Because of the time and skill involved in obtaining a positive L.E. preparation, a simple, clinically adaptable macroscopic precipitation test for systemic lupus erythematosus has been proposed. This has received considerable interest,1-4 although no mention of it has been made as yet in the dermatologic literature. In brief, the test is done by the addition of a 12% solution of p-toluene sulfonic acid in glacial acetic acid to serum or plasma. The resultant precipitate indicates a positive test. At present, this precipitant has not been identified.
Recent reports indicate that, although the test is of interest, contrary to the original work, it has no value for the specific diagnosis of lupus erythematosus. It does not help to differentiate systemic lupus erythematosus from the related disorders. Dubois2 has said: "It is of value only when positive, and then it indicates the presence
BARKOFF JR, SAWYER F. The P-Toluene Sulfonic Acid Test for Systemic Lupus Erythematosus. AMA Arch Derm. 1959;80(4):445–446. doi:10.1001/archderm.1959.01560220055012
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