Is the lepromin skin test helpful in making a diagnosis of leprosy?

No, but it is useful in classifying leprosy into the various subtypes. Lepromin is a crude preparation of killed bacteria from a lepromatous nodule or from infected armadillo liver. An intradermal injection of 0.1 mL of lepromin is read at 48 hours for erythema (Fernandez reaction) or at 3 to 4 weeks for a papule or nodule (Mitsuda reaction). Patients with tuberculoid leprosy have strongly positive reactions, while dimorphous and lepromatous patients are usually negative. The reaction in indeterminate leprosy is variable.