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Investigation of renal plasma flow and blood flow values
Last reviewed: 04.07.2025
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Renal blood flow is the volume of blood passing through the kidneys per unit of time (1 min). Under physiological conditions, the kidneys receive 20-25% of the circulating blood volume, i.e. the value of renal blood flow in a healthy person is 1100-1300 ml/min.
Per 100 g of renal tissue, the blood supply to the kidney is 430 ml/min, which is 6-10 times higher than the blood supply to the heart, brain and other organs. Such a high level of blood supply to the kidneys is determined not by the state of their metabolism, but by the purpose of the kidneys to provide the depuration function.
The blood supply to the kidney is uneven: the cortex accounts for about 80% of the blood flow, the outer zone of the medulla - about 13%, the inner zone - 3-5% of the blood received per unit of time.
In clinical practice, direct and clearance methods of research are used to determine the magnitude of renal blood flow. These studies are carried out using a flowmeter with direct access to the kidney (in surgical practice) or the concentration of the substance being studied in the renal artery and vein is determined using the Fick principle.
In the clinic of internal diseases, to determine plasma blood flow, they use the clearance of marker substances that are not filtered during transport through the kidneys, but, getting into the vessels of the renal cortex, which wash the proximal segment of the nephron, enter the epithelium of the proximal renal tubules and are subsequently secreted into the lumen of the nephron. Since the proximal tubules are located in the cortex, then with the help of the clearance of these substances, information is obtained about the blood supply of only the renal cortex. Since marker substances do not get into erythrocytes, the obtained indicators reflect only the amount of plasma flowing through the vessels of the kidney.
[ Determination of effective renal plasma flow and blood flow
The clearance of such substances characterizes the effective renal plasma flow (EPF). To calculate the value of effective renal blood flow (ERBF), it is necessary to take into account the ratio between erythrocytes and blood plasma - hematocrit (Ht). Accordingly, the value of ERBF is calculated using the formula:
EPC=EPP: (1-Ht).
Marker substances, the clearance of which characterizes the EPP, include para-aminohippuric acid, hippuran and diodone. These research methods are labor-intensive and rather complex, for this reason they are rarely used in the clinic. Recently, clearance research methods using the radionuclide drug 1 131 -hippuran have become widespread for determining renal blood flow. The method is very simple, but requires compliance with special conditions necessary for working with radioactive substances. Normally, the EPP value is 600-655 ml/min, EPC - 1000-1200 ml/min.
Under physiological conditions, renal blood flow decreases with physical exertion, nervous excitement, and during the aging process; it increases during pregnancy, consumption of large amounts of protein, and fever.
In conditions of pathology not associated with kidney damage, a decrease in renal blood flow is detected in:
- acute and chronic circulatory failure: shock, hypovolemia, heart failure;
- acute diseases of the genitourinary system;
- dehydration and electrolyte disturbances (hyponatremia, hypokalemia and hypercalcemia);
- in a number of endocrine diseases (adrenal pathology, hypopituitarism, myxedema).
In kidney diseases, the causes of decreased organ perfusion are damage to the renal vessels (atherosclerosis, thrombosis or vascular embolism, systemic vasculitis), a decrease in the BCC as a consequence of primary kidney damage (when eliminating obstructive nephropathy, nephrocalcinosis, interstitial nephritis), a decrease in the number of active nephrons, and papillary necrosis.
Renal hyperperfusion is observed in the early stages of diabetes, SLE and the hypervolemic variant of NS.
Determination of filtration fraction
Of great importance for the characterization of renal hemodynamics is the calculation of the filtration fraction, i.e. the proportion of the plasma flow that is filtered in the glomeruli per unit of time (1 min). This value is calculated using the formula:
Filtration fraction = (SCFx100)/EPP(%),
Where SCF is the glomerular filtration rate, ERP is the effective renal plasma flow.
In a healthy person, the filtration fraction is 19-20%. Its decrease characterizes the selective suppression of the filtration function of the kidneys, a value greater than 20-22% reflects the development of hyperfiltration.
Thus, indirect evidence of hyperfiltration is considered to be depletion of the PFR (PFR <5%), values of the filtration fraction of more than 20-22%.