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

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


Well hey there it’s Liz Rohr from Real
World NP and you’re watching NP Practice Made Simple, the weekly videos 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 of my four years of primary
care it’s been the first couple of steps will lead you to your etiology
for the low sodium and help you with that workup and plan. So without further
ado, I’m gonna share my screen with you. Alright so here’s the case study on
hyponatremia. So Jim is a 61 year old man, he’s reestablishing care with the 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 medication 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 8 ounces of water or less per day so he’s not you
know 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 and emphysema, alcohol use disorder and
diverticulosis remotely. He’s got no past surgical history or
family history that he knows of. He’s taking chlorothiazide 50mg 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 144/80, 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. I
really appreciated how forthcoming he was and honest. So the plan today I’m
going tofocus on hyponatremia but I’m going to touch on the other components of
holistic care at the end. So to start I’m gonna 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 gonna check a
hemoglobin a1c which is a diabetes screening test according to the USPSTF
guidelines. I’m also gonna check a thyroid function study, a TSH and then I’m
gonna check his lipid panel again in accordance with the USPSTF
screening guidelines according to his age. So here are his lab results. Just
to start, his CBC is normal and his cholesterol and lipids are also normal
which I was pleasantly surprised by. 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 in one slide. The glucose is normal the BUN,
creatinine and GFR and showing normal kidney function. His sodium is low 134, and 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. 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 at the normal range
of 98 – 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 alk phos. So a 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 on to more water then 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 basic way to conceptualize hyponatremia. So it’s
really more about water than it is about salt. I’m going to use the you know
the benefit of repetition because this can be a little bit of a tough topic but
I’m so I’m just gonna introduce the three main reasons we get low
sodium. And this has to do with how the kidneys function just in a 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– just, just to stay with 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 if you saw the last case
presentations that I did on high potassium and high calcium this is also
the first step for those two is to really validate is this actually a lab
test that we can trust as being actually low, or is it artifact? So fun fact, when
you think about sodium after thinking about that first kind of tenet 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 lowers sodium and that has to do with the
concentration of the blood. So when you have a super high glucose level
your sodium is going to go down to compensate for that. 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 it 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 it that the the way that the
cholesterol is processed in a dysfunctional liver. So step one, hyponatremia– it truly low or is it related to glucose or protein or
cholesterol. The second thing to think about is how low is it? 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 mmol/L and that depends on your
laboratory– mine is a little bit higher– if 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 a recheck, if not admission for monitoring and treatment. So just a recap of the
symptoms associated with low sodium they’re a little bit nonspecific but they have to do with the with the side effects of low sodium
which is ultimately brain swelling, so you’re gonna get a headache, fatigue,
lethargy, nausea, vomiting, dizziness, gait disturbances, fatigue, confusion, muscle
cramps, so again a little bit of vague but those are the early signs. And a note
here is that typically you won’t 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. You’re really not going to see this in primary care, I
mean if somebody has the severe signs of low sodium are
seizures, coma, respiratory arrest, and if you’re gonna
see any of those things in primary care you’re gonna call the ER– you’re gonna
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” you know, etc, etc It kind of spells it out for them–
here’s where we’re going if we’re not gonna be addressing this. So step 1
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 it 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 gonna say this– just
reintroduce 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 let’s– 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. And taking
that is a really case-by-case dependent but that is the kind of broad brush
general intervention and I’m gonna get more into that as I progress in the
slides. So, it’s really not a salt problem it’s a water problem and so
you’re going to want to lower the amount of water in their bodies and increasing
of salt so that the concentration returns back to normal. So quick
medication check, after you’ve looked at, you know, is it artifact? and is it safe to
do so, is it less is or greater than 130? You’re going to do a quick medication
check. Thiazide diuretics are the number one medication and he is taking
chlorthalidone, but I’m gonna take a pause on his management for just a second.
SSRIs, the antidepressants, anti-seizure 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 gonna get to work on identifying the underlying cause because
you’re gonna treat the low sodium, but the most important thing is identifying
what’s causing it. Because when you treat that, that’s what’s gonna 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 highlight to take away from this presentation is
that there is a set rate of how your kidney makes urine and then there’s a
an 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
urine– straight water excuse me– because it’s always going to need some sort of
solute. And knowing that is the role of the kidney that
kind of helps you understand the different things that– you know like,
that the kidney can only do so much and so we have to work within that
understanding, that physiology. So, do not memorize this– but the average patient,
average person can make 18 liters of urine per day, and about one one and a
half to two liters per hour. So you can imagine it would be very hard to drink
18 liters a day, but you can see how people could feasibly drink more than 2
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 would drop its sodium because
you 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 gonna 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 gonna, you know,
you’re gonna 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: Beer Potomania, Tea and toast
I think it’s syndrome, primary polydipsia. So, beer potomania and tea and toast–
the same physiologic things happening is that the diet is majority carbohydrates
in the form of alcohol, toast and then just the tea– its 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 gonna get fluid overloaded. And the same thing with primary polydipsia,
which is refers to people who, you know, a 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 gonna 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
to keep the sodium normal. So this is the third category and this is a little bit
tricky but ADH– I’m gonna break it down. So ADH if you 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 I comes from Dr. Joel Topf, who
actually wrote a book all about electrolytes which I can link to
below this video. It’s actually, 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 on to water. So in states of volume depletion,
so GI losses like nausea or –excuse me– vomiting and diarrhea or blood loss or
something like that, your baroreceptors tell your body that your
fluid volume is low, which triggers ADH to appropriately turn on, which holds onto extra water. But in you can see in those cases, if you’re just holding on to
water, your sodium might come and drop down. So this is unfortunate, our
body is trying 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 perfusion 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 this sodium is really low we should turn
off the ADH” if your kidneys or your vital organs are saying, you know, “I’m not
getting enough perfusion” it’s going to say “I don’t care if there’s a low sodium
I’m just gonna add more and more ADH” because we gotta get more fluid and
more perfusion to those vital organs. So the 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 SIADH 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 gonna fix it. Number three the general broad
brush approach to low sodium is that you’re gonna hold water and you’re gonna
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 gonna really
try to break it down the best I can. So step one, if you have a low sodium result– so this gentleman is 134– you’re gonna first look at the glucose. Remember the 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. We’re also gonna
look at the GFR because that’s kind of give you a clue as to, you know, if
the kidneys aren’t working well, so that’s why it’s not able to filter
appropriately. So again, I’ve probably said it like five times [laughs] but if it’s less than 130 and
they’re symptomatic, you’re gonna send them right to the ER. If it’s 130 to 135, the first thing you’re gonna look at aside from those first lab tests are
serum osmolality and then take a peek at them med list because i’m going to tell
you right now, that first, the majority of cases in primary care are
really gonna stop at this step– it’s medication related or its glucose
related or if it’s artifact related in my experience in last four years. So if
the serum osmolality– the blood concentration– is normal, again it’s not
true hyponatremia– it’s an artifact. You’re going to go back circle back look
at the lipids, the protein, you’re going to consider an SPEP because if there is
a super high amount of protein in the blood you’re going to want to
investigate that path further and that SPEP is like that serum protein electrophoresis
which I talked a little bit about and multiple myeloma– 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 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 into 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– and
if their 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. So if your
osmolality– 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 the, you know, 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, it’s a high
osmolarity, it’s going to be a 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 work ups, but the vast majority of patients– this is what you’re
going to see. And so I’m going to do a time stamp at the top right of the video
with a little i or exclamation point I think is what it is that’s going to say
the time stamp and also in the comments below that I’ll have the time stamp
where you can fast-forward to. So this is the next step so if you think that if
it’s AD- related . There are kind of two general buckets which I kind of already
talked about. So in cases a volume depletion or lack of perfusion, your body
is turning on ADH to hold on to water, to either replace the volume or to try to
increase perfusion. In a case of CHF and cirrhosis, or there’s the syndrome of
SIADH which is just, you know, it’s just totally bonkers or those extra ones that
I mentioned with the adrenal problems and hypothyroid
problems. So the big takeaway I want you to make if you’re going down this path
of working of 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 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 gonna come from your– the most accurate I
believe is orthostatic vital signs combined with, you know, your laboratory
results which is giving you some information. The physical exams, you know,
them dry mucous membranes the cracked tongue and all that stuff,
you can absolutely assess that as well and sorry jvd and the pedal edema you
definitely look at that. In terms of the volume status, those are absolutely to
look at but in terms of the the dry mucous membranes, axillary sweat and all
that stuff, like not exactly evidence-based, but you’re definitely
looking for somebody that’s fluid overloaded with edema and, you know,
pulmonary edema, things like that. And then this is just a kind of a next step
and I’m not gonna get into the full picture of how you go beyond with this–
this is kind of like leading you down so if you– and sorry this is out of order–
but what you’re gonna order is a uric acid, and a urine sodium. I’m not gonna
talk about the urine sodium, only the uric acid for the purpose
of this presentation– if you have a uric acid and it’s low, it’s gonna tell
you that it’s CHF or a volume depletion status, which again is differentiate by
your physical exam. Versus, if it’s a high uric acid, it’s more likely to be SIADH.
so that’s like just like— 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 is kind of led you down the path in the right direction. And then
hopefully you’re either 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 gonna pull up his lab test again just to review. So
the step 1 is what we’re gonna do we’re going all the way back to the
initial steps. We’re gonna look at his other labs. Well first we’re gonna see if
it’s less than 130, and it’s not, again its 134. We’re gonna look at the other
labs, and again just repetition for benefit of learning–his glucose is normal,
creatinine, BUN, GFR normal and then you know, referencing before his lipids were
fine and his protein was also fine. So step 2 is we’re gonna reconcile his meds. An easy easy, easy win here is if he’s on a thiazide diuretic, which is the
number one medication that can cause low sodium.
And then also his lifestyle factors– so he’s drinking a ton of beer and he’s not
really kind of taking care of himself in terms of adequate 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, you know, something I 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 chlorthalidone
but I changed him to lisinopril 10mg 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 the max dose of lisinopril– it’s kinda 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, you know, confirm that that was
something that they would choose to do as well and they agreed with that plan.
Because I don’t want to overshoot it and 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, you know, one week or three days in terms of like their 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 gonna 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 it’s a little scary right? But if you do the sodium-glucose correction
with that 572, his sodium is actually fine, so that’s that’s not something to
be too too worried about. Another 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 you talk a little bit
more about that kind of management. That’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– the potassium and
his sodium. If you remember back to the first one,
of the first slide says TSH was abnormal, and I ordered a total t3 and a free t4
to evaluate her hypothyroidism. In this case because his labs normalized, it’s
something to keep in my mind because of hypothyroid can cause low sodium, but not
something to worry about right now. I’m just gonna 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
sent them 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 and make sure the lisinopril is adequately
controlling his blood pressure. I did a three-month follow-up with me because,
you know, I wanted to get buy-in with him and I wanted, you know, it’s up to you if
you wanted to see him in a month, in two months, or 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 his blood
pressure control. And just continue our conversation in a couple
months. And then again if we go back to the very first slides, his blood pressure
was 144 I believe systolic and that’s above guidelines with the new guidelines
depending on the organization that you’re referring to– either less than
140 over 90 or less than 130 over 80. I left it at that because this is the
first time meeting him, he already told me he was not that interested in you
know, 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 the
most adequate treatment for his high blood pressure without throwing too much
at him at once. Because I– in my experience,
when I try to do everything all at once for patients, they get super overwhelmed
and either ghost me or 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 a thousand times, but yeah definitely leave me a comment I love to
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