For some parasite species, an alternative to counting worm eggs is to test a blood or milk sample. These tests are based on the detection of antibodies (proteins in the bloodstream, produced as an immunological response to foreign organisms), and are available as commercial tests offered by some laboratories. The detection of parasite antibodies in the blood or milk indicates that the animal has had exposure to the parasite, either as a current infection or as past contact. These tests are highly specific to particular parasites, and commercially available for very few species, including:
These tests are mostly used by veterinarians for diagnostic investigations, although bulk milk antibody tests for small brown stomach worm are more widely used in the dairy industry in some countries.