02.06 Phosphorus-Phos

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Hypocalcemia – Definition, Signs and Symptoms (Mnemonic)
Hypercalcemia – Signs and Symptoms (Mnemonic)
Nursing Lab Value Skeleton (Cheat Sheet)
Electrolyte Abnormalities (Cheat Sheet)
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Lab Value Match Worksheet (Cheat Sheet)
Shorthand Labs Worksheet (Cheat Sheet)
Fluid and Electrolytes (Cheat Sheet)
63 Must Know Lab Values (Book)
Phosphorus (PO43-) Lab Value (Picmonic)

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In this lesson we’re going to talk about Phosphorus. We’ll look at what it does in the body and what happens when it’s too low or too high.

First, the normal range for Phosphorus is 3.0 - 4.5 mg/dL. If you’re using the labs shorthand, you’ll see it here in this spot. Now, in my opinion, phosphorus doesn’t get ENOUGH attention. The truth is that we don’t see abnormalities in phos very often, but when we do, it can cause a lot of problems because it has a HUGE role in our system. It’s responsible for cellular metabolism and energy production. Remember ATP is our energy source - it stands for Adenosine Triphosphate. That means Adenosine plus THREE phosphates (which is just another form of phosphorus). We also see it in the phospholipid bilayer of our cell membranes. Remember this from A&P - we have these phospholipids, which is a phosphorus and some lipids or fats, and there are two rows of them like this. You may have some protein channels in here. And this makes up the cell membrane. So if we don’t have enough phosphorus, we can’t have good solid cell membranes. It also helps to keep our bones and teeth strong and it has an INVERSE relationship with Calcium. So if Calcium goes up, Phosphorus goes down and vice versa.

So, again, we’re going to look at what happens when it’s too low and too high. Let’s start with hypophosphatemia or low phosphorus - less than 3.0 mg/dL. The most common causes of hypophosphatemia are alcohol abuse, renal failure, and malnutrition or starvation. Specifically - what we see in this case is that when a patient has been starved or malnourished for so long and then suddenly we start feeding them, or giving them TPN, Total Parenteral Nutrition, they can develop what’s called Refeeding Syndrome. Essentially this is where their body responds excessively to the extra nutrition and starts shifting fluid and electrolytes around like crazy, causing a lot of imbalances, with the classic one being hypophosphatemia. So definitely something to look out for and be aware of. Make sure you’re working closely with your dietician when you start feeding patients. You can also check out our nutrition lessons in the Fundamentals course to learn more. We may also see this with hyperparathyroidism because of the relationship with calcium. Hyperparathyroidism means hypercalcemia, which means hypophosphatemia.

When we look at symptoms of hypophosphatemia - make sure you remember phosphorus’s role in the body. So the symptoms are generally related to not having enough energy (or ATP) and having damage to those cell membranes. Cardiovascularly we see a decreased cardiac output and stroke volume and weak pulses because of the lack of energy available for good contraction. We’ll see muscle weakness because of the lack of energy and possible rhabdomyolysis because of the breakdown of the cell membranes. When that happens, we see muscle cell damage - which is what can cause Rhabdo. We could see the density of our bones decrease and increase the risk of fractures, and we could see CNS irritation - again because of these issues with ATP and cell membrane damage.

Best thing we can do is replace the phos, usually IV, and always slowly. If you watch any of our other electrolyte lessons, you’ll see that they all need to be replaced slowly because if we replace too quickly we can cause more problems. Of course we also want to treat the underlying cause and discontinue any meds that are decreasing our phosphorus levels. That might be antacids, calcium supplements, osmotic diuretics, or even phosphate binders. We can also make some dietary changes. Now here’s the big point I want you to remember - if phos is low, calcium is...high, right? So if I want to bring my phos UP, what should I do with my calcium? Decrease it! SO - not only do we want them increasing phosphorus rich foods like beef, chicken, nuts, and fish, BUT we ALSO want them decreasing their calcium intake - so they should avoid dairy and greens as well. So increase phos, decrease calcium.

Now, let’s look at the other end of the spectrum with hyperphosphatemia, which is a level greater than 4.5 mg/dL. This is pretty rare, but the most common causes are going to be hypoparathyroidism - again, due to a low calcium and the inverse relationship - renal failure, and excessive intake (or even overcorrection). We can also see this with something called Tumor Lysis Syndrome. This happens when the body or the chemotherapy is breaking down a tumor and it begins to release toxins and cell byproducts into the bloodstream. Of course as we break down those cancer cells, that includes the cell membrane, which releases phosphorus.

When it comes to symptoms - hyperphosphatemia is typically tolerated pretty well and doesn’t usually produce symptoms on its own. But, since we know it’s often associated with hypocalcemia - those are usually the symptoms we see. Make sure you refer to the calcium lesson for details, but most commonly you’ll see muscle twitching, Chvostek’s and Trousseau’s sign, as well as bradycardia and hypotension.

Our main course of action for hyperphosphatemia is going to be to treat the cause. We can also give phosphate binders like Phos-Lo - it even tells you in the name what it does - Lowers Phos! Big point here is to make sure you give this WITH meals, because the whole point is to bind the phosphorus in the food so it doesn’t get absorbed. And then, of course, we will also treat the hypocalcemia appropriately as well.

Okay, so let’s recap. Normal value of phosphorus is 3.0 - 4.5 mg/dL. It serves to provide us with energy in the form of ATP, helps create the cell membranes, and helps strengthen bones and teeth. And we know that it has an INVERSE relationship with calcium! Common causes of hypophosphatemia are alcohol abuse, malnutrition - specifically issues with refeeding syndrome - and acute renal failure. The symptoms we see are entirely related to the lack of energy and the damage to the cell walls. We need to replace phosphorus and stop any further losses. We most commonly see hyperphosphatemia in hypoparathyroidism and with excessive intake and we see that the symptoms are usually related to the hypocalcemia that goes along with it. We will give phosphate binders and treat the hypocalcemia as well. Our main priorities are going to be to treat the cause and make sure we’re looking at other labs because the patient most likely has something else going on as well.

That’s it for phosphorus, I hope this was helpful. Don’t miss all of our other electrolyte lessons and make sure you check out all the resources attached to this lesson. Now, go out and be your best selves today. And, as always, happy nursing!!
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