Blood Urea Nitrogen (BUN) Lab Values

In this lesson, we’re going to talk about blood urea nitrogen, or BUN.

When we talk about BUN or blood urea nitrogen, we're looking at a lab that's primarily directed at the kidneys. The normal value for bun is 7 to 20 mg/dL.

Let's talk about how we get this value.

So as we eat food, we take in different types of protein and that protein is broken down into amino acids. During this process, the amino acids are broken down further and we're left with ammonia. This ammonia is then transported to the liver, and it's converted to a waste product known as urea. That urea is then kicked out to the kidneys and excreted in urine.

So what happens if the kidneys aren't working? Well that means that urea is not going to be excreted, and it's going to build up in the blood. That's going to be detectable with the blood urea nitrogen, or the b u n test.

So let's recap on the patho. We take in protein, it's broken down into amino acids, and converted to ammonia. Ammonia then converts to urea in the liver, and is excreted by the kidneys. If there's a problem with the kidneys, urea builds up in the blood, and can become an indicator for kidney problems.

When we send this lab off, we're going to send it in a green top tube, and it's going to be commonly submitted with other panels, because we want to look at snapshots of our patient. So this is going to be something like a chem 7, or BMP, it could be sent in renal panels, or it could be sent in the comprehensive metabolic panel, and that's going to give us more in-depth information.

Let's say we get our labs back, and the BUN in is abnormal, what does that mean?

If it elevated, we want to look to see if the kidneys are working properly. If they're not, you're going to get this elevation of the bun, because they can't be excreted it in the urine. Also if your patient’s dehydrated, that can cause slight increases in BUN. Other reasons for BUN elevation are going to be congestive heart failure, myocardial infarction, diabetes, and even a urinary obstruction.

If it's decreased, we need to look at other reasons why it's low. This could be due to liver failure because of the inability to convert ammonia to urea. If you have patients that are overhydrated, there BUN can go down as well. If you're not getting adequate protein in their diet, that could be a cause for decreased BUN and also pregnancy can affect your patient’s BUN levels.

So this lesson on BUN we really focused on those nursing concepts of lab values in elimination, because BUN is really associated with the kidneys.

Let's recap.

Normal values for BUN are 7 to 20 milligrams per deciliter.

BUN focuses on primarily the kidneys, but we can also have some other issues going on.

If you have an increased BUN, that could indicate a problem with the kidneys, but you can also look at things like a dehydration or heart dysfunction.

If you're BUN is decreased, look at causes for why there's no urea production, and that would be primarily in the liver or even over-hydration.

BUN is considered an essential rental value, meaning that this life is going to be included in almost every kidney panel.

That’s it for this lesson on BUN. 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!!