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Watson-Schwartz test

A qualitative screening test for diagnosis of acute intermittent porphyria by the addition of Ehrlich's reagent and saturated sodium acetate to the urine; a pink or red colour indicates the presence of porphobilinogen or urobilinogen; the former indicates porphyria, the latter does not; therefore, positive results require further differential extraction with butanol and chloroform to eliminate false-positive results due to urobilinogen.