What are GFR norms and deviations

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Glomerular filtration rate is considered one of the most important indicators of kidney function. This characteristic is necessary to assess the work of the kidneys and determine the degree of damage to the glomeruli. Based on the interpretation of the results of the study of GFR, it is possible to determine the functionality of this organ.

Glomerular filtration rate, or GFR, is usually assessed by two main characteristics:

  • creatinine clearance,
  • serum level indicator,

Clearance is usually called the volume of plasma that the kidneys can release from foreign substances within one minute.

It should be recalled that the kidneys are a kind of filter through which many substances pass. Therefore, the main task of this organ is to ensure the removal of harmful substances and fluids from the body. At the same time, there is a filtration of nutrients that should remain in the body.

What is SCF

First of all, it should be noted that glomerular filtration is a process as a result of which the fluid with substances dissolved in it is filtered through the renal membrane.

Glomerular filtration rate is a quantitative characteristic of the formation of primary urine. The indicators are influenced by such factors:

  • the number of functioning nephrons,
  • the volume of blood passing through the vessels of the organ for a specific period,
  • the total area of ​​the capillaries involved in the filtration process.

GFR is commonly used to assess such an indicator as the total filtration function of the kidneys. GFR indicates how much blood volume can be cleared of creatinine in one minute.

A decrease in GFR will indicate a decrease in the number of active nephrons. Moreover, the rate of decline in this indicator is almost always constant. To calculate this indicator, a blood test for GFR is taken.

By comparing the obtained data with normal values, it is possible to determine the ability of the kidneys to cope with the function of cleansing blood from decay products.

GFR can be measured in units of measurement such as inulin clearance. Normally, this substance is not excreted, metabolized, reabsorbed or produced in the kidneys. In addition, it can be filtered without problems in the glomeruli.

For clearance analysis, all daily urine is required. The only exception is the morning portion. To assess the results obtained, the amount of substance in the urine is taken into account.

In men, the normal indicator is 18-21 mg/kg, in women – 15-18 mg/kg. If a lower indicator is found in the analysis, then this indicates either the presence of kidney disease or an incorrect collection of urine.

GFR is actively used to diagnose kidney disease. So, a decrease in this indicator may indicate the occurrence of a chronic form of renal failure.

In turn, an increase in the filtration rate will be a reason to suspect the presence of diabetes mellitus, lupus erythematosus, hypertension and other diseases. The detection of pathologies will indicate damage to the nephrons.

As a result, some of the nephrons die, which leads to the loss of nutrients. In addition, the cessation of the functioning of a part of the nephrons is the cause of water and toxin retention in the body.

Reasons for changing the glomerular filtration rate

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Glomerular filtration rate depends on the following factors:

  • the speed of blood flow in the kidneys. This indicator indicates the volume of plasma flowing over a certain time through the nephrons and filtering in the glomeruli of the kidneys. Normal kidney health is evidenced by a result of 600 ml/min. An indicator below this value may indicate the presence of pathological processes,
  • blood pressure level in the kidneys. If the pressure in the bringing vessel is higher than in the outgoing one, then this fact will indicate the absence of any diseases,
  • the number of functioning nephrons. A decrease in the number of functioning nephrons means the presence of pathological processes that can affect the structure of kidney cells. This deviation from the norm is the reason for a decrease in the filtration surface, the size of which affects the rate of renal glomerular filtration.
  • medications that affect creatinine. Taking medications such as cephalosporins can increase creatinine levels, resulting in increased GFR.

How to determine GFR

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Glomerular filtration rate is usually determined by calculations that take into account the ratio of creatinine in urine and blood.

You can calculate the glomerular filtration rate using special formulas. For this, calculators or computer programs are most often used. Given these possibilities, calculating GFR does not pose any particular problem.

In order to determine the glomerular filtration rate, the Cockcroft-Gold test is often used. When passing this analysis, the patient should drink 1,5-2 glasses of water or tea on an empty stomach. Due to this, the production of urine is activated.

After 20 minutes, the patient needs to completely empty the bladder. For the next hour, the patient can be at rest. Next, the first collection of all urine is carried out. In this case, it is necessary to note the time of the collection.

The next portion of urine for GFR determination is taken after another hour. The patient must have a blood test between procedures. According to the data obtained, it is determined whether the creatine clearance falls.

It is also possible to determine the glomerular filtration rate of the kidneys using the MDRD formula. In practice, 2 versions of this formula are used – full and abbreviated.

In the first case, the calculations will require data from biochemical studies. The abbreviated formula uses only sex, age, race, and serum creatinine data.

Determination of the glomerular filtration rate makes it possible to draw conclusions regarding the functioning of the kidneys and the stage of renal failure. It is this indicator that is the basis for making a prognosis of the course of the disease. On its basis, the development of treatment regimens is carried out.

Norm and deviations

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The rate of glomerular filtration rate is normally equal to:

  • 95-145 ml/min for men,
  • 75-115 ml/min in women.

In children, the norm directly depends on age:

  • 2-8 days – 39-60 ml/min,
  • 4-28 days – 47-68 ml/min,
  • 1-3 months – 58-86 ml/min,
  • 3-6 months – 77-114 ml/min,
  • 6-12 months – 103-157 ml/min,
  • from 1 year old – 127-165 ml/min.

The deviation from normal GFR values ​​is attributed to many factors. In particular, a decrease in glomerular filtration can occur as a result of the following reasons:

  • heart failure
  • deficiency of thyroid hormones,
  • profuse vomiting or diarrhea
  • problems in the liver,
  • malignant tumor of the prostate,

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A steady drop in this indicator in chronic kidney disease is evidence of pronounced CRF. If the GFR indicator drops to 5 ml/min, then this will indicate such a problem as the development of end-stage renal failure.

Deciphering the data of the conducted research allows obtaining the following results:

  • reliable. The patient has a reduced GFR, but it is exceeded in patients with normal renal function,
  • unreliable. Such results are observed in patients with unstable serum creatinine levels,
  • doubtful. This result is typical for patients with extreme values ​​of characteristics such as age, as well as body weight and volume.

GFR values ​​for disease diagnosis

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Glomerular filtration rate is a characteristic that directly affects the state of health. This indicator characterizes the filtration function of the kidneys. In addition, he can talk about the possible development of various diseases.

The doctor can make such a conclusion if the analysis results deviate from the generally accepted norm. Diagnostic methods used in modern medicine allow the most accurate determination of GFR in the kidneys.

Due to this, the specialist can give the patient an accurate diagnosis and prescribe dialysis or other procedures that can eliminate the existing problems.

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Tatyana Jakowenko

Editor-in-chief of the Detonic online magazine, cardiologist Yakovenko-Plahotnaya Tatyana. Author of more than 950 scientific articles, including in foreign medical journals. He has been working as a cardiologist in a clinical hospital for over 12 years. He owns modern methods of diagnosis and treatment of cardiovascular diseases and implements them in his professional activities. For example, it uses methods of resuscitation of the heart, decoding of ECG, functional tests, cyclic ergometry and knows echocardiography very well.

For 10 years, she has been an active participant in numerous medical symposia and workshops for doctors - families, therapists and cardiologists. He has many publications on a healthy lifestyle, diagnosis and treatment of heart and vascular diseases.

He regularly monitors new publications of European and American cardiology journals, writes scientific articles, prepares reports at scientific conferences and participates in European cardiology congresses.