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Interpreting Urine Culture and Sensitivity Tests (Nursing)

by Rhonda Lawes

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    00:00 Hi, welcome to our video series on interpreting lab values. On this one, I'm going to teach you how to interpret urine culture and sensitivity lab tests. Now, effective antibiotic treatment plans are critically important to the safety of your patient. The urine C&S lab test is one of the most critical tools in identifying a UTI and in working together as a team to make sure the treatment plan is effective. Results from a C&S can take a while to come back. Usually it's 1 to 2 days, but it can take up to 3 days to be received from the lab. So we can start empiric antibiotic therapy. Now, if you'll underline that word empiric, that means it's an educated guess based on what we know about our community. Even though we haven't identified the organism, we have a pretty good idea of what's commonly found in our community so we know which antibiotics we could start. We usually start with a broad-spectrum antibiotic and we'll try to get that much narrower as we get the results back. So empiric antibiotic therapy can start initially until the C&S results are received. Now, looking at the results of the C&S are within the parameters and the practice of multiple disciplines. So this isn't just something the physician does. It's things the whole team do to work together to keep your patient safe. So this is within the scope of practice of physicians, nurses, and PharmDs. You may know them as pharmacists but because they get a doctorate in their specialty, you'll also hear them referred to as PharmDs. Now take a look at the culture and sensitivity report. That's another one of those forms that is just overwhelming, but don't worry we're going to break it down.

    01:50 The top part is the culture information. The bottom part is the sensitivity information. Now this is just an example of what you might see in a hospital setting. Every lab is going to report it a little bit differently, but the format is going to be essentially the same. So we're going to dig down deep in the culture report section. Now remember, the number of colony-forming units per mL is an estimate of the number of bacteria in the sample. So if you're not familiar with that, make sure you write yourself a note. CFU stands for colony-forming units and it helps us estimate the number of bacteria in the sample. Now I want to draw your attention to the 24-hour results and organism 1. Now look at 24-hour results. See what it says there? Growth, good. That means something grew. So, after 24 hours, a bug grew and it was identified as organism #1 with a name of Escherichia coli, that's E. coli. Now look at the colony count there. Can you see it? 10 to the 5th power. Good job. I promised reading a culture report is actually this straightforward. Was there growth, yes or no? Here it says yes because we have the word growth. Which organism is it? Well, organism #1 because sometimes your patient has multiple organisms, but organism 1 is E. coli with CFUs of 10 to the 5th power. So, 3 or 5, maybe you're confused. You've seen this report at different places. Some say 10 to the 3rd power, some say 10 to the 5th power. Many labs define 10 to the 5th power CFUs per mL urine as the minimum threshold. But here's the deal, other people would argue that this higher threshold misses many relevant infections. So, they are there for other recommendations that recommend a diagnosis of a UTI from a count of 10 to the 3rd power CFUs per mL. So if you see it that way in literature, that's the reason there's that comparison. So depending on the types of bacteria that are detected, 10 to the 3rd power might be indicative of a UTI or 10 to the 5th power might be the indication of a UTI. While we're at it, let's talk a little bit about math. What is 10 to the 5th power? We saw there that organism 1 is E. coli and the CFUs were 10 to the 5th power. That's actually 100,000 because it's 10 to the 5th power. That's 1 plus 5 zeros. It's 10 x 10 x 10 x 10 x 10. Right? You do that, multiply 10 five times. That's just a shorthand way of writing it. When we say 10 to the 5th power, that's what we mean, 1 plus 5 zeros or 10 x 10 x 10 x 10 x 10. Now if you remember that from math, rock on. Just celebrate what you already know and you're carrying forward. The first culture report we looked at had 1 organism. Take a look at this culture report. Right, what's different? There are 2 organisms. Now, look at the CFU count. Organism 1 is 10 to the 3rd power. Organism 2 is 10 to the 4th power. So know that when you're looking at culture and sensitivity reports, details matter. So pay attention to how many organisms you have and take a look at that CFU for your reference. Now we've broken down the culture part of the report, we're going to take the next step and that's looking at how to interpret the sensitivity table. Now I've got an example of a sensitivity table there for you to take a look at. You can see there are several drugs listed and a lot of numbers. Let's break that down. First, let's look at the list of antibiotic medications. See on the left, it starts with amikacin, ampicillin, all the way down there in alphabetical order. Next, I want you to look at the organisms. Now you've got numbers less than or equal to, greater than or equal to. I don't want you to pay attention to the numbers. What I'm going to ask you to pay attention to are the letters. Now, look when we've talked about seconds, it's a small "s" but see here you have a capital "S". That stands for sensitive. A capital "R" means resistant. That means the bug is resistant to a drug if you see an "R" by it. It is sensitive or that's an effective medication if there's an "S" by it. So take a look at our list. What I want you to do is draw a line through the drugs the bug is resistant to, okay. How many do you see? So, take a minute, we're into the entire list of the drugs, and draw a line through the drugs the bug is resistant to. Okay, once you've done that you can see there's just one. Right? Ampicillin is the only drug that has an "R" under organism 1. Cool, so we know for sure we don't want this patient to be on ampicillin because it is not going to be effective.


    About the Lecture

    The lecture Interpreting Urine Culture and Sensitivity Tests (Nursing) by Rhonda Lawes is from the course Interpretation of Renal Lab Values (Nursing).


    Author of lecture Interpreting Urine Culture and Sensitivity Tests (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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