Have you ever wondered why GFR, your creatinine and urea levels, and protein and blood in your urine can be used to measure the progress of kidney disease?
If you are not yet on dialysis, the progress of your kidney disease can be examined in various ways. In the case of kidney disease, it is particularly important to see the nephrologist as early as possible and on a regular basis in order to be able to delay the disease as long as possible.
The nephrologist typically does a whole series of blood tests and urine tests, or even a kidney ultrasound. They try to understand what is happening in your body. The most important blood values are the glomerular filtration rate (GFR), your creatinine and your urea. In addition, protein (especially albumin) or blood in the urine can also detect kidney disease.
Kidney disease diagnosis based on the glomerular filtration rate (GFR)
The most important parameter for kidney function is the glomerular filtration rate. It cannot be measured directly, but requires a calculation of the clearance. Clearance is the amount of blood in which a substance is sieved out by the kidneys without obstruction during a certain period of time. Normally, the creatinine in the blood is measured and the GFR is calculated from this using various formulas (e.g. the CKD-EPI formula). In addition, it can be determined more precisely by doing a 24-hour urine test.
In order to measure the GFR in the urine, various substances can be measured during the test. These are also known as markers.
The best markers to calculate the GFR are:
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Creatinine: Creatinine has become widely accepted as a marker. However, it can happen that the kidney function is already weaker, but the creatinine does not change yet. This is then referred to as a "creatinine-blind area". The kidney only needs to be half as strong, and only then does this show up in the creatinine.
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Inulin: The measurement is quite expensive and also time-consuming. It is therefore only rarely carried out.
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Cystatin C: It already changes with a slight restriction of kidney function. Cystatin C is therefore also used as a reliable marker for calculating GFR. Unfortunately, however, the measurement is also very expensive and therefore not routinely used.
Kidney disease diagnosis based on creatinine and urea in the blood
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Creatinine is a breakdown product of creatine, which in turn supplies the muscles with energy. The creatinine level in the blood is therefore also dependent on the muscle mass of a person. Creatinine is often used as a marker but, as previously mentioned, there is this "creatinine-blind" range. So creatinine alone may not see the whole picture.
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Urea is a breakdown product of protein metabolism. Normally, you excrete it mostly through your urine. If you have too much of it in your blood, it can mean that your kidney is not doing its job adequately. It is usually only elevated in advanced kidney disease, but sometimes acute kidney disease can also lead to high levels.
Kidney disease diagnosis based on protein and blood in your urine
If the kidney is damaged, protein from the blood leaks into the urine. This blood protein (=especially albumin) is, only very weakly detectable in the urine of people with functioning kidneys. If the values are high, a possible kidney disease should be investigated more closely. To examine protein in the urine, you simply have to hold a special test strip in the urine.
Also, if you have kidney disease, there may be blood in your urine. This can also be an indication of problems with your kidneys.
