Are your kidneys working properly? Let's talk about the Creatinine Clearance Test!

Have you ever thought about the little 'filter system' inside our body? Just like the oil filter in a car, the kidneys are one of the most important organs that filter and remove waste products from our body. As long as they are working properly, we have no problems. But if their function decreases even slightly, various diseases can arise in the body. So, today we are going to talk about an important test that can be done to check whether your kidneys are working properly. That is the Creatinine Clearance Test.

Simply put, what is this creatinine clearance test?

This may sound like a scientific name, but it's actually quite simple. This test measures how well your kidneys are working. To do this, they measure the amount of creatinine in a urine sample and a blood sample. Based on these results, your doctor can determine whether you have kidney disease or not.

So what is this creatinine?

Think of the muscles in our body as like the engine of a car. This engine needs energy, that is, fuel, to work. Creatine is a chemical that provides energy to our muscles. When we walk, run, or lift weights, these muscles work, that is, they use energy.

When you use energy like this, like smoke coming out of an engine, a waste product called creatinine is formed and added to the blood. This is useless to the body. So, what two healthy kidneys do is filter this blood thoroughly and remove the unnecessary creatinine with urine.

But, imagine that your kidneys are functioning a little less. What happens then? Just like when a car's muffler is blocked, the smoke is trapped and cannot escape properly, the kidneys are also unable to filter this creatinine properly and expel it. Then the creatinine level in the blood increases above normal. That's what this test looks for.

This test involves collecting your urine over a 24-hour period, as well as a blood sample. Using both samples, it is calculated how much creatinine your kidneys have filtered out over a 24-hour period.

However, doctors don't often use the creatinine clearance test these days because collecting urine over a 24-hour period is a bit cumbersome. Instead, the easier, single-dose blood test called eGFR (estimated Glomerular Filtration Rate) and the single-dose urine test called uACR (urine albumin-creatinine ratio) are now the most commonly used.

What are the symptoms of elevated creatinine levels?

In most cases, elevated creatinine levels in the blood mean that there is some damage to the kidneys and their function is impaired. When kidney disease develops, there may be no symptoms in the early stages. That is the most dangerous. But as the disease progresses, you may start to feel things like this:

So when will this test be done?

As we mentioned earlier, the most common blood test now is the eGFR. However, there are some special cases where the doctor feels that the results of the blood test alone are not enough and are not completely accurate. That is when the doctor refers to the creatinine clearance test, which involves collecting a 24-hour urine sample.

For example:

• Someone with a lot of muscle mass: Imagine a bodybuilder who has worked out hard at the gym. Because he has a lot of muscle mass, he produces more creatinine than the average person. So, if you look at it only through the eGFR blood test, his creatinine level may simply show a high value. This can lead to a wrong conclusion that there is a problem with the kidneys.
• Someone with very low muscle mass: Similarly, someone who is very thin and has little muscle mass will produce less creatinine. Therefore, the eGFR value may indicate a better than true kidney condition.

In such cases, the doctor may ask you to do this 24-hour test to get a more accurate picture.

How to prepare for the test?

To perform this test correctly, you will need a little preparation on your part. Your doctor or the lab will advise you on this.

• Urine collection container: The lab will give you a special large container (bottle) to collect your urine in. They will also give you instructions on how to store it for 24 hours (for example, they may tell you to refrigerate it).
• Follow the instructions exactly: The success of this test depends on you. You need to collect every drop of urine you pass over a 24-hour period into the container. If you accidentally flush it down the toilet even once, the entire test result may be incorrect. If that happens, you will have to start over.
• Tell your doctor about any medications you are taking: Some medications you are taking (e.g., some antibiotics, stomach pain medications) can affect the results of this test. So tell your doctor about all the medications you are taking. Only stop taking them temporarily for the days before the test if your doctor tells you to. Never stop taking medications on your own.
• Food and drink:Usually, you can eat normally. However, sometimes, your doctor may ask you to fast the night before the test. You may also be asked to avoid eating meat before and on the day of the test. Because meat contains a lot of creatine, eating meat can temporarily increase the amount of creatinine in your body. This can give you false results.

What happens during the test?

Make a note of the exact time you want the test to start. For example, if you are starting the test at 8am, you would do the following:

1. Collect your first urine sample: At 8 a.m., empty your urine into the toilet as normal and flush it. Do not collect it. This is when your 24-hour period begins.

2. Then collect everything: From there, until 8 a.m. the next morning, collect that urine into the container provided by the lab every time you urinate. You should also collect it if you get up at night to urinate.

3. Final sample: At 8 am the next day (when 24 hours have passed), even if you don't feel like urinating, try to collect some urine in the same container. This is the final sample.

4. Blood Donation: After the 24-hour urine collection is complete, you will need to go to the lab and give a blood sample. Most of the time, the blood is taken at the same time you hand over the urine container to the lab.

This blood sample is used to measure the level of creatinine in the blood (serum creatinine). Then, the amount of creatinine in the urine, the amount in the blood, and the total amount of urine collected are put into a mathematical formula to calculate your creatinine clearance value.

How to understand the results?

When the test results come back, leave it to the doctor to interpret them, because you can't diagnose an illness by looking at a single number.

• If the creatinine clearance value is high: This usually means that the kidneys are not functioning properly. However, this is not always the case. Sometimes the results can be different due to other reasons. For example:
• Heart failure
• Bladder conditions
• Dehydration (lack of water in the body)
• Other kidney damage
• Can the results be wrong?:Yes, some factors may affect the accuracy of the results.
• Not collecting urine properly.
• Taking medications that affect the results.
• Excessive intake of protein-rich foods (meat, fish, eggs).
• Pregnancy.
• Too much or too little muscle mass.
• Excessive exercise on the day of the test.

Therefore, please discuss any questions or concerns you have about your results with your doctor.

Some frequently asked questions

Does drinking water lower creatinine?

Yes, drinking a lot of water can temporarily lower your blood creatinine levels. So, don't drink too much water out of habit, hoping to get a "good result" on the test. Drink the same amount of water you normally drink in a day. That's how you get the most accurate result that reflects your body's true state.

What creatinine level indicates kidney failure?

This is very important. You can't tell if someone has kidney failure just by looking at their creatinine level. A doctor comes to that conclusion after considering the results of a bunch of tests, your age, gender, and muscle mass. The normal values ​​for a blood test (serum creatinine) are as follows:

Again, remember: these values ​​can vary slightly from lab to lab. And don't be alarmed if they're a little higher than this value. Your doctor is looking at your GFR. That's the most important measurement.