To keep an eye on your kidney function, the estimated glomerular filtration rate (=eGFR) is determined regularly. What this value is all about, you will learn in this article.
It doesn't matter whether you have recently been diagnosed with kidney disease, are on dialysis or have even received a new kidney: Your kidney function has certainly already been determined. To measure your kidney function, a number of laboratory values are usually collected on a regular basis. They help your medical team keep track of the status and progression of your kidney disease. The functional capacity of your new kidney can also be monitored in this way. This allows the right steps to be taken in your personal treatment, if necessary.
One of the most important values in this context is called estimated glomerular filtration rate (=eGFR). The eGFR is of great importance for monitoring your kidney function, which is why it is determined at least once a year. In the case of advanced kidney disease or shortly after a transplant, the eGFR is measured even more frequently. In this way, the function of your kidney can be monitored closely. In this article, you will learn what exactly is behind this laboratory value and how it can help you to understand more about the function of your kidney.
Why are kidneys so important?
Your kidneys perform a number of different tasks in your body. For example, they produce hormones such as erythropoietin (=EPO), which stimulates the formation of new red blood cells. They also regulate your blood pressure and water balance and filter harmful substances from your blood. If concentrations of the latter are too high, they can pose a threat to your health.
For this reason, the kidneys are often referred to as your body's janitors or filters. They excrete what waste or breakdown products are produced during the day. To perform this function, a lot of blood flows through your kidneys each day. Urine is filtered from this blood, and contains all the harmful substances and breakdown products. These are then excreted later when you urinate.
What exactly is the eGFR?
The eGFR is an important parameter to measure the filtering function of your kidneys. It is often referred to as the most important parameter for accurately determining kidney function. The eGFR indicates how much fluid per minute is filtered by the small functional units (=glomeruli) of your kidneys.
If your kidneys are working well and filtering enough pollutants and waste products from your blood, then your eGFR will be high. If the function of your kidneys decreases with age or due to kidney disease, the eGFR also decreases. It is usually expressed in units of mL/min.
What are normal eGFR values?
A healthy kidney function, according to a classification of the Kidney Disease Outcome Quality Initiative (=KDOQI), is defined as eGFR values of above 90 mL/min. Lower values of eGFR are divided into individual stages and levels. These stages are also used to classify renal function in chronic kidney disease (=CKD).
In the following table, we have presented the individual stages of CKD with the appropriate eGFR values in each case:
How is eGFR measured?
Measuring your eGFR requires a blood test. However, eGFR is not determined as a direct blood value. Instead, it is always calculated using other parameters, such as creatinine or cystatin C:
- Creatinine is a breakdown product from muscle metabolism and is excreted in your urine.
- Cystatin C is a protein produced by your body cells. It is completely filtered out of your blood through your kidneys.
Both creatinine and cystatin C are filtered out of the blood by the kidneys in people with healthy kidneys. Thus, blood levels for both substances are kept almost constant.
If the filter function of the kidneys now decreases, the concentration of these two substances in the blood also increases. To calculate your eGFR, the concentration of one of these two substances in the blood is determined and inserted into one of the commonly used formulas for calculating eGFR. Some examples of recognized formulas include the CKD-EPI formula or the Cockcroft-Gault formula. But don't worry, the lab or your medical team will always do the math for you.
If your creatinine or cystatin C blood levels rise, this often indicates a decrease in your kidney function. Conversely, your eGFR decreases at the same time and can provide information about the stage of your kidney deficiency via the classification based on the table shown above.
What does the eGFR depend on?
The eGFR depends on a number of factors besides your kidney function. Because eGFR is not a stand-alone value but depends on other blood values (e.g., creatinine, cystatin C), changes in these values also affect your eGFR. In addition to your age, there are a number of other factors that can affect your eGFR. These include, for example:
- Age
- Gender
- Body weight
- Body size
- Skin color
For this reason, various approximation formulas for calculating the eGFR also take these variables into account.
Why is the eGFR so important?
As you already know, eGFR is an important indicator of your kidney function. A decrease in your kidney function can indicate the progression of an existing kidney disease, or a reduction in your transplant function. A stable, sufficiently high eGFR, on the other hand, indicates good kidney function. Note, however, that especially after transplantation the eGFR value can often be lower than in people with healthy. In this case, it is more important for your treating team that your value remains stable.
As described above, the eGFR value is used to classify the stage of existing kidney deficiency. In this way, your medical team can keep an eye on the progression of a possible kidney failure and initiate the right measures to keep your kidneys healthy and fit. If your eGFR value drops to the stage of kidney failure, it can be recognized in a timely manner and appropriate treatment can be planned accordingly. In this sense, your eGFR value is really worth its weight in gold.
Last but not least, your eGFR value can also be used to adjust the dosage of medications. If the kidneys are no longer functioning properly, the excretion of medications from the body may be impaired. Overdosing on medications can lead to serious side effects. According to your measured eGFR, the dosage of your medication can be adjusted regularly to ensure safe and effective treatment. Especially when eGFR is below 30 mL/min, the dose of many medications needs to be adjusted accordingly. Some drugs may even no longer be taken. However, you can always get more detailed information on this topic from your medical team.
How can I influence my eGFR?
Since your eGFR value reflects your kidney function, you can often influence this value yourself. The same measures that keep your kidneys fit and healthy in general can be used for this purpose. Some of these measures are:
- Eating a proper diet according to the stage of your kidney disease
- Taking your medications regularly and on time
- A healthy and stable weight
- A sufficient amount of sports and exercise
- Healthy blood pressure and blood sugar levels
For more information on these topics, check out the other articles in the Mizu app. For questions about your lab values and all around kidney health, you can also always contact your health care team.
