Glomerular Filtration Rate <80ml/min, Is Renal Insufficiency?

The glomerular filtration rate is an important measure used by nephrologists to help patients with chronic kidney disease assess kidney function.

Glomerular filtration rate specifically refers to the ability to clear a substance in plasma per unit time, that is, how many milliliters of plasma can be removed by the kidneys per minute, and corrected by body surface area. In detail, the heart pumps 5000ml of blood per minute, a quarter of which goes to the kidneys. The glomerulus filters out one-tenth of this part of the blood to form original urine, that is, 125ml of original urine is generated per minute, that is to say, the ideal glomerular filtration rate of healthy people is about 125ml/min. The glomerular filtration rate is generally above 90ml/min.

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The glomerular filtration rate is related to age, gender, and physique. There are differences in height, shortness, fatness, and thinness between people, so there are great individual differences. As long as the glomerular filtration rate is greater than 90 ml/min, it can basically be considered that the renal function is not impaired. Accurate assessment of glomerular filtration rate is of great significance to correctly determine the staging of chronic kidney disease, and it is often used clinically to adjust the dose of drugs, especially drugs that are excreted by the kidneys and have a narrow therapeutic window. Glomerular filtration rate can also determine whether kidney donation and kidney transplantation are possible.

With age, all organs in the human body are aging, and the kidneys are no exception. From about the age of 40, renal function will decline year by year. The most intuitive data is that the glomerular filtration rate decreases by 0.8-1.1ml/min per year. Assuming that a male's glomerular filtration rate is 100ml/min at the age of 40, and when he is 60 years old, the glomerular filtration rate is 80ml/min. According to the above theory, it is completely possible, so it is impossible to say that a male 60-year-old man with a glomerular filtration rate of 80 ml/min has progressed to chronic kidney disease stage G2.

The pathological grading of the kidney and the renal function grading are completely independent and not the same thing. The grading in the above table is for patients with confirmed kidney damage. For a healthy elderly person, if there is no direct evidence of kidney damage, as long as the glomerular filtration rate is greater than 60ml/min, it can be considered normal. Physiological decline.

Modern people have a high prevalence of basic diseases such as hypertension, diabetes, hyperuricemia, and hyperlipidemia. These are important factors that lead to the pathological decline of the glomerular filtration rate. If chronic diseases are not intervened, then At the age of 40, the glomerular filtration rate is 100ml/min, and at the age of 60, the glomerular filtration rate is 50ml/min.

How to accurately calculate the glomerular filtration rate?

traditional measurement

Because of the limitations of traditional methods of measuring GFR, researchers have developed a number of serum creatinine-based assessment formulas to assess GFR. The plasma concentration of cystatin C is independent of muscle mass and renal tubular secretion and can be used as a substitute for creatinine to assess renal function and glomerular filtration rate [1].

Does the glomerular filtration rate go from low to high?

The answer is yes.

The Chinese people generally use the formula of the Simplified Diet Modification in Kidney Disease Study (MDRD).

Simplified MDRD formula: estimated glomerular filtration rate=186×serum creatinine (mg/dl)-1.154×age-0.203 (ml/min1/1.73m2)

First of all, there is a physiological decline. For example, a 25-year-old man occasionally eats a lot of barbecued meat at a dinner party with his colleagues. We all know that part of the serum creatinine comes from the meat in the diet. l increased to 150μmol/l, the calculated glomerular filtration rate decreased from 125ml/min to 80ml/min. When the light diet was subsequently resumed, the serum creatinine also returned to the previous level, and the glomerular filtration rate also rose to about 125ml/min and remained stable, so it cannot be said that the man's renal function suddenly deteriorated after dinner. 

There are also cases of pathological decline. For example, in a patient with diabetic nephropathy, the glomerular filtration rate is 50ml/min. This is a pathological situation. This patient can only control the basic conditions by taking medicines on time and reviewing them regularly. The disease is no longer worsening, and it is possible to fix itself in the G3a stage. In this case, the glomerular filtration rate generally does not change from low to high.

The glomerular filtration rate is not directly measured clinically but is calculated. This result is related to many factors, so when seeing a glomerular filtration rate value, the doctor will consult the patient's recent situation. Give a more accurate assessment of renal function data.

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