kidney function test, any clinical and laboratory procedure designed to evaluate various aspects of renal (kidney) capacity and efficiency and to aid in the diagnosis of kidney disorders. Such tests can be divided into several categories, which include (1) concentration and dilution tests, whereby the specific gravity of urine is determined at regular time intervals following water restriction or large water intake, to measure the capacity of the kidneys to conserve water, (2) clearance tests, which give an estimate of the filtration rate of the glomeruli, the principal filtering structures of the kidneys (see inulin clearance), and overall renal blood flow (see phenolsulfonphthalein test), (3) visual and physical examination of the urine, which usually includes the recording of its physical characteristics such as colour, total volume, and specific gravity, as well as checking for the abnormal presence of pus, hyaline casts (precipitation of pure protein from the kidney tubules), and red and white blood cells; proteinuria, the presence of protein in the urine, is often the first abnormal finding indicative of kidney disease, (4) determination of the concentration of various substances in the urine, notably glucose, amino acids, phosphate, sodium, and potassium, to help detect possible impairment of the specific kidney mechanisms normally involved with their reabsorption.
In addition to clinical and laboratory tests, the use of X-rays and radioisotopes is also valuable in the diagnosis of kidney disorders (see urography).