Renal function is the degree of efficiency the kidneys filter blood. So, The terms “renal function” and “kidney function” mean the same thing. For many people with reduced kidney function, a kidney disease is also present and will get worse. Serious health problems occur when people have less than 25 percent of their kidney function. When kidney function drops below 10 to 15 percent, a person needs some form of renal replacement therapy—either blood-cleansing treatments called dialysis or a kidney transplant—to sustain life.
Renal function is an indication of the state of the kidney and its role in renal physiology. Glomerular filtration rate (GFR) describes the flow rate of filtered fluid through the kidney. Creatinine clearance rate (CCr) is the volume of blood plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. Both GFR and CCr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result (eGFR and eCCr).
The results of these tests are important in assessing the excretory renal function of the kidneys. For example, grading of chronic renal insufficiency and dosage of drugs that are primarily excreted via urine are based on GFR (or creatinine clearance).
It is commonly believed to be the amount of liquid filtered out of the blood that gets processed by the kidneys. Physiologically, these quantities (volumetric blood flow and mass removal) are only related loosely.
Most doctors use the plasma concentrations of the waste substances of creatinine and urea, as well as electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease.
Unfortunately, blood urea nitrogen (BUN) and creatinine will not be raised above the normal range until 60% of total kidney function is lost. Hence, the more accurate Glomerular filtration rate or its approximation of the creatinine clearance are measured whenever renal disease is suspected or careful dosing of nephrotoxic drugs is required.
Another prognostic marker for kidney disease is Microalbuminuria; the measurement of small amounts of albumin in the urine that cannot be detected by urine dipstick methods.