Difference Between Glomerular Filtration Rate vs. Renal Plasma Flow

Main Difference

The main difference between glomerular filtration rate and renal plasma flow is that glomerular filtration rate is a test to check kidneys working whereas renal plasma flow is the volume of blood reach to the kidneys per unit time.

Glomerular Filtration Rate vs. Renal Plasma Flow

Endogenous substances and several drugs have been used as markers to measure GFR. These markers (inulin and creatinine) are carried to the kidney by the blood through the renal artery and are filtered at the glomerulus. Therefore, the rate at which these all drug markers are filtered from the blood into the urine per unit time indicates GFR. For renal plasma flow measurement, p-amino hippuric acid is used as a marker. This substance is filtered by the glomeruli and secreted by the tubular cells. Active secretion is very rapid for this substance. The clearance of p-amino hippuric acid reflects renal plasma flow. GFR rate for average adults is 90 or higher, but it can be range from 60 to 89 for older people (age above 60 years). A GFR below 60 is not normal and should seek doctors’ advice on this. GFR test should be repeated. A GFR value below 60 for continuously three months indicates chronic kidney disease. A GFR below 15 indicates kidney failure. Renal plasma flow value is about 1.2 to 1.3 L/min or 425 to 660 mL/min.

Comparison Chart

Glomerular Filtration RateRenal Plasma Flow
The glomerular filtration rate is the amount of blood passes through the glomeruli each minute.Renal plasma flow is the volume of plasma delivered to the kidneys per unit time.
Purpose
To assess kidneys functionsTo assess renal function
Normal Rate
90 or higher on the average person1.2 to 1.3 L/min in a normal 70kg adult
Diseases
Chronic kidney diseaseRenal hypertension
Mathematical Formula
Cockcroft Gault formulaeRPF= RPF. Extraction Ratio
Measuring Markers
Inulin and CreatinineP-amino hippuric acid

What is the Glomerular Filtration Rate?

A glomerular filtration rate is an indicator number of kidneys health. It tells that either kidney is usually working or not. Kidneys perform different important roles; one of them is to remove the waste material and excess fluid from the circulating blood. Kidneys filter waste material from the blood and excrete it through the urine out of the body. When kidneys working become disturbed then important substances like protein are excreted out and waste material become part of blood. GFR is the best way to check the normal working of kidneys. GFR is the amount of blood that passes through the glomeruli that are the filtering tubes of kidneys, per unit time. GFR cannot be measured directly. It has calculated through a mathematical formula. Glomerular filtration rate needs to be determined using the method from the quantity of creatinine in blood along with other factors. Age, race, and gender are other factors on which GFR depends. Creatinine is a waste material produced by the body’s muscles. Kidneys usually keep the level of creatinine at the right level. Although creatinine level alone is the best way to check kidney function, it is significant to do blood tests to estimate GFR. GFR rate tends to decrease with the increase of age without any kidney disease. Older people need to check GFR more often. They also advised avoiding medications which cause damage to the kidney or reduce the dose of such medicines. Someone with kidney disease failure needs to do dialysis or kidney transplant for survival.

What is Renal Plasma Flow?

Renal plasma flow has confused with renal blood flow sometimes. Renal blood flow is the volume of blood to the kidneys per unit time whereas renal plasma flow is just the volume of plasma delivered to the kidneys per unit time. Practically it is difficult to measure renal plasma flow directly, so sufficient renal plasma flow has measured which is the volume of plasma cleared of p-amino hippuric acid per unit time. The mathematical formula for the renal plasma flow comes from Fick’s law which is a mass balance calculation. In humans, kidneys receive almost 25% of cardiac output nearly 1.2 to 1.3 L/min in an average 70kg adult. It passes about 94% to the cortex. Renal blood flow is closely related to renal plasma flow. Both terms are generally applied to arterial blood delivered to the kidneys, both renal blood flow, and renal plasma flow can be used to quantify the volume of venous blood exiting the kidneys per unit time. PAH is freely filtered and is not reabsorbed and secreted within the nephron. It means not all PAH crosses into the primary filtrate in Bowman’s capsule and remaining PAH in the vasa recta is taken up and secreted by epithelial cells of the proximal convoluted tubules in the lumen. In this way, low PAH doses are almost completely cleared from the blood during a single pass through the kidney. RPF is proportional to the difference in pressure between the renal artery and vein but inversely proportional to the vasculature resistance.

Key Differences

  1. The glomerular filtration rate is the amount of blood passes through the glomeruli per minute whereas renal plasma flow is the volume of plasma reaches to kidneys per unit time.
  2. The glomerular filtration rate is used to check kidneys functions whereas renal plasma flow is used to assess renal function.
  3. The normal range of glomerular filtration rate is 90 or higher whereas the average value of renal plasma flow is 1.2 to 1.3L/min.
  4. Abnormality in the glomerular filtration rate can cause chronic kidney disease whereas anomaly in renal plasma flow can result in renal hypertension.
  5. For glomerular filtration rate assessment inulin and creatinine are used as markers whereas, for renal plasma flow, p-amino hippuric acid is used as an indicator.

Conclusion

It has concluded that although different markers are used to calculate glomerular filtration rate and renal plasma flow, both aspects are significant to indicate the functioning of kidneys.

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