(FE-Na > 1% ) Seen in most cases of ATN. Also seen in pre-existing chronic renal failure, and after diuretic administration.

Suggestive of prerenal azotemia or glomerulonephritis:
Urinary Na+ <20 mEq/L
Fe-Na < 1%

Suggestive of ATN or postrenal azotemia:
Urinary Na+ >20 mEq/L
Fe-Na > 1%

http://www-users.med.cornell.edu/~sp...c/fenacalc.htm


To accurately interpret FENa, patients should not have recently received diuretics. FENa is greater than 1% and usually greater than 3% with acute tubular necrosis and severe obstruction of the urinary drainage of both kidneys. It is generally less than 1% in patients with acute glomerulonephritis, hepatorenal syndrome, and states of prerenal azotemia such as congestive heart failure or dehydration. FENa may also be less than 1% with acute partial urinary tract obstruction

normal range of serum osmolality is 285-295 mOsm/kg

http://www.everydayhealth.com/health...e-results.aspx


Sodium in 24-hour urine collection
Normal:40–220 milliequivalents (mEq)/day or 40–220 millimoles (mmol) (SI units)

Sodium in one-time urine sample
Normal:Greater than 20 milliequivalents per liter (mEq/L)
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Old 06-03-2011
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Quote:
Originally Posted by docoftheworld View Post
A) could you give the values of:

BUN/CR

FeNa

Urine Na

Urine Osmolality

Urine specific gravity

in a case of post-renal azotemia (post-renal kidney failure)

B) my understanding that I should consider any osmolality beyond 300 as increased (little water-concentrated urine-increased urine gravity) (For both Urine and plasma), and any osmolality under 300 as decreased (excess water) for both of urine and plasma as well ... could you verify this?

c) what is the normal urine gravity ( i understand that it differs depending on what you drink, true, but for USMLE purposes to know the numbers when to assess if its SIADH or DI)

Cheers
It's important to have paired urine and serum osmolarity. And it is all about concentrating capacity of kidney, and urine osmolarity as miss patho correctly pointed out, can be very wide-ranged.
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thanks guys those questions are important You will see
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Old 07-10-2011
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A 5-month-old boy has a urine output of less than 0.1 ml/kg/h shortly after undergoing major surgery

On examination:

he has generalized edema His blood pressure is 94/48 mm Hg, pulse is 140/mm, and respirations are 20/min

Lab:

His blood urea nitrogen is 38 mg/dL and serum creatinine is 1.4 mg/dL Initial urinalysis shows a specific gravity of 1.018 and 2+ protein Microscopic examination of the urine sample reveals 1 WBC per high-power field (HPF), 18 RBCs per HPF, and

5 granular casts per HPF His fractional excretion of sodium is 3.2%

Which of the following is the most appropriate next step in diagnosis?

A. CT of the abdomen and pelvis
B. Cystourethrography
C. Intravenous pyelography
D. Renal biopsy
E. Renal ultrasonography
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Old 07-11-2011
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A. CT of the abdomen and pelvis
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Quote:
Originally Posted by dryogi View Post
A. CT of the abdomen and pelvis
but why, what are yo expecting from CT. the answer was USG which i couldn't understand, so i put the question here. i think something is wrong with this question......
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Old 07-11-2011
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That questions very confusing (atleastto me it is) im going to try to work it out and can someone critique me on my reasoning/method.


He is oligouric ( but doesnt look like anuric i know in adults anuria still has 100 ml/day excretion not sure about a child though)

his edema and low BP will probably cause a vascular hypoperfusin- ie prerenal failure
BUN :Cr ratio is over 20:1 this makes me think a prerenal / post renal cause
specific gravity = low this makes me think its also a low osmolarity ie dilute urine
2+ protien and 18 RBC in urinte makes me think is some kind of glomerulor problem as Rbc +protien only seen in them

Granular casts though point to Acute tubular necrosis

and to round it off the high FENa- suggest post renal / ATN causes

So taken all together i havent a friggn clue what the hells wrong with him ???
It lookes alot like ATN but then id have to ignore the protien and RBCs

This is a hunch but i have a gut feeling its a stone and for that id do a ultrasound,

Please explain this question somebody
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Old 07-11-2011
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@ bulldozer - didnt the question give an explanation?? where did u get the question from?

and if its USG then it probably is a stone they are talking about
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Old 07-12-2011
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Quote:
Originally Posted by docnas View Post
@ bulldozer - didnt the question give an explanation?? where did u get the question from?

and if its USG then it probably is a stone they are talking about
i agree with you Docnas, i think the pts has obstruction which eventually lead to ATN because his lab tests don't point to single etiology:

BP: low (prerenal azotemia ?)
BUN/CR: 38/1.4 =27 ( prerenal / glomerulonephritis?)
UA: RBC/granular casts
FENa: 3.2% (ATN?)

i think this guy has prerenal azotemia that turned into ischemic ATN , but then why would somebody ask for USG.

the question is from kaplan Qbank: and here is their explanation:

The correct answer is E. This infant developed acute renal failure (ARF) in the immediate postoperative period, as manifested by the increase in blood urea nitrogen and serum creatmme and the decrease in urine output ARF can be classified into prerenal, renal, and postrenal Prerenal causes include hypovolemia secondary to severe dehydration, hemorrhage, and hypotension secondary to shock Renal causes include acute tubular necrosis (ATN), parenchymal disorders (e g , glomerulonephntis), and vascular disorders (e g , renal artery thromoosis or renal vein thrombosis) Postrenal causes include ureteral or urethral obstruction
This infant most likely has ATN, which is caused by ischemic or toxic
injury to the nephrons Ischemia can be caused by hypovolemia, low cardiac output states,
or renal vasoconstriction Toxins include contrast agents, antibiotics, uric acid, and
myoglobm ATN is characterized by mild protemuria, microscopic hematuria, and the presence of coarse granular casts in the urine A fractional excretion of sodium greater than
2% (or 2 5% in neonates) is consistent with renal causes of ARF
Renal ultrasonography is the imaging study of choice for this patient, because it provides anatomic and structural information about the kidneys The study is nonmvasive and can be done easily at the bedside Doppler studies can also be done with ultrasound technology to assess blood flow in the renal vessels, the aorta, and the inferior vena cava.CT of the abdomen and pelvis (choice A} can provide more anatomic details, but it is not a good initial imaging study, especially in this case The contrast dye needed for CT can cause further damage to the kidneys and thus worsen renal failure The same argument applies to intravenous pyelography (choice C).Cystourethrography (choice B} provides structural details of the urinary bladder and the urethra, out it is not indicated in this case Voiding Cystourethrography is indicated in pediatric patients who present with UTI in which retrograde urinary flow is suspected to be the etiology
Renal biopsy (choice D} is the gold standard of diagnosing renal disease, but it is not indicated as an initial study It might be useful in prolonged renal failure with an unidentified cause.







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