Antikeratin antibodies and antiperinuclear factor as diagnostic criteria for rheumatoid arthritis

ABSTRACT

Various auto-antibodies have been described in the serum of rheumatoid arthritis [RA] patients, such as rheumatoid factor [RF], Antiperinuclear factor [APF] and antikeratin antibodies [AKA]. The aim of this study was to evaluate the association of AKA with the activity and severity of RA. Also, to assess their diagnostic value in relation to RF and APF, as well as to determine whether measurements of these antibodies are useful to distinguish early RA from other inflammatory connective tissue disorders. One hundred and ten serum samples from connective tissue [CT] disorders patients who were diagnosed according to the American College of Rheumatology [ACR] criteria were enrolled in this study. They included 68 RA and 42 different rheumatic disorders. They were tested along with 30 serum samples from apparently healthy subjects. AKA and APF were detected with the indirect immunofluorescence [IIF] technique. RF was estimated with latex fixation test [LFT] and then titrated with Rose Waaler test [RW]. Detection of erythrocyte sedimentation rate [ESR] and C reactive protein [CRP] were used as disease activity parameters. Hands and wrists x-ray films were obtained from all RA patients for joint damage evaluation. A positive AKA test was found in 48.5% of RA patients and turned to be highly specific for RA cases [disease specificity 95.8%]. RF and APA were more sensitive than AKA in detection of RA [78% and 58.8% respectively] but less specific [83.3% and 90.2% respectively]. RF positivity [>1128] was restricted to RA but occurred only in 39.6% of sero-positive RA cases. AKA fluorescence intensity grade 2 and 3 occurred only in RA patients and in 57.5% of AKA -positive RA cases. APF titer >120 was restricted to RA and occurred in 42.5% of APF-positive RA cases. No significant differences were found between RA positive and negative cases of AKA, APF or RF as regards the age or the disease duration. While significant differences were found when positive and negative cases of AKA and RF were compared as regards the ESR, CRP and radiographic changes. A significant positive correlation was found between the degree of positivity of AKA and RF titers. Moreover, a significant positive correlation was found between the degree of positivity of AKA levels and ESR and CRP levels, and also with the radiographic changes