An arrangement, a method, and a measurement indicator, configured to measure urea in a milk sample of an animal (100). The arrangement includes a reference indicator, impregnated with a halochromic substance configured to adjust colour, based on a level of hydroxide ions of a first sub milk sample； a measurement indicator, impregnated with the halochromic substance of the reference indicator, and prepared with an enzyme configured to convert urea of a second sub milk sample, into at least one chemical substance, which in turn will influence the level of hydroxide ions of the second sub sample； a sensor configured to capture a first image of the reference indicator, and a second image of the measurement indicator； and a control unit configured to determine colour difference between the images； and configured to convert the determined colour difference into urea amount in the milk sample.
