[lemontea88]

Hey guys,

Could you help me out here. I don't seem to get the method to relate urine sodium level to whether it is a concentrated urine or dilated urine.

Example of a case of SIADH :
Serum osmolarity = 268 mOsm/kg and urine sodium level is 40 mEQ/L
The explanation to this question says that there is extensive renal salt wasting.

How do you see if there is extensive salt wasting or not? The lab reference values say urine sodium "varies with diet". What??

 

[khanar]

Usually they talke about 20 meq/L as the cut off level, normally less than this. Regardless of patient diet.

In SIADH, the urine contains high Sodium >40 meq/L which is inappropriate in the context of hyponatremia.

 

[lemontea88]

Ahh I see.. so I guess this means whenever we see urine sodium more than 20 meq/L, we can assume most likely it is concentrated?

How bout dilute urine? Any cut off point?

 

[Sabio]

Why Increased Sodium Excretion in SIADH

I just want to explain the reason why there's natriuresis in SIADH as this often is confusing and counter-intuitive

In SIADH, there's ECF volume expansion this result in
1- Decreased Aldosterone secretion thereby more Sodium is lost in urine.
2- Increased Atrial Natriureteric Peptide (ANP) again leading to increased Sodium excretion.

 

[khanar]

Ahh I see.. so I guess this means whenever we see urine sodium more than 20 meq/L, we can assume most likely it is concentrated?

How bout dilute urine? Any cut off point?

Less than 20 meqs per liter is dilute urine
More than 40 meqs per liter is concentrated urine
This is one of the ways we differentiate between pre-renal and renal azotemia

 

[Brain Power]

Beautiful!!

I just want to explain the reason why there's natriuresis in SIADH as this often is confusing and counter-intuitive

In SIADH, there's ECF volume expansion this result in
1- Decreased Aldosterone secretion thereby more Sodium is lost in urine.
2- Increased Atrial Natriureteric Peptide (ANP) again leading to increased Sodium excretion.

AMAZING!! i was dying to find an answer to this question! im finally so happy :happy: