To assess the specificity and sensitivity of antiperinuclear factor (APF), anti-keratin antibody (AKA), anti-Sa antibody and anti-RA33 antibody in the diagnosis of RA.
128 patients with RA, whose durations were within 1 year, were included. APF and AKA were detected by indirect immunofluorescence on the human buccal mucosa cells and the straum corneum of Wistar rat esophagus. Anti-Sa antibody and anti-RA33 antibody were examined by Western blotting. Sa antigen was extracted from human placenta while RA33 antigen from Ehrlich cells.
(1) The specificities and sensitivities of APF, AKA, anti-Sa antibody and anti-RA33 antibody were 91.4% (224/245) & 35.2% (45/128), 90.2% (221/245) & 32.0% (43/128), 90.6% (222/245) & 33.6% (43/128), 89.8% (220/245) & 28.9% (37/128), respectively, versus 72.3% (177/245) & 44.5% (57/128) for rheumatoid factor (RF). There were no statistical differences in the specificity between the four antibody groups and RF until 1:128 were taken as positive titer. Among 71 patients with RF-negative RA, 15 (21.1%) were positive for APF, 18 (25.4%) positive for AKA, 21 (29.6%) positive for anti-Sa antibody and 17 (23.9%) positive for anti-RA33 antibody. (2) Specificity and sensitivity were 95.1% (233/245) and 46.1% (59/128) respectively when two of the four antibodies turned out to be both positive. If three or more kinds were detected simultaneously, specificity was as much as 99.6% (108/128). (3) Statistical difference was found among the four groups defined by the number of positive antibodies in radiographic stage and patients assessment of illness.
(1) Dictation of APF, AKA, anti-Sa antibody and anti-RA33 antibody can greatly improve the specificity of diagnosis of early RA and serve as a complement when RF is negative. (2) Combined detection of the above four antibodies has a better discrimination ability as a laboratory criterion than that of RF. (3) Three or more positive antibodies may be an indicator of severe bone erosion and emergent demand for early treatment with better outcome.