Renal Tubular Acidosis (RTA) in Children: Type 2 and 3

00:01 Okay, let’s shift to type 2 RTA.

00:06 Again, a non-gap acidosis, no other known cause.

00:11 So here is this patient’s loop of Henley, the proximal tubule and the cortical collecting duct.

00:18 In this case, you’ll note that while much of the bicarb is lost, it’s either reabsorbed in the proximal tubule or a small percent later on.

00:29 So let’s look closely at that proximal tubule.

00:33 Here is the depiction of what exactly is going on and it has a lot to do with carbonic anhydrase.

00:41 You can look at this and study it in your free time, but the main end of the story is that the problem here in type 2 is a loss of bicarbonate in the proximal tubule of the kidney.

00:54 This system isn’t working and they lose bicarbonate.

00:59 So in a patient with type 2 RTA, if their system wide plasma bicarb is low, they’re going to have a low pH urine.

01:10 However, if their bicarbonate level is normal, they will actually have a normal, like slightly high urine pH.

01:18 In other words, if overlying on a high urine pH to make the diagnosis, they can’t be in a baseline acidotic state.

01:26 If you had a patient with type 2 RTA, for example, who had gastroenteritis and had a little bit of acidosis, this would be a bad time to check their urine pH as a way of making that diagnosis.

01:38 Okay.

01:39 There are many potential causes of type 2 RTA.

01:43 One of the important ones is called Fanconi’s syndrome.

01:48 In this syndrome, patients are not just losing bicarbonate in their proximal tubule, they are losing a whole bunch of stuff.

01:56 This can include not only bicarbonate, but they can lose glucose.

02:00 They can lose uric acid.

02:02 They might lose phosphate or citrate or calcium.

02:06 They may lose potassium, proteins and they may lose amino acids.

02:11 These patients have profound urinary loses.

02:15 What you usually see is that the urine pH is low.

02:21 Okay.

02:22 Causes of Fanconi’s syndrome are multiple.

02:25 They include drugs.

02:27 Drugs that can cause this includes sulfas, acetazolamide which is carbonic anhydrase inhibitor or tetracyclines.

02:36 Patients may have this if they have vitamin D deficiency, if they have received a renal transplant, if they suffer from heavy metal toxicity.

02:44 In some cases, it’s genetic and in adults, this can be caused by multiple myeloma, but we really don’t often see multiple myeloma in children.

02:56 So the management of RTA type 2 includes large doses of bicitra.

03:01 We usually are required to replace potassium because they’re losing all kinds of things.

03:06 And it’s interesting that thiazides may be helpful.

03:09 What thiazides do is they induce the diuresis and therefore raise the proximal tubule threshold for bicarbonate wasting.

03:19 Okay.

03:20 Type 3 RTA, this one will be blessedly brief because it’s exceptionally rare.

03:27 This is a primary carbonic anhydrase deficiency.

03:32 It’s really a combination of type 1 and type 2 RTA and it can result in intellectual disability, cerebral calcifications and osteopetrosis.

03:43 This is so rare in fact that most books completely ignore the existence of type 3.

03:48 I’m really only including it here for complete sake.

03:52 I wouldn’t spend a lot of time studying type 3 RTA.