Quick Clinical Question

[Requiem]

BUN:SCr ratio - normal 10:1 to 20:1.

If ratio elevates to >20:1, cause is likely pre-renal i.e dehydration.

Why does [BUN] elevate quicker than [SCr] in dehydration since both are measures of concentration?

 

[SpirivaSunrise]

BUN:SCr ratio - normal 10:1 to 20:1.

If ratio elevates to >20:1, cause is likely pre-renal i.e dehydration.

Why does [BUN] elevate quicker than [SCr] in dehydration since both are measures of concentration?

I think it has to do with the size of the molecules (urea vs. creatinine)...so excretion times will differ.

 

[WVUPharm2007]

And as a side note, FENA does NOT stand for ferrous sodium. Trust me.....

 

[no-see-um]

And as a side note, FENA does NOT stand for ferrous sodium. Trust me.....

hahahaha

 

[PharmaSynergy]

BUN:SCr ratio - normal 10:1 to 20:1.

If ratio elevates to >20:1, cause is likely pre-renal i.e dehydration.

Why does [BUN] elevate quicker than [SCr] in dehydration since both are measures of concentration?

Urea is freely filtered by the glomerulus, with about 40-50% reabsorbed by the proximal tubule. The remaining urea is then excreted depending on the rate of diuresis. In a state of dehydration, glomerular filtration rate falls, less urea is excreted, and the [BUN] rises. Urea reabsorption is markedly increased in states of low urine flow. Conditions that reduce renal perfusion leading to a reduction of GFR will therefore cause a disparate increase in [BUN] compared to the [Scr] ... i.e. prerenal azotemia.

 

[Epic]

You kids are way too smart for me.

 

[Requiem]

Urea reabsorption is markedly increased in states of low urine flow.

Excellent. Very helpful!