Distal RTA and serum Bicarb levels

[TrueAntagonist]

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Hey all,
Had a quick question about whether bicarb levels would increase or decrease in Distal RTA.

For a quick refresher, Distal RTA is where the dysfunctional H/K antiport on CT intercalated cell prevents K re-absorption (thus,hypokalemia) and H secretion (thus, metabolic acidosis).

Intuitively, it seems to me that bicarb levels would increase to buffer. However, I've run into a question where a patient with Distal RTA had bicarb levels of 12.

Generally, when I see non-Anion gap Metab acidosis + hypokalemia + low bicarb levels, I think PROXIMAL RTA (where bicarb reabsorption is impaired and, is thus, lost).

Thoughts/corrections/complaints/love-notes?

 

[addo]

Intuitively, it seems to me that bicarb levels would increase to buffer. However, I've run into a question where a patient with Distal RTA had bicarb levels of 12.

in distal RTA, serum HCO3 is buffering the increased acid load that results from the defective H+ secretion... thats why it is low.

in proximal RTA serum HCO3 is low because its being wasted. BTW is hypokalemia characteristic of proximal RTA? I thought it was hyperchloremic acidosis, which is why it results in normal anion gap acidosis

 

[Greenbayslacker]

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[TrueAntagonist]

Awesome. makes sense. Hypokalemia is seen in both distal and proximal. I'm assuming Cl is increasing in both to keep the AG around 12 (to maintain electroneutrality). The reason for bicarbonate decreases in both are different but end result is still non-AG metab acidosis.

Way to tell them apart is 1) severe hypokalemia in distal vs moderate hypokalemia in proximal, 2) urine pH in distal should be >5.5 (hence why CaPO4 stones are seen).


Correct me if I'm wrong.

Thanks again!