Learn about glomerular filtration rate test

The article was professionally consulted with Specialist Doctor I Nguyen Hung - Doctor of Endocrinology - Department of Medical Examination & Internal Medicine - Vinmec Danang International General Hospital.

The kidneys are an important organ in the body that is directly involved in the function of filtering blood and eliminating substances out of the body. The glomerular filtration rate (GFR) is expressed through the creatinine clearance index and other substances in the body.

The glomerular filtration rate (GRF) is defined as the amount of blood filtered through the kidneys in a given unit of time, here, in terms of minutes.
The glomerular filtration rate (GRF) test is an indicator used to assess the functional status of the kidneys by assessing the purification index of some substances in the body such as creatinine, urea..., not using it. used to directly diagnose kidney diseases. In the composition of the kidney, the glomerulus is considered an important functional unit, responsible for filtering the blood, all substances that are reabsorbed or eliminated through excretion must pass through the glomerular filter. Therefore, this test is called a glomerular filtration rate test.
When two healthy kidneys, on average each day can filter about 200 liters of blood to produce about 2 liters of urine. In contrast, when the kidneys are damaged or have kidney diseases, kidney function is reduced, leading to reduced filtering capacity and waste products will be gradually accumulated in the blood. At this time, the appointment of tests is absolutely necessary to evaluate the functioning of the kidneys.
The test to evaluate the glomerular filtration rate is done by examining and measuring the amount of creatinine in the blood. Creatinine is one of the products made during muscle movement, then enters the bloodstream and is filtered out of the blood by the glomerulus. When the kidneys are damaged or have problems affecting the filtering function of the glomeruli, the result is that creatinine is not completely filtered out of the blood but also remains in the blood in high concentrations. Therefore, the quantitative assessment of creatinine in the blood is an important factor in assessing kidney function.
The function of the kidneys to purify substances can be affected by many different factors, so if you want the most accurate assessment of the glomerular filtration rate, it is necessary to have an accurate calculation formula based on the test results. can check.
Kidneys contain many different functional units called nephrons. In the process of filtration and elimination of substances, the nephrons usually act independently of each other. Therefore, to calculate the standard glomerular filtration rate, the glomerular filtration rate of both kidneys is estimated as the glomerular filtration rate of each nephron multiplied by the total number of nephrons constituting the kidney. The number of nephrons of each body is different, the degree of filtration of each nephron in an individual is also different, so the glomerular clearance of each body is obviously different.

The formula for calculating the glomerular filtration rate (GRF): Currently, there are many different equations proposed to be applied to calculate the glomerular filtration rate. However, for the convenience of calculation and application of an easy-to-understand formula, people have researched and proven the formula for calculating glomerular filtration rate as follows:
Glomerular filtration rate = Nephron number x Glomerular filtration rate kidney of 1 Nephron. Glomerular filtration rate = Nephron count x Ultrafiltration coefficient x Filtration area x (PCG - PBC) - (GC - BC) Where:
K is the ultrafiltration coefficient S is the filtration area PCG is the hydrostatic pressure of the glomerular capillaries PBC is the hydrostatic pressure of the Bowman cavity GC is the oncotic pressure of the glomerular capillaries BC is the colloidal pressure of the Bowman compartment Based on the results of the creatinine clearance test, evaluate the glomerular filtration rate Renal function is divided into the following stages:
Stage 1: Glomerular filtration rate greater than or equal to 90 ml/min/1.73m2.
Kidney function still works normally. Clinically, there are some abnormal symptoms that warn of the risk of kidney damage such as positive blood urine test, high protein level... Stage 2: Filtration glomeruli in the range of 60 - 90 ml/min/1.73m2.
Kidney function is slightly impaired. There may or may not be clinical manifestations. Note that for clinical cases where the patient has no symptoms, do not rush to conclude the diagnosis, but allow the patient to follow up for a longer time, control both the paraclinical test index and the clinical signs. clinical sign. Stage 3: This stage has 2 different levels: stage 3A, glomerular filtration rate from 45 - 59 ml/min/1.73m2. Stage 3B, glomerular filtration rate is in the range of 3--40 ml/min/1.73m2.
The functioning of the kidneys is moderately impaired. Clinically with or without renal disease. Stage 4: The glomerular filtration rate ranges from 15 to 29 ml/min/1.73m2.
Kidney function is severely impaired, examination may or may not detect kidney-related pathology. Stage 5: At this stage, the glomerular filtration rate is low, below 15 ml/min/1.73m2.
Common in patients with end-stage renal failure, kidney function is almost completely reduced.

Creatinine clearance in the body is strongly related to muscle performance. Certain activities or diseases as well as eating and drinking habits can also change the creatinine level in the blood. Therefore, when doing a test to check creatinine clearance to evaluate the glomerular filtration rate, some of the following cases should be kept in mind:
Cases where the patient has inactive muscles such as motor paralysis, muscle atrophy ... Persons with birth defects or due to an accident resulting in missing a limb, may be missing an arm, a leg or both In case of malnutrition or acute kidney failure Patients swelling, increased water retention in the body Pregnant women and children Some medications can change the amount of creatinine in the blood, such as non-steroidal anti-inflammatory painkillers, cholesterol-lowering drugs, antifungal drugs, antibiotics, anti-viral drugs... In the body, the kidneys are an important organ, playing a key role in filtering the blood and creating urine to excrete waste out. When kidney function is impaired, it will lead to many other consequences that can have a significant impact on the patient's health. It is absolutely necessary to do tests to check and evaluate the glomerular filtration rate so that it can help support the diagnosis and prognosis of the disease and provide timely treatment to avoid complications. after.