Comparison between the Latex Nucleoprotein Test and the Fluorescent Method for the Demonstration of Antinuclear Factor

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Abstract
A comparative study of the results obtained by the fluorescent antibody method for the detection of serum anti-nuclear factor and a commercially available latex nucleoprotein reagent ("L.E. Test") has been carried out on a series of 525 sera. The latex nucleoprotein test was positive in only eight out of 24 cases of clinically-defined systemic lupus erythematosus, in all of which the fluorescent test was positive. Infected sera were found to be responsible for five false positive latex nucleo-protein reactions; however, after centrifugation and subsequent testing of the supernate, these sera became negative. The exclusion of the false positive reaction by centrifugation did not interfere with the genuine latex positive reaction. The latex nucleo-protein test was positive, after infection of the serum had been excluded, in two individuals in whom the fluorescence test was negative[long dash]a case of discoid lupus, and a relative of a patient with an undefined collagen disease. To account for the relative hyposensitivity of the latex nucleoprotein reaction, we have considered the possibility of inhibition by free DNA, which we have shown to be present in the latex reagent. When coated particles resuspended in DNA free buffer were substituted in the test, however, no significant increase in sensitivity was found. It does not therefore appear that this test is a satisfactory substitute for the immuno-fluorescent procedure in the detection of serum antinuclear factor.