Arrangement (500), method (400) and measurement indicator (132), configured to measure urea in a milk sample of an animal (100). The arrangement (500) comprises: a reference indicator (131), impregnated with a halochromic substance configured to adjust colour, based on level of hydroxide ions of a first sub milk sample； a measurement indicator (132), impregnated with the halochromic substance of the reference indicator (131), 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 (130) configured to capture a first image of the reference indicator (131), and a second image of the measurement indicator (132)； and a control unit (150) configured to determine colour difference between the images； and configured to convert the determined colour difference into urea amount in the milk sample.
