Let’s move on though to a type you do
have to know about, which is type 4 RTA.
Type 4 RTA happens as a result of lack
of responsiveness to aldosterone.
So as we recall,
aldosterone causes an activation
of a counter exchange mechanism
of sodium and potassium.
The sodium is also getting out back into
the blood through just a general channel
and the potassium is balanced by going
back into the urine through two channels.
But it’s that pump that’s
triggered by aldosterone
that is responsible for both
retaining sodium in the blood
and spitting out potassium.
Many people think of aldosterone as having
a primary role of potassium homeostasis
rather than sodium or hanging on to water,
although it obviously has both roles.
So in type 4 RTA, this counter exchange
mechanism is not working correctly.
Normally, this would hold on to
sodium and spit out potassium.
Now, patients are failing
to hold on to sodium.
They will lose their sodium
and they are incapable of
spitting out their potassium,
so the potassium levels go up.
So these patients
which can be life-threatening and
hyponatremia from loss of that.
So the acidosis is actually not
really our biggest concern.
The acidosis is usually reasonably mild
and these patients will only have a
bicarbonate in the high teens or low 20s.
There are many potential
causes of a type 4 RTA.
Examples include diabetic nephropathy,
congenital adrenal hyperplasia
and that’s certainly how we see it most
often in young babies and children.
HIV nephropathy can cause this
or it can be from longstanding
This condition can also
be caused by drugs.
Some drugs that can cause
type 4 RTA include
ACE inhibitors or ACE
NSAIDs can do it.
Spironolactone, the potassium
sparing diuretic can cause it
and it can be caused
So our management of type 4 RTA is by
necessity, a low potassium diet.
We also will give children loop diuretics
because those are potassium losing diuretics
and thus, will essentially be
encouraging the loss of potassium.
Bicitra here is typically not needed
because as I said before they’re
not really all that acidotic.
The primary issue is hyperkalemia.
Okay, let’s review these three major
types: Types 1, 2 and 4 together.
Type 1 is a problem with proton secretion.
It happens in the distal tubule.
On labs, you will see a high urine pH,
a low serum potassium
and you will see high urine electrolytes
particularly calcium and potassium.
This is caused by primary
also sickle cell or
Type 2 RTA is a problem with
This occurs in the
Type 2 is closer than type 1.
In these patients, they will have often
an acidic or may be even normal urine pH
depending on where things stand.
The serum potassium
will be low or normal
and you may find many things
abnormal in the urine,
especially if they have
This could include high glucose, uric acid,
phosphate, protein, calcium or potassium.
Again, this can be inherited.
It could be as a part
of Fanconi’s syndrome,
which can be caused
by a number of things
including for example rickets
or heavy metal toxicity.
Lastly, we have type 4, which is really
a problem of aldosterone insensitivity.
The problem happens
in the distal tubule.
The urine pH is low, but the serum
potassium is high and that’s key.
This can come from a variety
of different things
such as congenital
longstanding urinary obstruction,
or even NSAID use.
So that’s a summary of the types
of renal tubular acidosis.
I hope that was helpful to you.
Thanks for listening.