Simultaneous combined measurement of antikeratin antibody and rheumatoid factor: additive value in the diagnosis of rheumatoid arthritis

ABSTRACT

Rheumatoid arthritis [RA] is a systemic inflammatory autoimmune disease of unknown etiology characterized by chronic polyarthritis. Its highly variable and unpredictable course is the underlying reason for the search for new and more sensitive and specific laboratory markers. The only serologic test routinely used in RA assessment is the determination of rheumatoid factor [RF] in the serum. Although RF has sensitivity up to 80%, still it lacks specificity. To evaluate a new marker "antikeratin antibody" [AKA] regarding its sensitivity and specificity and its relation to disease activity. Also the combined RF and AKA, does it add to the diagnosis of RA. Sera from 88 consecutive RA patients, 40 disease controls and 50 healthy controls were tested for RF with latex agglutination and AKA with indirect immunofluorescence assay that used rat esophagus as a substrate. The proportion of RA patients who had AKA [49/88] was higher than in healthy controls 4/50 [X[2]=28.6, p<0.001], and in disease controls 5/40 [X[2] =19.2, p<0.001]. AKA gives weaker sensitivity than RF [55.7%], but stronger specificity [87.5% versus other rheumatic, and 92% versus healthy controls]. The frequency of AKA positivity was higher among patients who had severe disease [being positive in 41/50 of active RA patients], this gives a highly significant association p<0.001. Also, AKA shows significant positive association with RF+ve results [45/71]. Combined results of both AKA and RF gave overall best results as both positive results gave a sensitivity of 97.7%, and both negative results gave a specificity of 97.5% versus rheumatic and 98% versus healthy controls. AKA adds a valuable diagnostic tool in the diagnosis of RA. It is more specific than RF. Its positivity is associated with active RA disease. Combined AKA and RF measurement gives the best sensitivity and specificity for diagnosing rheumatoid disease than each test individually