Putting an End to Calcium Confusion
So, you’re looking at your BMP and your calcium is low. Are you nervous? It depends. That’s because calcium can be a wee bit confusing due to its propensity to bind itself to albumin…so next you look at your albumin level and then people start throwing around terms like “corrected calcium” and “ionized calcium.” Don’t worry…it’s not as rough as it seems. Here’s the skinny.
About half of calcium is bound to proteins where it doesn’t do much for us physiologically…it just hangs around trying to look cool. The other half of the calcium is “ionized” (remember, ionized calcium refers to the free-flowing calcium that can do all the things calcium is supposed to do…it is also sometimes called “free calcium”…think of it as “free and available” and not “married and unavailable.”)
So, the protein that most of your calcium binds to is albumin (which you should also see on your BMP). If your albumin is low, the amount of calcium bound to it is low…and this will show up as a low calcium on your BMP. So…you get your labs back and you see right away that your calcium is low…the next thing you look at is your albumin…is it also low? Then that’s probably your problem. But remember, we have OCD, so we’re going to correct our calcium just to be sure (and sound super smart in the process). Ready?
Corrected calcium = Total calcium + 0.8(4.0-albumin). So…get out your calculators. If your patient has an albumin level of 2.4, and a total calcium of 7.4, what’s your corrected calcium? Yes, it’s 8.68…which is normal (8.5 to 10 mg/dL is normal for adults).
If you are working in ICU and your patient is on the vent, the ABG will show an ionized calcium, which saves you from having to do a bunch of math in the middle of the night. Note that the values for ionized calcium are different, but why go into that here and muddy the waters? The end result is the same…high is high and low is low…and what are you going to do about it?
Well, you probably remember from your physiology that calcium is super important in the transmission of nerve impulses, contraction of skeletal and cardiac muscle, and regulation of heart rate and blood pressure. Note that both high and low calcium levels can cause cardiac problems (along with a whole host of other issues including laryngospasm with stridor, seizures, and paralytic ileus)…so the goal here is to keep it normal, ya’ll. Basically, a level above 12 mg/dL is life-threatening, as is a level below 7 mg/dL. Scary stuff…but also super interesting!
To correct a low calcium, you’re going to give…..calcium! Some folks will be fine with PO supplementation, but your super sick patient is going to need it corrected NOW! Giving it quickly will cause vasoconstriction of your blood vessels, so don’t be doing that please (unless maybe you’re in a code situation, in which case it will probably be given IVP). Please watch for tissue necrosis with calcium gluconate and calcium chloride…central lines are usually preferred, but that may just be the ICU nurse in me. You’ll also want to correct any concurrent hypomagnasemia since a low mag level can decrease hormone secretion from the parathyroid, which we all know plays a role in calcium levels. So along those lines, you’ll also want try to figure out what’s causing the problem in the first place…is it renal failure, malabsorption, hypoparathyroidism, a low mag level, sepsis? I swear, going to work is like putting on your Sherlock Holmes hat every single day.
So, what if your calcium level is too high? Always always try to figure out what’s causing the high levels and see if you can fix that first. Emergency treatment of an elevated calcium level involves promoting natriuresis (fluids with a loop diuretic such as lasix), IV phosphate in critical situations, IV calcitonin, and yes…more fluids to keep those kidneys kicking out the calcium. All the while, you’ll be watching your patient and the monitor for scary things, just in case.
Ok, so your assignment is to waltz into work or clinical, check out your labs, correct your calcium and feel like a rock star. Or, just a super awesome nurse.
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