[memory]

what is the mechanism of renal tubular acidosis being a normal gap metabolic acidosis? please be so kind as to explain.
thanks in advance

 

[Ahmed-USMLE]

• anion gap = Na - Cl and HCO3
• metabolic acidosis means low bicarb

Therefore, in any metabolic acidosis you'll have increased anion gap unless the chloride compensates for the depressed bicarb.
Therefore, any normal anion gap metabolic acidosis is essentially hyperchloremic metabolic acidosis. See normal anion gap mnemonic thread

In proximal renal tubular acidosis you have failure of bicarbonate reabsorption and this will be compensated by chloride reabsorption to maintain neutrality across the renal tubule membrane. See this thread for a similar issue

 

[memory]

• anion gap = Na - Cl and HCO3
• metabolic acidosis means low bicarb

Therefore, in any metabolic acidosis you'll have increased anion gap unless the chloride compensates for the depressed bicarb.
Therefore, any normal anion gap metabolic acidosis is essentially hyperchloremic metabolic acidosis. See normal anion gap mnemonic thread

In proximal renal tubular acidosis you have failure of bicarbonate reabsorption and this will be compensated by chloride reabsorption to maintain neutrality across the renal tubule membrane. See this thread for a similar issue

thank you. what i really want to know is what is the mechanism for hyperchloremia. in rta. is an ion pump involved?

 

[Ahmed-USMLE]

thank you. what i really want to know is what is the mechanism for hyperchloremia. in rta. is an ion pump involved?

Yes, in the proximal convoluted tubules you have 60% reabsorption of Sodium and that's coupled with 15% bicarb and 45% Chloride absorption to maintain electrical neutrality.
When that 15% bicarb decrease (such as Type II RTA) then the 45% Chloride absorption increases and there you have the hyperchloremia.

 

[memory]

Yes, in the proximal convoluted tubules you have 60% reabsorption of Sodium and that's coupled with 15% bicarb and 45% Chloride absorption to maintain electrical neutrality.
When that 15% bicarb decrease (such as Type II RTA) then the 45% Chloride absorption increases and there you have the hyperchloremia.

thanks a million for this. it makes perfect sense.

 

[khanar]

urine anion gap is also important

Just wanted to add here that in RTA you also have something called the urine anion gap.
The urine anion gap = (Na+) - Cl-
In RTA because we fail to excrete NH4Cl then we have low chloride in urine the urine anion gap is positive unlike the other causes of normal anion gap acidosis (such as diarrhea) where have a negative urine anion gap