Creatinine Clearance Lab Values

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Hey everyone. My name is Abby here with and this lesson, we're going to talk about creatinine clearance. We'll talk about both blood and urine. We'll talk about what the normal values mean, their relationship to each other, as well as what might cause it to be increased or decreased. Let's dive in! 


Creatinine clearance, abbreviated CrCl, is a test that compares, that's a big part of this lesson, it compares the level of creatinine in the blood against that that is in the urine, and the biggest thing that we're here to talk about is the estimated GFR or glomerular, which is so hard for me to say, filtration rate. If you look at this image, I think it's so cool, and I'm super proud of myself for finding it, this is an up close view of the glomeruli. This is the little fenestration, the little pockets that actually contribute to the filtration of solutes and fluid inside Bowman's capsule. That eGFR is the amount of blood that's filtered per minute through the glomeruli. Factors that impact the GFR are hydration, blood volume status, and blood pressure. Creatinine, which is what we're measuring in both the blood and the urine, is a byproduct of muscular energy expenditure. So, it's normal to have some in the blood and some in the urine. Some times when we would measure this are to monitor or evaluate kidney function. Now GFR is an estimation, so it's not the strongest way that we can look at kidney function, but it's definitely a good thing to look at. Uh, of course, some things that are going to affect the, uh, GFR, are diabetes, remember how irritating those blood sugar crystals can be, uh, in the, in the blood and for those tiny, tiny little vessels in the glomeruli, heart failure, because we're not getting enough perfusion to the kidney,  

so therefore we're going to have a decreased GFR, and then hypertension. This picture is actually a picture of a gentleman's glomeruli and showing the damage to the glomeruli because of a hypertensive crisis. 


Normal therapeutic values are between 97 and 137 milliliters per minute in men, and in women 88 to 128. But keep in mind, creatinine clearance actually slows with age, that's a normal thing. So, for every decade after age 40, a normal test result is going to be about 6.5 milliliters, less than these numbers here above. Collection is in a plasma separator tube when we're evaluating the blood portion of this test, and urine is a 24 hour collection. Now, if you remember a 24 hour collection, it's in that brown or red plastic container, and the first void is actually flushed. The date and time is recorded for each void afterward, and the urine is collected and stored at room temperature. It is all processed once the collection of the urine is complete and it gives a full blown, 24 hour view of how much of that creatinine is actually present in the urine, and it should be very quickly thereafter, that we get our blood sample. 


The kidneys are solely responsible for removing creatinine from the blood, so we know if kidney function is declining or abnormal, that's going to decrease the GFR, because it's not filtering properly right? And so, to anything that has to do with hypoperfusion, so anything that causes less blood to flow through, uh, the kidney as well, will reduce our GFR, such as congestive heart failure, and even poorly-controlled hypertension, because of the damage that it does to the glomerulus, and of course, because the heart isn't moving blood forward like it should in CHF. Dehydration is another cause, as well as an obstruction in the bladder, and nephrotoxic medications. I saw this often in my patients that I gave chemo to. Sometimes, their creatinine clearance was so low, we couldn't do treatment. It will be increased if the glomerular filtration rate is higher, and that can happen due to a higher blood volume like in those that are pregnant, someone that has a large protein intake, because the byproduct of protein is creatinine, and then also, strenuous exercise. Your muscles release that creatinine. That's why it's normal to have a little bit in the urine and a little bit in the blood. And if you have strenuous exercise to the point of injury, you could have an increase, um, in your creatinine clearance. 


Now, our linchpins for this lesson are that the creatinine clearance is a lab to measure and compare creatinine concentration in the urine and the blood. Its main use is to evaluate glomerular filtration rate. In males, 97 to 137 milliliters per minute is normal, whereas in females, 88 to 128 is normal. Now, kidney function does change with age, so every decade after the age of 40, a normal test result will actually be 6.5 milliliters per minute less than these values here. Now, we talked about increased values. We can see that in pregnancy, excessive protein intake and in the case of strenuous exercise, and then of course, we're going to think of kidney disease, kidney disease, kidney disease if we're looking at less of, uh, that creatinine clearance. And so also, continue to think about perfusion. The kidney is very, very sensitive to the amount of blood flow that it receives and if there's a lack of blood flow, kidney function is going to decline. 


You did a great job on this lesson everybody, that wraps it up. We love you guys, now go out, be your best self today, and as always, happy nursing.


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