The ELISA (enzyme-linked immunosorbent assay) is a test which uses color change and antibodies to identify a substance. An indirect ELISA is one of three ELISA tests.
Urine varies in appearance, depending principally upon a body's level of hydration, as well as other factors. Normal urine is a transparent solution ranging from colorless to amber but is usually a pale yellow. In the urine of a healthy individual the color comes primarily from the presence of urobilin.
Also known as urochrome, urobilins are the pigment that gives urine its yellow color. Urine is usually pale yellow, but it can range from clear to a deep amber color in a healthy person. The level of yellow is determined by how hydrated a person is. A person who is very hydrated has more water to release through urinating, and thus has a lesser concentration of urobilin in their urine.