Usefulness of antinuclear antibody testing to screen for rheumatic diseases.

OBJECTIVE

To assess the usefulness of the indirect immunofluorescence antinuclear antibody test (FANA) using human laryngeal epithelial carcinoma cells as nuclear substrate, to screen for childhood rheumatic diseases.

STUDY DESIGN

A review of all FANA tests performed on children at British Columbia's Children's Hospital between 7 March 1991 and 31 July 1995.

RESULTS

FANA tests were positive at titres of 1:20 or greater in 41% of all subjects tested, and in 65% of all subjects in whom the diagnosis was obtained. FANA positivity occurred in 67% of those with a rheumatic disease, compared with 64% of those with a non-rheumatic disease (p = 0.4). More girls had high titre FANA positivity than boys independent of whether or not they had a rheumatic disease (p = 0.05). At a screening serum dilution of 1:40 a positive test has a sensitivity of only 0.63, and a positive predictive value of only 0.33 for any rheumatic disease. For systemic lupus erythematosus (SLE), mixed connective tissue disease (MCTD), or overlap syndrome at a screening dilution of 1:40 the test has a very high sensitivity of 0.98, but a very low positive predictive value of only 0.10, the test having slightly better characteristics for boys than girls.

CONCLUSION

Although a negative FANA test makes a diagnosis of SLE or MCTD extremely unlikely, a positive test even at moderately high titres of 1:160 or higher is found so frequently in children without a rheumatic disease that a positive result has little or no diagnostic value. It is suggested that a screening serum dilution of 1:160 or 1:320 would increase the usefulness of the test, by decreasing false positive tests, without significantly increasing false negative tests for SLE or MCTD, and would have the potential for considerable cost savings.