In this lecture, we’re going to
review renal tubular acidosis.
This is a difficult topic to
address because it’s complicated.
But I’m going to try and
make it as basic as we can,
so we can understand the fundamental
aspects of this disease.
So it’s clear that we worry about
renal tubular acidosis in children
when they have non-gap acidosis but do
not have another cause such as diarrhea.
There are 4 types of
renal tubular acidosis,
types 1, 2, 3 and 4.
In general, you can think of these as
starting as most distal in the loop on Henle
and then going more proximal.
So type 1 is the farthest from the
glomerulus and type 4 is the closest.
I’m going to through these
types of RTA one at a time.
So let’s start with type 1 RTA.
Here is a renal tubule
collecting duct cell.
Remember, this is in the distal part
in the collecting duct of the kidney.
On the left side of the
slide is where the blood is
and on the right side of the
slide is where the urine is,
and the cell is the green box in
the middle that has the alpha.
In fact, this is the alpha
cell of the collecting duct.
Let’s look at what this cell is doing.
So in this alpha cell,
basically what’s happening is nitrogen
is travelling through the cell
and into the urine
in the form of NH3.
But that’s not all that’s happening,
also that NH3 is then binding
with a proton in the urine
and that’s combining to form the ammonia
ion, which is then being peed out.
To get that hydrogen out
of the collecting duct,
we have an ATP-powered proton pump.
So that ATP-powered proton pump is
responsible for getting the hydrogen out,
so that it can then bind with the NH3
which freely travel to the cell.
Additionally, another way
to get the protons out
is through a counter current
This protein which exchanges
a proton for a potassium
which is coming
back into the cell.
Here is the beta cell, this is
another cell in the collecting duct.
In this case, it is
exchanging negative ions
and in particular, it’s extruding a
bicarbonate or HCO3 negative ion
for a chloride negative ion.
So the problem in RTA type 1
is that there is an inhibition of
the activity of this ATP pump.
Essentially, protons are having
a hard time getting out.
This will cause a
Also, however, there is an up
regulation of this particular thing,
the exchange pump between the
bicarbonate and the chloride.
So what exactly is going on here?
Well, there is a mutation in
a gene in primary RTA type 1
or this can also happen
in acquired causes.
Examples would be patients with cirrhosis
or lupus or Sjogrens syndrome
or sickle cell or lithium
or amphotericin exposure.
So we can have primary or secondary causes
of this fundamental problem in
the cortical collecting duct.
Typically in patients with RTA type 1,
they will have a lowish HCO3 level in their
blood, around 15-20 would be expected.
Their urine pH should be high,
they should have basic urine
because they’re peeing out base
retaining acid and becoming acidotic.
Typically because potassium
reabsorption may be impaired,
these children may
have a low potassium.
Also, they may have hypercalciuria
as calcium may go out for the ride
and this can result
in renal stones.
In patients with secondary RTA type 1,
you will see signs to
their secondary disease.
So for a patient with lupus for
example, you might see the malar rash.
In general however, the way you
know a patient has RTA type 1
is that their urine
pH is usually high.
So the treatment is giving them bicitra.
We replace the bicarb that
they were otherwise losing.
Remember, bicitra is simply 2
bicarbonates stuck together.
If these patients do have
a loss of potassium,
we may supplement that,
but that’s not always needed as their
potassium loss is usually not too severe.