The Sabin-Feldman test is a serological test to diagnose toxoplasmosis. The test is based on the presence of certain antibodies that prevent methylene blue from entering the cytoplasm of toxoplasma organisms. The patient's serum is treated with Toxoplasma trophozoites and complemented as an activator, and then incubated. After incubation, methylene blue is added. If anti-Toxo antibodies are present in the serum, because these antibodies are activated by complement, they lyse the parasite membrane and the trophozoites will not be stained (positive result), and if there are no antibodies, trophozoites with intact membrane are stained and appear blue under microscope (negative result)
wiki
