Renal Tubular Acidosis (RTA) in Children: Type 4 and Review

00:01 Let’s move on though to a type you do have to know about, which is type 4 RTA.

00:08 Okay.

00:09 Type 4 RTA happens as a result of lack of responsiveness to aldosterone.

00:17 So as we recall, aldosterone causes an activation of a counter exchange mechanism of sodium and potassium.

00:27 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.

00:38 But it’s that pump that’s triggered by aldosterone that is responsible for both retaining sodium in the blood and spitting out potassium.

00:49 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.

01:00 So in type 4 RTA, this counter exchange mechanism is not working correctly.

01:09 Normally, this would hold on to sodium and spit out potassium.

01:15 Now, patients are failing to hold on to sodium.

01:18 They will lose their sodium and they are incapable of spitting out their potassium, so the potassium levels go up.

01:27 So these patients get hyperkalemia which can be life-threatening and hyponatremia from loss of that.

01:38 So the acidosis is actually not really our biggest concern.

01:43 The acidosis is usually reasonably mild and these patients will only have a bicarbonate in the high teens or low 20s.

01:54 There are many potential causes of a type 4 RTA.

01:58 Examples include diabetic nephropathy, congenital adrenal hyperplasia and that’s certainly how we see it most often in young babies and children.

02:08 HIV nephropathy can cause this or it can be from longstanding urinary obstruction.

02:16 This condition can also be caused by drugs.

02:20 Some drugs that can cause type 4 RTA include ACE inhibitors or ACE receptor antagonists.

02:28 NSAIDs can do it.

02:29 Spironolactone, the potassium sparing diuretic can cause it and it can be caused by cyclosporine.

02:37 So our management of type 4 RTA is by necessity, a low potassium diet.

02:45 We also will give children loop diuretics because those are potassium losing diuretics and thus, will essentially be encouraging the loss of potassium.

02:55 Bicitra here is typically not needed because as I said before they’re not really all that acidotic.

03:02 The primary issue is hyperkalemia.

03:07 Okay, let’s review these three major types: Types 1, 2 and 4 together.

03:14 Type 1 is a problem with proton secretion.

03:17 It happens in the distal tubule.

03:21 On labs, you will see a high urine pH, a low serum potassium and you will see high urine electrolytes particularly calcium and potassium.

03:33 This is caused by primary autoimmune diseases, also sickle cell or lithium ingestion.

03:42 Type 2 RTA is a problem with bicarbonate reabsorption.

03:47 This occurs in the proximal tubule.

03:49 Type 2 is closer than type 1.

03:52 In these patients, they will have often an acidic or may be even normal urine pH depending on where things stand.

04:01 The serum potassium will be low or normal and you may find many things abnormal in the urine, especially if they have Fanconi’s syndrome.

04:10 This could include high glucose, uric acid, phosphate, protein, calcium or potassium.

04:17 Again, this can be inherited.

04:20 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.

04:30 Lastly, we have type 4, which is really a problem of aldosterone insensitivity.

04:36 The problem happens in the distal tubule.

04:40 The urine pH is low, but the serum potassium is high and that’s key.

04:47 This can come from a variety of different things such as congenital adrenal hyperplasia, longstanding urinary obstruction, spironolactone use or even NSAID use.

04:59 So that’s a summary of the types of renal tubular acidosis.

05:03 I hope that was helpful to you.

05:05 Thanks for listening.