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Glomerular filtration rate, or simply GFR, is a laboratory measurement that allows the general practitioner and nephrologist to assess the functioning of the person's kidneys, and this measure is important for the diagnosis and verification of the stage of kidney disease chronic disease (CKD), which makes the GFR also essential for establishing the best treatment, if necessary.
In order to calculate the glomerular filtration rate, it is necessary to take into account the person's sex, weight and age, since it is normal for the GFR to decrease as the person ages and is not necessarily indicative of injuries or kidney changes.
There are several calculations proposed to determine the glomerular filtration rate, however the most used in clinical practice are those that take into account the amount of creatinine in the blood or the amount of cystatin C, which is the most studied currently, since the amount of creatinine can be influenced by other factors, including diet, it is not, therefore, an appropriate marker for the diagnosis and follow-up of CKD.
How GFR is determined
Glomerular filtration rate is determined in the laboratory through calculations that must take into account mainly the age and gender of the person, as these factors affect the result. However, for GFR to be calculated, a blood sample must be collected so that creatinine or cystatin C can be measured, according to the doctor's recommendation.
Glomerular filtration rate can be calculated taking into account both the creatinine concentration and the cystatin C concentration. factors such as diet, physical activity, inflammatory diseases and amount of muscle mass, and thus does not necessarily represent kidney function.
On the other hand, cystatin C is produced by nucleated cells and is regularly filtered in the kidneys, so the concentration of this substance in the blood is directly related to the GFR, being, therefore, a better marker of the functioning of the kidneys. kidneys.
What is it for
The glomerular filtration rate aims to verify the functioning of the kidneys, as it takes into account the dosage of substances that are filtered in the kidneys and are not reabsorbed into the blood, being essentially eliminated in the urine. In the case of creatinine, for example, this protein is filtered by the kidneys and a small amount is reabsorbed into the blood.
However, when there are changes in the kidneys, the filtration process can be altered so that there is less creatinine being filtered by the kidneys, resulting in a higher concentration of creatinine in the blood and a decrease in the filtration rate glomerular.
Normal TFG values
As the glomerular filtration rate can vary according to the gender and age of the person, the GFR values when calculated with creatinine are:
- Normal: greater than or equal to 60 mL/min/1, 73m²;
- Kidney failure: less than 60 mL/min/1, 73m²;
- Severe renal failure or renal failure: when less than 15 mL/min/1, 73m².
According to age, normally the normal GFR values are:
- Between 20 and 29 years: 116 mL/min/1, 73m²;
- Between 30 and 39 years: 107 mL/min/1, 73m²;
- Between 40 and 49 years: 99 mL/min/1, 73m²;
- Between 50 and 59 years: 93 mL/min/1, 73m²;
- Between 60 and 69 years: 85 mL/min/1, 73m²;
- Over 70 years: 75 mL/min/1, 73m².
Furthermore, GFR values may vary according to whether or not the person is of African descent, with values considered normal for both cases above 90 mL/min/1.73m².
The values may vary according to the laboratory, however, when the GFR is lower than the normal reference value for age, the possibility of kidney disease is considered, and other tests are recommended for to complete the diagnosis, such as imaging tests and biopsy. In addition, based on the GFR values obtained, the doctor can verify the stage of the disease and, thus, indicate the most appropriate treatment.