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.
If you have noticed dark yellow colored urine persistently for 3-4 days, and if you are not consuming any medicines and foods that can change the urine color, you should immediately see your doctor. Dark yellow urine can be a symptom of jaundice, cirrhosis, other liver diseases, cystitis or urinary tract infection.