How do you evaluate type II RTA? Again, hyperchloremia, metabolic acidosis. But the anion gap is negative. Remember I told you that for distal RTA the anion gap was positive. This one is not a problem with making ammonia. This is a problem just with leaking lots of bicarb. So the anion gap is negative. The urine pH is greater than 5.5 when the plasma bicarb is what is normal to you and me, but when the plasma bicarb falls below the threshold, the urine pH is low.
I am going to … this is another way to evaluate it. Again, this is something that pediatric nephrologists do. It’s a fractional excretion but instead of a fractional excretion of sodium, it’s a fractional excretion of bicarbonate. And we can do this, and this allows us to do that. Again, they will not be asking you that.
A quick word about type IV RTA. There is no type III. There was a mistake. Somebody made a mistake and so they called… we called just type IV. Type IV is so-called low-renin hypo-renin hypoaldosteronism. This again is a non-anion gap acidosis but it has hyperkalemia. Urine pH can look like type II RTA with a pH less than 5.5. Highly unlikely that they will ask you about this. Very unusual. It’s caused by true aldosterone deficiency, conditions which decrease renin secretion and conditions where the kidney cannot respond to mineralocorticoids. This is a reiteration; the diagnostic workup of suspected RTA. We look first for he serum anion gap. We see whether it is elevated. The metabolic acidosis is elevated. If it is you work up for a gap acidosis. If there is a normal gap, you want to evaluate for RTA. Then I put in how you go with RTA’s, either type II or type I and type IV. I’m going to skip over this, and I’m going to skip over metabolic alkalosis except to remind you that the laboratory studies for metabolic alkalosis will show you that besides a blood pH that is high, there is a low chloride, a low potassium, increased bicarbonate or CO2 in the blood. The few physical signs; tetany. Underline tetany and convulsions. This is one of the things that can give you tetany and convulsions, metabolic alkalosis.
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