in this video I'll teach you everything that you need to know about urinary casts urinary casts are very high yield for USML elite and complex and they are one of the buzzwords or findings that show up on exams that help test writers create challenging third order questions so if you're able to identify the buzzwords and the associations with urinary cast you can get a lot of free points so let's start with an overview a urinary cast is a cylindrical tube-shaped structure in the distal convoluted tubule and the collecting duct of the kidney now typically these suggest either glomemeular or renal tubular disease but I would note that some are benign and if you see certain types of casts and we'll get into this more in just a moment that can be normal all casts rely on the presence of a mucoprotein base with varying elements attached to it and that mucoprotein base is called a tam horsefall mucoprotein sometimes you'll see this written out as euromodulin but tam horsefall and euromodulin that means the same thing this is present in all casts and this can be a little confusing for medical students because some of you only associate that with one type of cast but truly the base of all of these urinary casts is euromoduline or TAM horsefall protein and this is produced in the ascending loop of henley so before we go any further I just want you to understand that basically if you're asked what is a cast explain a cast to me like I'm five the answer is that a cast is basically a trapped coagulated mucoprotein plus other cellular content structure and it originates in the lumen of the distal convoluted tubule or the collecting duct it can be seen in normal physiology but on your exam it's generally going to be seen when there's some type of kidney injury or alteration in pH or urinary concentration so now that we understand what a cast is let's talk about how a cast is formed so in general you're going to have on your exam urinary stasis this could be due to various different reasons right it could be due to some type of kidney injury it could be due to acute tubular injury or acoustis it could be due to glomemeular nephritis but something happens and we don't worry yet about what that something is which causes urinary stasis once we have urinary stasis that increases osmolality once we have an increased osmolality we have increased sodium and calcium concentrations when that happens our pH drops and when our pH drops we get increased levels of tamorfall mucoprotein also known as euromodulin now again tamorfall mucoprotein aka euromodulin this is present in normal urine but it's when that level increases beyond normal physiological levels that the TAM horsefall mucoprotein will coagulate and attach to other trapped contents within the tubular lumen that shouldn't be there and we'll get to that when we talk about cellular casts and then you get these urinary casts forming so let's go through the different types of urinary casts one at a time i'll give you a brief overview and if there's a pneummonic that I have to help you memorize the association between the urinary cast and the disease state I'll point that out so let's start with a highland cast now highland casts are the most most common type of urinary cast and they are one of the cast that you can see in healthy normal individuals these are composed of TAM horsefall mucoproteins which again I told you is in normal urine now I want to pause for a second because this is a topic of great confusion for medical students when you look through various textbooks and uh resources that you might be using to study oftentimes you see TAM horseville mucal protein listed as an association an association with a highland cast and that's correct most like 95% or something close to that of a Highland cast is made up of TAM horsefall mucro protein however I want you to understand the TAM horsefall mucoprotein is in every cast it just makes up the overwhelming majority of a highland cast and that's why when you're studying you classically associate TAM horsefall with highin so on your exam if they tell you in the vignette that they looked at a urinary cast under a microscope and they determined that it was mostly made up of TAM horsel mucoprotein chances are that you're dealing with a highland cast but please note that for real life and for your exam every single cast is going to have Tam Horswell mucoprotein it's just that highin has it in a really high ratio so the highland cast is composed of our euromodulin or our TAM horse mucoprotein now normally in the urine that serves a lot of good physiological functions one of which includes preventing urinary tract infection now just briefly the renal tubular cell secretes the tamorph in response to low urine flow concentrated urine or acidic urine pH so it's actually like a normal defense initially and it's found in states of dehydration or strenuous exercise it's also common in chronic kidney disease and patients who are taking diuretics but because the TAM horses mucoprotein gets excreted in states of dehydration or strenuous strenuous exercise that is the reason why hyelin casts are very common in normal individuals who are exercising or weightlifting or running a marathon and that sort of thing now these will appear cylindrical they're clear and they're very difficult to see under a microscope so if you're taking your exam and they show you a picture and it's like you see something there but it's almost invisible that's probably a Highland cast you don't really have to worry about images for cast but I would just know that because sometimes on the stupid really experimental questions the images do show up now with Highland Cast what you need to take away from this is that one it's normal two it's highly composed of TAM horseville mucoproteins to an extent much greater than any other urinary cast and it's seen in individuals who are dehydrated and exercising and that's why it's quote unquote normal so I want you to use my pneummonic that highin cast in high exercise individuals hy for high hy for hyelin cast if you can memorize that that's really all you need to know for us and commlex as far as hyelin casts go now let's talk about granular cast so granular casts are the second most common type of cast and these are formed from the breakdown of cellular casts and when I say cellular cast I mean like red blood cell casts white blood cell casts epithelial cell casts and we'll talk about those individually in just a moment but for granular casts these usually represent urinary stasis in the nephron and unfortunately that doesn't tell you a whole lot about a disease association but granular casts can be found in pyon nephritis acute tubular necrosis glomemeulo nephritis and nephroclerosis now I want to point out that muddy brown cast which we're going to talk about on the next slide right after this one these are muddy brown is actually a subtype of granular and it's much more high yield to know about a muddy brown cast than it is to know about a granular cast so for the purposes on your exam there's really not anything you need to know about granular i would just know that they exist and that they have a lot of different associations disease-wise but as you'll see the associations that can be with granular casts are a lot higher yield and more associated with other casts and for that reason granular is really not one that I think is worth memorizing for us and complex as far as its appearance it's cigar- shaped it has a highin matrix with with mixed cellular debris and its refractive index is quite high again I don't think you need to memorize anything here let's just talk about the important subtype of granular cast that's the muddy brown cast so this is a subtype as I said of a granular cast it is very dark and as you can see in this image here you can probably appreciate that that is darkly pigmented which if you compare that to an image of a highland cast or go ahead and Google what a highland cast looks like this is significantly darker now you want to associate muddy brown cast with acute tubular necrosis or ATN and you'll be like "Whoa whoa whoa Dirty my boy you said on the last slide that acute tubular necrosis can be associated with granular." And now you're telling me that I need to memorize it with muddy brown yeah unfortunately when it comes to urinary cast there is a lot of overlap but if you have to take a guess and you have to pick one answer based on what cast you you're given you want to associate muddy brown with ATN and the reason that we do that is because the dark pigmentation that you see in muddy brown and the the reason that the muddy brown casts are forming to begin with is because you have the presence of tubular injury and of all the different disease processes the one that is most highly associated with acute tubular injury is of course acute tubular necrosis the dark brown muddy color that you see here we think that's due to mitochondrial pigment or lipopus skin that basically leaks out when you have a acute tubular necrosis but that is a bit more theoretical bottom line here muddy brown equals ATN so my pneummonic is that I associate mud with driving an ATV right people drive ATVs through the mud for fun so ATV kind of sounds like ATN and MUD ATV MUD ATN muddy brown ATN acute tubular necrosis so that's the easy way to memorize this but bottom line here when it comes to muddy brown casts which again are a subt type of granular cast you got to associate that with acute tubular necrosis now let's talk about fatty casts fatty casts are formed by the breakdown of lipid rich epithelial cells so essentially these are like a highland cast that has an oval fat body inclusion and that buzzword that oval fat body that's become very buzzy on exams so if you see that that is telling you you're dealing with a fatty cast now the other thing that the exam writer really likes is what's called the maltes cross sign so because of the way that the fat droplets look under polarized light if you look at my image here this is said to look like a Maltese cross so if you see that image it's very unique it's very specific for a fatty cast these appear round and they're variable in size which is important because if you look at the image of them some people think that they look a lot like red blood cell cast but the fact that these are variable in size helps you differentiate that against the red blood cell cast which appear more uniform in size now these are associated strongly with nefertic syndrome and if you've done your studying in the renal chapter you know that one of the key findings of nefertic syndrome is all these lipid changes and these things having to do with fat so it should not come as a surprise to you that fatty casts right literally the only cast with fat in the name are associated with nefertic syndrome so you really really want to memorize that fatty and nefertic go together now my pneummonic to memorize that is instead of nefertic I think nefratic or nefatty so nefatty syndrome or nefratic syndrome if you if you will and that helps me memorize that fatty casts equals nefertic syndrome now let's talk about waxy casts so waxy casts are formed by latestage degeneration of granular cast so granular casts came first then they degenerated and they turned into waxy and this represents renal stasis and you're like you got to at this point in the video you're like dude I don't understand you're like you're telling me that renal stasis is present in this cast and renal stasis is present in this cast and if the the kidney gets punched it's going to form both of these cast yeah there's overlap that's the unfortunate reality of this topic but waxy casts are associated with long-standing and endstage renal disease and to be clear on your exam if the test writer wants you to pick a waxy cast they're going to give you a patient who's had chronic kidney disease stage four or stage five for years and I mean like 10 plus years so they're not going to give you an acute renal pathology they're going to give you long-standing chronic kidney disease and then that will point you in the direction of a waxy cast how this looks is it's highly refractive with dark borders it's homogeneous and it has quote sharp broken off ends and indentations that's a buzzy description because no other cast looks like that so if you see anything about being sharp or broken or indented that's waxy that's going to wax so these are waxy casts not a whole lot to know here other than waxy equals longstanding kidney disease so less of an acute pathology more of your elderly patients who have CKD stage 345 that sort of thing now let's talk about red blood cell cast so I want to pause and point out that now we're talking about a cellular cast which is to say that the cast has cellular components within it and you see a cell in the name right red blood cell cast so we're talking about cellular casts so these are formed when when the red blood cell accumulates in a protein matrix after leaking out of the glomemeulus so basically what happens here is that in a state of either glomeular nephritis or vascular disease you have red blood cell leakage and when you have red blood cell leakage then you have the coagulation of the red of the cell type in this case the red blood cell in that protein matrix and that's why you get red blood cell casts so because of that these are highly associated with different types of glomemeulfritis and vascular disease such as granulomattosis with polyangiitis lupus postre glomephritis good pastor syndrome and hypertensive emergency how these look is that they will be by conclave red blood cells with dark stained hemoglobin so bottom line here red blood cell cast equals glomemeular nephritis and vasculitis that's what you need to memorize here vascular disease and glomemeular nephritis now let's differentiate that against a white blood cell cast a white blood cell cast is formed when white blood cells accumulate inside of a protein matrix in the tubular lumen so very similar to our RBC's our WBC's you know they're present they leak out they coagulate they mix with the protein matrix and you get white blood cell casts now these are associated with high states of intrarenal high inflammation and in the the two most common that you absolutely need to memorize are pyonfritis and interstitial nefritis those are the big two but I would also point out that occasionally I've seen some challenging questions where you have to identify WBC cast in transplant rejection but if you only have the brain space for two memorize interstitial nefritis and pyo nephritis these have sharp these have central nuclei with sharp margins and they also can can contain multilobed cells again we're dealing with a derivative of a white blood cell so some of the natural anatomy of that cell kind of gets pulled into the cast and that's why you see multilob cells with sharp margins and central nuclei so WBC's equal interstitial nephritis and pyonfritis now let's conclude with epithelial cell casts so these are formed when descated epithelial cells of the tubial lining kind of sloth off and end up coagulating these are associated with conditions where obviously the tubular cells will be sloed off because how could you form an epithelial cell cast if the cells never fall off to begin with so these are associated with various disease processes and this can be a little bit confusing because it's associated with interstatial nefritis acute tubular necrosis and proliferative glomemeular nefritis all of which you've seen associated with other types of casts so the really what'll get you to move in the direction of an epithelial cell cast is either they're going to focus highly on a tubial injury where again those tubular cells which are going to be epithelial will be sloed off or they're going to describe the anatomy or the form that you're seeing and they're going to use the word sheets so these appear in sheets or clumps of tub tubular cells and they are in multiple layers so that that description is pretty unique for epithelial cell casts now the thing I want you to understand is that whether you're dealing with epithelial cell cast as a result of acute tubular necrosis or you're dealing with a muddy brown cast as a the result of acute tubular necrosis you want to associate the various causes of a t of acute tubular necrosis with these casts and this is a good opportunity for the test writer to give you a third order question because they could basically describe for you either the epithelial cell cast or the muddy brown cast essentially hint to you that you're dealing with acute tubular necrosis and then ask you for the ideology so you got to remember that when it comes to acute tubular necrosis you have eskeemic ideologies and nephrotoxic ideologies and when we talk about es schemic ideologies we're talking about things like hypoalmia and sepsis when we talk about nephrotoxic ideologies which is probably what they're going to give you on your exam we're talking most often about drugs and drugreated causes so things like your amoglycosides uh if somebody gets is getting imaging done and they're given contrast right remember that that can be nephrotoxic in the case of epithelial cellcast they like to associate acute tubular necrosis with toxic ingestion of either heavy metals or things like ethylene glycol uh or the presence of urate crystals from tumorlyis syndrome so just associate all of these ideologies with downstream acute tubular necrosis because I've seen test writers essentially give you a question describe somebody who was treated with an amoglycosside and then they'll say oh and this is in the urine and you're you're now you're like oh it's a muddy brown cast so what's going on here the answer is acute tubular necrosis there's been challenging questions that have popped up where they'll give you somebody who has a heavy metal exposure and now you have something in the urine appearing in sheets and you got to be like "Oh that's an epithelial cell cast i got to work backwards i'm probably dealing with acute tubular necrosis uh due to toxic ingestion of some type of you know toxin." And it's you got to your brain has to be able to make those third order connections so those are your epithelial cellcasts let's wrap up with a really really simple high yield table you're like "Dude I don't care about anything you said for the last 10 minutes tell me the short and sweet of what I should memorize." And here's my answer so Highland cast equals non-specific in healthy individuals exercise states granular muddy brown just remember that for muddy brown acute tubular necrosis muddy brown is a subtype of granular granular is not worth memorizing fatty cast equals nefertic syndrome white blood cell cast equals interstitial nefritis and pyonfritis red blood cell cast equals equals glomeular and vascular disease there's lots of different causes there epithelial cell cast not worth memorizing because there's some overlap with muddy brown but heavy metal exposure and acute tubular necrosis also in epithelial cast but probably not worth memorizing because it's too confusing and then waxy is going to be your longstanding kidney disease so it can be AKI but more commonly we're talking about chronic kidney disease and endstage renal disease so if you don't care about this topic and you just want to spend two minutes on it this is the table to memorize but if you do care and you want to get the perfect score on your test re-watch this video a few times good luck