Transcript: What Causes Low Sodium? Hyponatremia Workup (Lab Interpretation for New Nurse Practitioners)

​Liz Rohr:
Hey, there, it's Liz Rohr from Real World NP and you're watching NP Practice Made Simple. The weekly video to help save you time, frustration and help you learn more faster so you can take the best care of your patients. So today I'm going to talk to you about low sodium hyponatremia, which is pretty common in primary care. It's a little bit of a mind-bending topic because it has to do with renal physiology, but I've really broken it down and made it really super simple.
 

And I've also led you through the most common reasons that you'll see in primary care. I've done an extra kind of bonus slide that talks about following down that rabbit hole of workup if you're in a more higher acuity setting like internal medicine or a long-term acute care. But most of the time, majority of the time in my four years of primary care, it's been the first couple of steps will lead you to your kind of etiology for the low sodium and help you with that workup and plan. So without further ado, I'm going to share my screen with you.
 

All right. So here's the case study on hyponatremia. So Jim is a 61 year old man. He's reestablishing care with a new PCP. He's been at this clinic for a number of years, but his doctor just left and I'm taking over. This is a recent patient. And again, this is not his real name or his photo. So he doesn't do what he's supposed to do. He kind of opened the visit like that, which kind of sets the stage. So he does take his blood pressure medications, which is great. He drinks a six pack of beer a day, and then he smokes one pack a day and he's done so for about 50 years. And I think that's kind of what he's referring to when he says he doesn't do what he's supposed to, but also he only drinks about eight ounces of water or less per day.
 

So he's not taking super great care of himself. He's not really eating that consistently either. And he's not interested in cutting down or quitting either the alcohol or the tobacco. So his past medical history is significant for high blood pressure, emphysema, alcohol use disorder and diverticulosis remotely. He's got no past surgical history or family history that he knows of. He's taken chlorthalidone 50 milligrams. So if you're not familiar with this medication, it's in the thiazide diuretic family, it's really potent. And it actually has really strong evidence for mortality protection in terms of if you're going to be choosing a thiazide for blood pressure management. So today his blood pressure in this visit was 144 over 80, heart rate was 100, oxygen 98%, BMI is 24, so he's on the slimmer side. And he says that he's going on a drinking weekend this weekend with his friends. And I really appreciated how forthcoming he wasn't honest.
 

So the plan today, I'm going to focus on hyponatremia, but I'm going to touch on the other components of holistic care at the end. So to start, I'm going to check some labs. So a CBC and a CMP, and that's to get a baseline function of his liver, his kidneys, and any signs of anemia related to the alcohol use disorder. I'm going to check out hemoglobin A1C, which is a diabetes screening test. According to the USPSTF guidelines. I'm also going to check a thyroid function study, a TSH, and then I'm going to check his lipid panel again in accordance with the USPSTF's screening guidelines, according to his age. So here are his lab results. So just to start, his CBC is normal and his cholesterol and lipids are also normal, which I was pleasantly surprised by.
 

And this page is going to have a, BMP, the basic metabolic panel spliced with the liver function panel and the TSH and the A1C just to fit it all on one slide. So the glucose is normal. The BUN, creatinine and GFR are showing normal kidney function. His sodium is low 134. So the normal range from my lab is 137 to 145. And it really just depends on the laboratory that you're using, what the normal reference range is. So additionally, his potassium and his chloride are also low. Potassium is 3.3 with a normal range of 3.5 to 5.3. And the chloride is 92 with a normal range of 98 to 110. So in the second column here, I've got the calcium and then I've got the liver function panel, and those are all normal shockingly because of his heavier alcohol use, the AST and ALT are normal and the ALK PHOS.
 

So surprise here, the TSH is 5.77. I didn't expect that. That was a screening test. And the A1C luckily is normal at 5.6. So hyponatremia, the one thing I want you to think about when it comes to hyponatremia, the really kind of like baseline conceptual knowledge here is that you're holding onto more water than you're getting rid of. So your body is a vessel with water and salt, and if you add too much water and you're not getting rid of enough, that sodium concentration is going to go down and that's the kind of the basic way to conceptualize hyponatremia. So it's really more about water than it is about salt. So I'm going to use the benefit of repetition, because this can be a little bit of a tough topic, so I'm just going to introduce the three kind of main reasons we get low sodium.
 

And this has to do with how the kidneys function just in their normal physiologic baseline, as well as how they're functioning. Are they normal? Are they in any kind of renal impairment status. The second thing to think about is intake of salt and or water. And the third thing to think about is a hormone ADH, the antidiuretic hormone, and whether it's working or not. And that's a little bit of a... Just stay away from me for a second. And I'm going to get more into that.
 

Okay. So the first three steps to a hyponatremia workup. Number one, is it truly low? And I love this because if you saw the last case presentations that I did on high potassium and high calcium, this is also the first step for those too. Is to really validate, is this actually a lab test that we can trust as being actually lower, or is it artifact.
 

So fun fact, when you think about sodium after thinking about that first kind of tenant of it's really more about water than it is about salt. The second thing I want you to think about is glucose, because this is the number one thing I see in primary care that glucose artificially lower sodium, and that has to do with the concentration of the blood. So that when you have a super high glucose level, your sodium is going to go down to compensate for that. So there's a sodium correction score. So whenever you see a sodium that's low, the first thing I want you to think of is glucose, and then enter in that correction score, if it is a high glucose. The other thing to think about is that lipids and protein, if either of those are especially high, that can artificially say that the sodium is low, but really this doesn't have anything to do with osmolality or concentration or physiology. This just has to do with the way that the blood tests are processed and it just kind of throws it off.
 

And this is also the case in jaundiced patients. And I believe it has to do with the way that the cholesterol is processed in a dysfunctional liver. So step one, hyponatremia, is it truly low, or is it related to glucose or protein or cholesterol? The second thing to think about is how low is it? And so this is the same thing as those other labs. And this is all about safety. So the normal range of sodium is 135 to 145 millimoles per liter. And that depends on your laboratory. Mine is a little bit higher, but the magic number to think about in terms of low sodium is 130. So if it's less than 130 and or they have symptoms, they need to go to the ER for at the very least or recheck if not admission for monitoring and treatment.
 

So just to recap of the symptoms associated with low sodium, they're a little bit non-specific, but there they have to do with the kind of side effects of low sodium, which is ultimately brain swelling. So you're going to get a headache, fatigue, lethargy, nausea, vomiting, dizziness, gait disturbances, fatigue, confusion, muscle cramps. So again, a little bit vague, but those are the early signs. And a note here is that typically you will not get symptoms unless it's 129 or less. And also the same thing with the other labs I've already talked about is that acute rises or acute lowering of your blood tests are going to give you more symptoms. So if you're acutely lowering, your sodium you're more likely to have symptoms. And just a quick pause here to talk about the severe symptoms of low sodium. And you're really not going to see this in primary care.
 

So the severe signs of low sodium are seizures, coma, respiratory arrest. And if you're going to see any of those things in primary care, you're going to call the ER, you're going to call the ambulance rather to bring them to the ER. But I use this in counseling patients that are reluctant to take the advice that I'm giving in terms of, "I recommend you go to the ER et cetera, et cetera." It kind of spells it out for them. "Here's where we're going if we're not going to be addressing this." So step one, recapping again, is it really high or is it related to the glucose and protein and cholesterol? Oh, I'm sorry. That's an error. So that should say is it truly low, and I meant to fix that. So is it truly low? How low is it?
 

Is it 130 or less? And do they have symptoms? And then the three kind of categories of diagnosis. I've already introduced this to you, but I'm going to say this... Just re-introduce it again. Because it's a little bit of a tough topic. So this is related to number one, how the kidneys are working at baseline, their normal functioning and what is their status?

Number two intake of salt and water. And number three is that antidiuretic hormone, whether it's working or not. So what's next? So for Jim, it's safe for him to do an outpatient workup because it's greater than 130 on his first check of the sodium, he's asymptomatic. Again, it was like that 134. He doesn't have any symptoms. And this is the low sodium precautions that you can generally recommend to patients with low sodium and it's to limit your water intake and increase the salt intake.
 

And that is a really case-by-case dependent, but that is the kind of broad brush general intervention. And I'm going to get more into that as I progress in the slides. So it's really not assault problem. It's a water problem. So you're going to want to lower the amount of water in their bodies and increasing amount of salt so that the concentration returns back to normal. So quick medication check after you've looked at is it artifact and if it's safe to do so, is it greater than 130, you're going to do a quick medication check. For thiazide, diuretics are the number one medication and he is taking chlorthalidone. But I'm going to take a pause on his management for just a second. SSRI is the antidepressants, antiseizure medications, sulfonylureas the diabetic class, opioids and MDMA, which is ecstasy and hopefully you've gotten that in your social history, what kind of drugs they're using or not.
 

So after that, you're going to get to work on identifying the underlying cause. Because you're going to treat the low sodium. But the most important thing is identifying what's causing it because when you treat that, that's what's going to make it better. So tapping into those three different categories of ways of thinking about low sodium, the first one is kidney function and the status. And this is just a basic physiologic kind of like highlight to take away from this presentation is that there is a set rate of how your kidney makes urine. And then there's the absolute lowest concentration, the most concentrated it can be. And then there's the most dilute it can be. So if you're chugging a ton of water, there is no way that anybody's kidney is going to put out straight water because it's always going to need some sort of solute.
 

And knowing that those are the roles of the kidney, that kind of helps you understand the different things that can... The kidney can only do so much. And so we have to work within understanding that physiology. So do not memorize this, but the average person can make 18 liters of urine per day and about one and a half to two liters per hour. So you can imagine it would be very hard to drink 18 liters in a day, but you can see how people hood feasibly drank more than two liters per hour if they were chugging water for a sport, or they were undergoing like a hazing ritual or another reason I'm going to get to in a second. But you can easily see how the body would drop its sodium because it couldn't keep up with putting out that much water and again, not peeing.
 

So if they have end-stage renal disease and their kidney is not making the concentrated or dilute urine as it should normally, it's just going to make a lot less. And it's going to have a harder time keeping up with that water intake and putting it out appropriately. And again, I just talked about this, but if you're taking in too much fluid, I'm going to get into more on the next slide you can easily overwhelm your kidneys, such that if you drink a ton of water, you're never going to pee straight water. And then you're going to progressively get more and more water in that vessel that is your body and your sodium will drop.
 

So dietary intake of water and salt. So these are kind of fun names, a beer potomania, tea & toast, I think it's syndrome. Primary polydypsia. So beer potomania and tea & toast. The same physiologic things happening is that the diet is majority carbohydrates in the form of alcohol, toast, and then just the tea. It's carbohydrates and water. And when you break down the carbohydrates, it gets metabolized into carbon dioxide, which you breathe off and then water. And so basically you're just chugging water all day long. And so, like I just said, if you're overwhelming your kidneys capacity to get rid of water, your sodium is going to drop because you're going to get fluid overloaded.
 

And the same thing with primary polydipsia, which is refers to people who in mental illness realm of somebody who is compelled to drink too much water or in like a hazing ritual, or like a intensive marathon sport where they're drinking too much water that doesn't have any solute in it. They're going to get overwhelmed with too much water and not enough solute to exceed the maximum dilution of your urine. And again, it exceeds the speed of the kidney to keep up with the excretion that it needs to keep the sodium normal.
 

So this is the third category, and this is a little bit tricky, but ADH, I'm going to break it down. So AHA, is the antidiuretic hormone, but if you want to think about it as the adds hydration hormone, and I cannot take credit for this phrase, because that comes from Dr. Joel Topf , who actually wrote a book all about electrolytes, which I can link to below this video. I'm digging into myself, I haven't read the whole thing, but really excellent resource. It's a little bit long. But anyway, ADH tells the body to hold onto water.
 

So when states of volume depletion, so GI losses like nausea, or excuse me, vomiting and diarrhea or with blood loss, or something like that, you're baroreceptors Tell your body that your fluid volume is low, which triggers ADH to appropriately turn on which hold onto extra water. But you can see in those cases, if you're just holding on to water, your sodium might drop down. So this is unfortunate. In low perfusion states it's a maladaptive response because what's happening is that in cases of low perfusion. So like in heart failure, like cirrhosis, your vital organs are not getting the appropriate blood flow and what your body thinks is that there's not enough volume, but really what's happening it's perfusion. And so in the case, so again, heart failure and cirrhosis. And so if it's not getting perfused, it thinks it needs more volume and more water.
 

So it's going to pump out ADH. And so when it comes to ADH, the low perfusion takes over the low sodium. So there's two signals coming from your body that, "Hey, the sodium is really low. We should turn off the ADH." If your kidneys or your vital organs are saying, "You know what, I'm not getting enough perfusion." It's going to say, "I don't care if there's low sodium, I'm just going to add more and more ADH because we got to get more fluid and more perfusion to those vital organs. So the kind of third state of ADH is that when ADH is just totally bonkers and it's not working at all for no reason. And so that happens in adrenal insufficiency, some cases of hypothyroidism, and then the SIDH, the syndrome of inappropriate ADH.
 

So the three steps of sodium management. So I already talked about those kind of first pass looks at it, but really conceptually what it comes down to is safety. So, number one, is this safe to treat outpatient? Is it above 130? Are they asymptomatic? Number two, what is causing it and trying to treat those causes because that's ultimately going to fix it. And number three, the general broad brush approach to low sodium is that you're going to hold water and you're going to add salt. And that's very case-by-case dependent, but that's just the general conceptual way to approach it.
 

So this is a little bit ugly, but I'm going to really try to break it down the best I can. So step one, if you have a low sodium result like, so this gentleman is 134, you're going to first look at the glucose. Remember that blood sugar is going to artificially lower the sodium, even though it's normal because of the concentration, lipids protein, because that's going to artificially lower it, even though it's normal.
 

I mean, you're also going to look at the GFR because that's going to give you a clue as to, you know what, the kidney is not working well. So that's why it's not able to filter appropriately. So again, I probably said it like five times, but if it's less than 130 and they're symptomatic, you're going to send them right to the ER. If it's 130 to 135, the first thing you're going to look at aside from those first lab tests, are serum osmolality and then take a peek at the med list, because I'm going to tell you right now that the majority of cases in primary care are really going to stop at this step. It's medication-related or it's glucose related, or if it's artifact related, in my experience in the last four years.
 

So if the serum osmolality, the blood concentration is normal. Again, it's not true hyponatremia, it's an artifact. So you're going to go back, circle back, look at the lipids, the protein you're going to consider an ASCAP. Because if there is a super high amount of protein in their blood, you're going to want to investigate that path further. And an ASCAP is that's your protein electrophoresis, which I talked a little bit about in multiple myeloma, a topic for another time, but don't stop your work up there. You do want to like take that as a clue of high protein is something you need to investigate. But in terms of low sodium, you're done, it's actually fine. It's not actually a low sodium. So if the osmolality, meaning the concentration of the blood is low, meaning it's very dilute. There's too much water. There's not enough salt you're going to order a urine osmolality because that is going to tell you two different paths, how concentrated is the urine.
 

So going back to that physiological thing that I was talking about, there's a minimum concentration and a maximum concentration of the urine that the kidney is capable of doing. And in the case of, for example, going back to the beer potomania, somebody who's only having carbohydrates is getting overloaded with water, if your kidneys are functioning appropriately, your urine is going to be super dilute because your body is doing absolutely the best that it can to get rid of as much water as possible. And it just can't keep up. And so if your osmolarity, your concentration of your urine is basically as straight water as it can possibly be it's not going to be ADH related. It's going to be related to the other things that I talked about, which is the tea & toast, the beer, the drinking way too much water or someone's kidneys are just not working.
 

So if you look at the urine and it's very concentrated, with a high osmolality, it's going to be ADH related. And so I'm going to just pause here for a second, because this is the majority of what you're going to see in primary care. I'm going to make another slide in case you are in kind of a higher acuity setting, like a long-term acute care or internal medicine. And you're kind of doing these workups, but for the vast majority of patients, this is what you're going to see. And so I'm going to do a timestamp at the top right of the video with a little I, exclamation point. I think that's what it is. It's going to say the timestamp and also in the comments below that we'll have the timestamp where you can fast forward to. So this is the next step.
 

So if you think that if it's ADH related, there are kind of two general buckets, which I kind of already talked about. So in cases of volume depletion, or lack of perfusion, your body is turning on ADH to hold onto water, to either replace the volume or to try to increase perfusion in the case of CHF and cirrhosis, or there's that syndrome of SIDH, which is just it's just totally bonkers or those extra ones that I mentioned with the adrenal problems and the thyroid problems.
 

So the big takeaway I want you to make, if you're going down this path of working up ADH is your physical exam. Because do not confuse heart failure with volume depletion because those treatments are very, very different. And so if you're in a setting where you're going to be giving IV fluid, or you're investigating that as an option, your physical exam is going to tell you if this is a volume depletion state, or if it's a heart failure state. And it's just a maladaptive ADH secretion, that's like trying to make it better, increase the perfusion.
 

So that's going to come from your... The most accurate, I believe is orthostatic vital signs combined with your laboratory results, which just kind of giving you some information. The physical exams, the dry mucous membranes, the cracked tongue and all that stuff. You can absolutely assess that as well. Oh and sorry. JVD and a pedal edema. You definitely want to look at that in terms of the volume status. Those are absolutely things you want to look at, and in terms of the dry mucus membranes and axillary sweat and all that stuff, not exactly evidence-based, but you're definitely looking for somebody that's fluid overloaded with an edema and pulmonary edema, things like that. And then this is just a kind of a next step, and I'm not even going to get into the full picture of how you go beyond with us.
 

This is kind of like leading you down. So if you, and sorry, this is out of order, but what you're going to order is a uric acid and a urine sodium. I'm not going to talk about the urine sodium. I'm only going to talk about the uric acid for the purpose of this presentation, is that if you have a uric acid and it's low, it's going to tell you that it's CHF or a volume depletion status, which again is differentiated by your physical exam versus if it's a high uric acid, it's more likely to be SADH. So that's like just like a... I don't know, that's a lot of information that I've thrown at you and you can come back and reference this if you need to. But hopefully this has kind of led you down the path in the right direction. And then hopefully you either are in a higher acuity setting or you're sending them to a higher acuity setting, or you have the supervision to kind of help you from here.
 

Okay. So if you're just coming back, if you skipped ahead, this is the management for Jim, and I'm going to pull up his lab tests again, just to review. So what the step one of what we're going to do. We're going all the way back to the initial steps. We're going to look at his other labs. Well, first we're going to see if it's less than 130, and it's not, again, it's 134. We're going to look at the other labs. So again, just repetition for benefit of learning is glucose is normal, creatinine BUN, GFR normal. And then referencing before his lipids were fine and his protein was also fine. So step two is we're going to reconcile his meds. An easy, easy win here is that he's on a thiazide diuretic, which isn't the number one medication that can cause low sodium. And then also his lifestyle factor.
 

So he's drinking a ton of beer and he's not really kind of taking care of himself in terms of other diet. He might not necessarily be amenable to any lifestyle changes, but we can definitely change the medications and have a conversation with him about, something to think about in terms of how can you eat more in your diet if you're not willing to cut down on your alcohol, things like that. So for him, I stopped his chlorthalidone, which was at 50 milligrams, which is actually max dose for a chlorthalidone. But I changed him to lisinopril 10 milligrams because it was changing classes, he's older. I want to make sure that I don't drop his blood pressure too much, even though it's not like a max dose of lisinopril, it's kind of like a mid range, lower dose. And then another thing to think about is that his potassium is low and I made the clinical judgment, decision to not replace the potassium and just change him over to lisinopril because I know the chlorthalidone gets rid of potassium and then lisinopril also raises potassium.
 

And I consulted with one of my colleagues to confirm that that was something that they would choose to do well. And they agreed with that plan, because I didn't want to overshoot it, I didn't want to overdo it. And then I rechecked his labs in a couple of days. I don't think that there's necessarily like a hard and fast one week or three days in terms of like the replacement and the fixing. And I can look into that and see if there's anything that's more concrete. But a couple of days to a week is appropriate. So I'm going to actually just hop back to George. I talked about him like about, I think two presentations ago, and he had the high potassium and the high glucose. And so... Oops, sorry. I meant to say first, his sodium was 126. So again, the magic number is 130, so that's a little scary.
 

But if you do the sodium glucose correction would that five 72 is sodium was actually fine. So that's not something to be too worried about. And then the other thing to keep in mind in terms of this guy's low sodium, is that his GFR, not able to filter as well, as fast. And so something to keep in mind, if he has persistent low sodium, we talk a little bit more about that kind of management. So it's just an FYI for fun. Because I didn't mention that the last time, even that sodium is kind of disturbingly low without that sodium correction. So this is just a recap of his management. So Jim, we rechecked his labs. I rechecked his labs and it normalized his potassium and his sodium. If you remember back to one of the first slides, his TSH was abnormal and he ordered a total T3 and a free T4 to evaluate for hypothyroidism in this case because his labs normalized.
 

It's something to keep in my mind because a hypothyroid can cause low sodium, but not something to worry about right now. I'm just going to investigate that in its own right. If that's something that we should treat or monitor. I also added folic acid and thiamine for him. And I kind of forgot to do this for a long time in my practice and kind of needed reminders. I don't know why it's so hard to remember, but in terms of the protection from Wernicke's encephalopathy, we had a discussion about that. And even though he was not interested in taking medications, I think that he acknowledged his memory wasn't super great. And he was worried about that and he was willing to do that. So I symptoms as prescriptions for him. So in terms of follow-up, I did a nurse visit in one to two weeks to follow up, to check his blood pressure, see how he's doing, any side effects.
 

I made sure that lisinopril is adequately controlling his blood pressure. And then I did a three-month followup with me because I wanted to get buy in with him and I wanted... It's up to you. If you wanted to see him in a month, in two months, in three months, that's really up to your clinical judgment. But I felt like I was very lucky to get him in to the visit and I got his buy-in and we did some new things that he wasn't really planning on doing before. So I was okay with doing the three months and I felt like his blood pressure probably wouldn't change that much. Additionally, we also had that nurse visit to kind of be a cushion in terms of like, is his blood pressure controlled? Okay. Let's just continue our conversation in a couple of months. And then again, if we go back the very first slides, his blood pressure was 144, I believe, systolic.
 

And that's above guidelines. So the new guidelines, depending on the organization that you're referring to are either less than 140 over 90 or less than 130 over 80. I left it at that because this was the first time meeting him. He already told me he was not that interested in doing healthcare things and things that doctors advised him. And so it was not an alarmingly high blood pressure. I got buy in, I built rapport. And the next time I check in with him, especially after that nurse visit, I'm going to kind of see how that's working for him and make sure that that's really the most adequate treatment for his high blood pressure without throwing too much at him at once. Because in my experience, I found that when I try to do everything all at once for patients, they get super overwhelmed and they either ghost me and don't come back or they don't remember anything or they just don't do it.
 

So that's it. I'd love to hear from you. What is your number one takeaway from hyponatremia after watching this presentation? Maybe it's the looking at the glucose and the GFR. Since I did say that probably 1,000 times, but yeah, definitely leave me a comment, I love to hear from you.
 

Did you like this video? If so, hit like and subscribe and share with your NP friends so together we can reach as many new grads as possible to make their first year, a little bit easier. And don't forget to sign up for the email list over at realworldnp.com. You'll get the ultimate resource guide for the new NP. If you haven't gotten it already, but you'll also get these videos sent straight to your inbox with little notes from me, patient stories, more tips and insights and bonus content that I just don't share anywhere else. Thank you so much for watching. Hang in there and I'll see you soon.