GFR [glomerular filtration rate] is the rate at which the glomerulus filters solutes and water from the blood. It is usually expressed as volume per time, most often mL/min. It is measured by measuring the amount of a solute that is freely filtered, and neither reabsorbed nor secreted in both the urine and the blood stream. If the GFR is low, it can be a sign of renal failure.Does anyone know exactly what we need to know for GFR calculation? Does anyone know how to calculate GFR?
It is calculated by GFR= (urine concentration x urine flow)/ plasma concentration.
The urine flow is the volume of urine collected over time.
It can also be measured using radioactive isotopes or inulin. [NOT insulin!] However, the typical method is using the creatinine clearance, which uses creatinine for the solute. Due to the fact that it is minimally secreted, this can result in an overestimation of 10-20%, but considering the ease of this procedure, it is considered acceptable. Typically, the urine is collected for 24 hours to determine the amount of creatinine removed from the blood over that time.
I don't know how much of this you may need beyond a basic understanding, as I have seen some tests that were fairly basic and some that were ridiculously in-depth with the questions on physiology, but I hope this helps!
Alternatively, you can consider that if one removes 1440 mg in 24 hours, that is equal to 1 mg/minute. If the blood concentration is 0.01 mg/mL, then 100 mL/min of blood is being cleared, since, to get 1 mg of creatinine, 100 mL of blood containing 0.01 mg/mL would need to have been cleared.