What Are the Factors That Affect GFR?

GFR is a measurement of the kidney’s ability to filter blood, which is necessary for maintaining fluid and electrolyte balance in the body. GFR is an important measurement as a decrease in GFR can lead to the accumulation of toxins in blood. This condition, called uremia, can cause a variety of symptoms and is life-threatening if untreated.

There are several factors that influence GFR. First, filtration occurs when pressure forces fluid through a barrier. Solutes cannot move if they are too small or too large to pass through the barrier. Hydrostatic pressure, which is created by fluid against a surface, is another factor that influences filtration. In the glomerulus, this pressure is generated by blood and glomerular capsule fluid. The lower the pressure, the greater the net movement of fluid.

Second, the size and efficiency of glomeruli also affects filtration. The glomerular filter rate is the measure of how much fluid is filtered in a minute by the kidneys. This number is expressed in mL/min.

Third, chronic kidney disease can also affect GFR. These conditions can include hypertension, diabetes, and atherosclerosis. GFR can drop by as much as 1.15ml/min annually if these diseases are present. However, some factors may increase GFR.

GFR is used for kidney function testing and to determine if a patient requires further treatment. A lower GFR could indicate kidney failure. According to the National Kidney Disease Education Program, a GFR below 60 mL/min/1.73 m2 is considered a severe kidney disease. End-stage kidney disease can also be diagnosed by a GFR of between 30 and 59 milliliters/m2.

GFR is influenced by physiological factors such as the structure of theglomerulus. The structure of theglomerulus restricts the size and charge particles that can pass through its filtration membrane. The basement membrane blocks particles smaller than 70 nanometers from passing through the basement capillaries. In addition, glomerular membrane protein repels other proteins and favors filtration of cations.

GFR is influenced by the hydrostatic and colloid osmotic pressure. During periods of stress, sympathetic nervous activity reduces blood flow to the kidney and makes more blood available to other parts of the body. The renin-angiotensin-aldosterone system helps maintain GFR by preserving blood flow to the kidney. The kidneys also have two internal autoregulatory mechanisms which keep blood pressure stable.

The GFR can be measured through creatinine clearance, which involves timed urine collection and measurement. The results are compared with the blood creatinine concentration to estimate actual GFR. Because creatinine clearance overestimates GFR by 10% to 20%, it is an imperfect indicator. However, it is easy to use and less cumbersome than a more accurate measurement.