An evaluation of a new diagnostic test for systemic lupus erythematosus.

In a disease with such widespread and variable manifestations as systemic lupus erythematosus the diagnosis, at least in the early stages, often depends upon a clinical suspicion supported by laboratory investigations, notably the demonstration of lupus erythematosus (L.E.) cells. While this test is highly specific for systemic lupus erythematosus it has these disadvantages. In a few patients L.E. cells may not be demonstrable until late in the course of the illness and in a very few cases they may perhaps be absent throughout. The test requires expert interpretation if it is to be reliable. A really simple screening test that could be applied to the many patients with apparent rheumatoid arthritis, cutaneous lupus erythematosus, rheumatic fever, and other diseases which may be mimicked by systemic lupus erythematosus, would be invaluable for the early diagnosis of this more serious illness. Recently Jones and Thompson (1957) have described a simple protein precipitation test which they have found useful in the diagnosis of systemic lupus erythematosus and which apparently gives false positive results only in liver diseases and myelomatosis, conditions which do not usually cause clinical confusion with systemic lupus erythematosus. The present report summarizes experience of this test applied on 1,042 occasions to serum from more than 800 patients with various diseases, including systemic lupus erythematosus and discoid lupus erythematosus. Attempts have also been made to identify the protein fraction precipitated in the test. Methods The test reagent consists of a 12% solution of paratoluene sulphonic acid in glacial acetic acid. This should give a clear solution which keeps indefinitely. Old discoloured preparations of paratoluene sul-