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

by Brian Alverson, MD

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    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.

    About the Lecture

    The lecture Renal Tubular Acidosis (RTA) in Children: Type 2 and 3 by Brian Alverson, MD is from the course Pediatric Nephrology and Urology. It contains the following chapters:

    • RTA Type 2
    • RTA Type 3

    Included Quiz Questions

    1. All of these answers are correct.
    2. Protein
    3. Glucose
    4. Bicarbonate
    5. Calcium
    1. Loss of HCO3- in the proximal tubules of the kidneys
    2. Loss of H+ in the proximal tubules of the kidneys
    3. Loss of H+ in the distal tubules of the kidneys
    4. Loss of HCO3 – and Cl- in the collecting tubules of the kidneys
    5. Loss of HCO3- in the distal tubules of the kidneys
    1. Multiple myeloma
    2. Carbonic anhydrase inhibitors
    3. Severe vitamin D deficiency
    4. Heavy metal toxicity
    5. Renal transplant

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

     Brian Alverson, MD

    Brian Alverson, MD

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    Excellent lecture
    By Jalil Z. on 09. March 2021 for Renal Tubular Acidosis (RTA) in Children: Type 2 and 3

    Excellent lecture, it's never talked about in our lectures during medical school. Thanks!