Urine Casts: Structure (Nursing)

00:00 I've used the word casts so many times.

00:02 It might be starting to sound weird to you.

00:04 But let me explain why they're called casts.

00:08 It's because of their shape.

00:10 I want you to think of them as molds of where they were formed.

00:13 So you know why they're most likely to form.

00:16 We've got low flow.

00:17 We've talked about those factors.

00:19 But I also want to mention location.

00:22 They're often formed in the distal convoluted tubules, or the collecting duct or the distal nephron.

00:28 Not in the proximal, or the loop of Henle.

00:32 So keep that in mind, we're thinking about the location, it's not in the initial part of it, it's more toward the end.

00:39 Why that matters is it helps healthcare providers diagnose more specifically what's going on in the kidney.

00:46 So they are called casts because of their shape.

00:49 So we know they're cylindrical, because that's the shape of the tubule, where they were formed.

00:54 We know they're most likely to form with urine stasis, low flow, with a low pH, more acidic, and with a higher urine concentration.

01:04 Let's look at the architecture of a cast.

01:07 The Matrix of the cast or the middle of it is made primarily of a mucoprotein.

01:13 Sorry, there's no nice way to say that.

01:15 I mean, just think about it.

01:16 Mucoprotein doesn't sound really lovely, but it's called Tamm-Horsfall.

01:22 So that's the name of that mucoprotein.

01:25 It's secreted by the renal tubules.

01:28 So remember, things are not flowing through there very quickly.

01:31 So this normal substances this normal mucoprotein that in your tubules, its hanging out there for too long, and the conditions are just right.

01:40 And that's why these casts are formed.

01:42 That mucoprotein is what gets hardened.

01:46 Now complete cast has the matrix, which is the mucoprotein, that Tamm-Horsfall protein that's become solidified.

01:53 But it's got other elements.

01:55 Okay, so let me back up.

01:56 Look at that.

01:57 Watch the technical stuff I have for you here.

02:00 There's the matrix of the cast.

02:02 What's it made of? Right. Mucoprotein or Tamm-Horsfall if you want to be more complete.

02:08 Now, ready? Boom! There you go.

02:11 There's the other elements that are embedded in the matrix.

02:15 So what is this telling us about your kidney? "Hey, things are not moving through here very well." So that's why this mucoprotein that's there normally is hanging out for so long, in just the right conditions, that we end up with these casts.

02:31 Casts equal mucoprotein plus other elements that get embedded in it.

02:36 Ready? Okay, cool.

02:38 This is why looking at a microscopic exam, if you see cast, we know we have a problem.

02:44 Because the cast generally maintain the shape and composition as they pass through the urinary system.

02:51 That's what helps us identify specific locations of disease in the urinary system.

02:56 Okay, so let me give you a picture that will help you understand that better.

02:59 Urinary cast can be made up of we know we got the mucoprotein, right and it's hardened.

03:04 But what goes in that? We can have white blood cells, red blood cells, kidney cells, or other substances such as protein or fat.

03:14 So let's give them a name. Look at that.

03:16 The predominant cellular elements determine the type of cast.

03:20 So I have the matrix and if it's decorated or made up of mostly white cells, leukocytes, red cells, erythrocytes, kidney cells, epithelial granular, and Hyaline or fatty.

03:33 So that's how we name the type of casts.