Detection of anti-dna antibodies: A comparison between two farr assays, Crithidia luciliae and a human chromosomal substrate assay

Four commercially available assays were compared with a ¹⁴C DNA Farr assay for their ability to detect anti-DNA antibodies in 119 sera from 109 patients with systemic lupus erythematosus (SLE) and 25 control sera. The ¹⁴C DNA Farr assay was the most sensitive and specific assay (SLE, 57% positive, controls, 0%). A commercial ¹²⁵I DNA Farr assay was significantly less sensitive (SLE, 39% positive). The fluorescence human chromosomal preparation assay was as sensitive as the ¹⁴C DNA Farr assay (SLE, 58% positive) but less specific (controls, 8% positive). The immunofluorescence Crithidia luciliae assay was specific, but less sensitive (SLE, 37% positive) than the MC DNA Farr assay. Adaptation of Crithidia to immunoperoxidase did not alter its sensitivity or performance. These results confirm that the ¹⁴C DNA Farr assay, locally refined and performed by experienced hands, is the most sensitive and specific assay for anti-DNA antibodies. The ¹²⁵I DNA Farr was no more sensitive than the Crithidia assay but considerably more laborious. The human chromosomal preparation may be suitable as a rapid screening test for anti-DNA antibodies.