# BUN-to-Creatinine Ratio (Nursing)

by Prof. Lawes

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00:00 Now just like the name says the BUN to creatinine ratio is an actual formula.

00:06 BUN the blood urea nitrogen goes on the top serum creatinine goes on the bottom.

00:12 Now, I'm going to tell you what happened to my Aunt Crystal.

00:15 She was in the ICU at the very same time I was creating this presentation for you and my cousin was texting me lab values and my eyes were as big as saucers.

00:25 Luckily. She's doing great.

00:27 She's back home, but for a while there it was not looking positive for her.

00:33 Okay, so let's do the math.

00:34 73/4.010 mg/dL What do we get? This was going to be outrageous because my aunt was so sick.

00:44 Wait a minute the numbers 18.20 well what's considered normal.

00:51 12 to 20.

00:53 Well while my aunt had a lot of things going on the reason she went to the hospital was for severe dehydration.

01:01 So even though these numbers look abysmal, It was still was within the normal range for BUN to creatinine ratio.

01:08 BUN wasn't normal, serum creatinine wasn't normal, but she was still within the normal range for a BUN to creatinine ratio.

01:17 So what does this BUN to creatinine ratio tell us that a simple creatinine or BUN can't.

01:24 Well it can help us determine if the cause of the elevated BUN that high urea or creatinine is a renal or non-renal cause.

01:33 Now I don't want to buzz through that because this is something we use in practice and it's something you need to be aware of.

01:39 The math is simple but understanding what it represents is really important because of BUN to creatinine ratio can help us recognize if the problem is renal or non renal.

01:53 In this case, It wasn't my aunt's kidneys that were the problem.

01:57 The problem was they had a pre renal issue.

02:00 Were not getting enough blood supply.

02:02 She was in acute kidney injury, they replace the fluids and her kidneys perked right back up and she did fine and was discharged home.

02:11 So why you want to know what the BUN and creatinine ratio is is it can help you determine through very simple math if the cause is renal or non-renal.

02:22 Now let me give you a quick chart.

02:24 You see in the left-hand column you have greater than 20, greater than 12 to 20 or less than 12, so greater than 20 s going to be a pre rental problem.

02:34 You can see that she was on her way if she wouldn't have gotten help, if she wouldn't have gone to the hospital.

02:39 She definitely would have kept right on going up past 20.

02:43 So when you get a value like this you want to watch for signs of hypoperfusion of the kidneys, my aunt was hypo perfused.

02:50 She was so intravascularly dehydrated her kidneys were not receiving an adequate blood supply.

02:56 You'll also want to check for things like excessive protein or GI bleeding, remember those red blood cells have hemoglobin which is a protein that can also cause an increase in the ratio.

03:07 Now if it's 12 to 20, that is within the normal range, but there might be a post renal problem some type of obstruction.

03:14 Less than 12, that's not a good sign.

03:18 That's an intrarenal problem.

03:20 Now, it may also indicate liver disease or malnutrition there just may not be hardly any protein available to the patient because they're either malnourished.

03:30 They're not eating or the liver can't process protein like we depend on it doing.

03:35 So you want to keep in mind if you're taking care of a patient most patients have a BUN and a creatinine you can look at that BUN to creatinine ratio and line it up with the rest of the assessment you see with your patient.

03:48 So that was the basics of the BUN to creatinine ratio, but I want to point out a couple of other categories to keep an eye on.

03:55 If your patient is elderly they may have an elevated BUN to creatinine ratio as a baseline, meaning they have that before they came into you because as we age you have a decreased muscle mass.

04:07 So keep that in mind, the out early usually are a special case.

04:11 We're dealing with medications and lab work and this one is no exception.

04:15 So you're elderly patients may have an elevated BUN to creatinine ratio normally as a baseline.

04:22 So keep an eye on your Trends.

04:24 Now the next one you can have other reasons for having a disproportionate rise in BUN relative to creatinine, so that's what we're talking about.

04:33 Why do we have such a higher BUN than we do the creatinine what can be caused by hyper catabolic states, high-dose glucocorticoids, and the reabsorption of large hematomas.

04:45 I want you to kind of think of that just for a minute, hyper catabolic states your body for whatever reason is under extreme stress and is just ripping through your cells.

04:57 High-dose glucocorticoids mess with everything, right? Protein, fat, metabolism, blood sugars, they can wreak havoc on a body.

05:05 When we say high dose glucocorticoids, this isn't what somebody's taking in an inhaler for their asthma.

05:13 This is high-dose steroids probably given orally or IV.

05:19 The last one reabsorption of large hematomas.

05:22 Remember that's blood cells being reabsorbed back into the body and that's going to be a source of high protein.

05:29 So those our special notes to consider when you're evaluating a patient's BUN to creatinine ratio.

05:35 Watch out for the elderly.

05:37 You can expect a change there.

05:39 Hyper catabolic states, high-dose glucocorticoids and the reabsorption of a really large hematoma.

The lecture BUN-to-Creatinine Ratio (Nursing) by Prof. Lawes is from the course Serum Creatinine – Renal Assessment (Nursing).

### Included Quiz Questions

1. To determine whether the cause is renal or nonrenal
2. To identify the amount of urine the kidneys filter per minute
3. To find out the extent of nephron damage
4. To determine whether it is acute or chronic kidney injury
1. Liver disease
2. Excessive protein intake
3. Severe dehydration
4. Diabetes
5. Malnutrition

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