Metabolic alkalosis and urine chloride

[OrthoRehab33]

To evaluate metabolic alkalosis you need to examine urine chloride
If urine chloride is low= Vomiting/loop diuretics are the cause. Is this because RAAS is activated in this volume contracted state and you have Na+/Cl- being reabsorbed thus that's why its low?
Why does Hyperaldosteronism cause high urine chloride?

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[Jabbed]

Take a look at Na, K, HCO3 and Cl-. Na and K are right about what we expect (i.e., isosmolar reabsorption does not alter the net concentration. HCO3 decreases significantly because of the active reabsorption via the carbonic anhydrase mechanisms. Why oh why though does Cl concentration actually INCREASE in the tubular fluid of the PCT? Answer: to balance the electrochemical gradient produced by active HCO3 reabsorption.

Now to your point, what happens when there is less bicarbonate to reabsorb (i.e., non-anion gap acidosis)? There is no longer a need for the tubular [Cl] to be so high, so the relative concentration approximates closer to that of Na and K. Physiologically, this results in hyperchloremic metabolic acidosis with decreased urinary [Cl].

 

[OrthoRehab33]

Take a look at Na, K, HCO3 and Cl-. Na and K are right about what we expect (i.e., isosmolar reabsorption does not alter the net concentration. HCO3 decreases significantly because of the active reabsorption via the carbonic anhydrase mechanisms. Why oh why though does Cl concentration actually INCREASE in the tubular fluid of the PCT? Answer: to balance the electrochemical gradient produced by active HCO3 reabsorption.

Now to your point, what happens when there is less bicarbonate to reabsorb (i.e., non-anion gap acidosis)? There is no longer a need for the tubular [Cl] to be so high, so the relative concentration approximates closer to that of Na and K. Physiologically, this results in hyperchloremic metabolic acidosis with decreased urinary [Cl].

Why are you mentioning metabolic acidosis? Conn syndrome produces a metabolic alkalosis. I know ATII causes Na reabsorption in pct which follows HCO3 and Cl like you said would be exchanged to be put in the urine

 

[worldbeater]

If urine chloride is low= Vomiting/loop diuretics are the cause

Correct. The answer is much simpler than the chart above. If you have a metabolic alkalosis, your losing volume and in a low volume state. The profile for serum values in a low volume state are decreased Na, Cl, K and increased pH and blood pressure. If you are losing chloride in your serum, it's going to be higher in the urine as you are peeing it out.

It's seems like a dumb UWorld question to memorize at first, but it makes sense when you understand the physio.

 

[OrthoRehab33]

If you're peeing it out then you're urine Cl would be elevated not low....

 

[worldbeater]

Wow, completely misread that initial urine chloride value. Ignore what I said then. Sorry about that.