Creatinine Clearance – Clinical Application of Creatinine

00:00 Now to correlate with GFR. What kind of things that you want to keep in mind. As you said, as one gets older, then your GFR starts dropping.

00:11 Your renal failure per se but you always want to keep that mind because you do not know as to what the patient has been exposed to. Was it diabetes mellitus? What is it drugs that were nephrotoxic. Regardless as the patient gets older, then their creatinine clearance is going to drop by 1 milliliter per minute after the age of 50. What does that mean to you? Normally speaking in older patient above the age of 50, what do you expect your plasma creatinine levels to be? On the higher side or lower side if your GFR starts dropping after the age of 50? Obviously increased okay. So if by chances you are reading the lab and interpreting it and you are attending or boards or whatever asking you, what does this mean to you? Keep in mind that your creatinine levels plasma will be elevated at the age of 50. Useful in detecting renal dysfunction. Okay now. You want to spend a little bit time here and take a look at what the creatinine clearance formula is measuring and the bottom line is this though. You definitely want to pay attention. UV/P. Take a look at U. What is U? That is the urine concentration, milligrams per deciliter. It is important that you pay attention and highlight in your head milligrams over decilitres being the unit times V. That is the flow rate and that would be once again millilitres per minutes. Units are important every once in a while you will get an equation and you are responsible for calculating it and if you keep the units in mind, trust me it will you help you a lot. What is this for? This is the equation for clearance. Think UV, think ultraviolet if that helps you in the numerator. So on top we have U x V. What is U? Urine concentration x V the flow. Draw a line a slash so it is divided. So in the denominator, you will have the plasma. It is UV/P. If that helps you remember. The P will be the plasma concentration of creatinine and that will be milligrams per deciliter and there you have it as being the equation for clearance in general. When you are going to play around with this quite a bit all that you do at this point is learn the big formulas. The big formulas from cardiology, the big formulas in nephrology and all you do is to start manipulating it and once you do, you will get the answer. No doubt.

02:42 So here what are we looking for clearance wise? We are looking for the clearance of creatinine and we have UV/P and once we figure all this out well you get the clearance of that particular agent. What is the agent here? Creatinine. So at some point in time maybe I am asking the question about clearance of some other substance and once they do use the same formula and you substitute the creatinine with the other substances that they might be asking about. Normal adult creatinine clearance. 97 to 137. What is that normal? In general creatinine clearance, less than 100 is abnormal. This is not the same thing as plasma creatinine.

03:29 Plasma creatinine is what was measured in the blood. Where we are measuring this creatinine? What has been cleared? So less than 100. You want to suspect. Oh! the patient is having a pathology of some sort. There is some kind of renal failure. Less than 10. Oh! boy absolutely look at this. Absolute renal failure, less than 10. That means that the kidney is not filtering anything. If its not filtering anything, then how in the world are you going to clear anything? You're not? It is going to much much much less. Now as a caveat, we talked about elderly patients. It is absolute imperative that you, before you begin administering any drugs such as aminoglycosides, gentamicin what not, aminoglycosides antibiotics. It is absolutely imperative that you figure out the renal function for us because if that patient is not able to properly evacuate that drug from the kidney and especially if that drug is known to be a nephrotoxic agent, then you are going to then bring about acute renal failure and you don't want that specifically acute tubular necrosis. At some point when we further get into nephrology, we will start talking about renal failure. We will then divide acute and chronic renal failure. Under acute renal failure we will talk about acute tubular necrosis.

04:44 Under acute tubular necrosis, we will talk about two major divisions. One will be ischemic and one will be nephrotoxic with things like drugs. It is important that you figure out the proper renal function of an elderly patient which you expect to be on the higher side in plasma creatinine and the creatinine clearance will give you the actual renal functionality so that you can adjust the dose of the nephrotoxic drug so that you don't kill the kidney of the patient. Are you putting things together now? It is all about understanding the physio, understand the normal, how to use the formula that has been given to you and then obviously the clinical application and how you will then apply this in your clinical wards, clinical practice.