Proportion of Patients with Negative Nuclear Pattern by Antinuclear Antibody Test and Characteristics of Specific Antibodies Detected

Abstract

Autoantibodies might be undetected in some autoimmune-suspected patients, by both antinuclear antibodies (ANAs) screening test and specific antibodies detection. This work aimed to evaluate the proportion of negative ANA nuclear results and to study the detection rates and types of specific antibodies detected, along with the clinical diagnosis of these patients. The laboratory records of patients in Khon Kaen Hospital who were suspected of autoimmune rheumatic diseases (ARDs) by clinicians and underwent ANA test using indirect immunofluorescence assay (IFA) and specific antibody detection by line immunoblot assay (LIA) were reviewed. The retrospective data were collected and investigated from 2017–2020 and the patients with negative ANA nuclear pattern were selected for analysis of clinical diagnosis. The data were analyzed using descriptive statistics, chi-square test or Fisher's exact test. Out of 1,002 cases of serum samples, 127 (12.7%) were found with negative nuclear pattern of ANA. In this group, positive cytoplasmic staining patterns could suggest the tendency of specific antibodies detection (P<0.001), that is, from 16.5% (21/127) positive cases, 61.9% (13/21) were found with specific antibodies, while the remaining 83.5% (106/127) negative cases only 14.2% (15/106) were detected. This is also true for the tendency of diagnosis as ARD (P=0.001), that is, the positive cytoplasmic cases were diagnosed as ARD by 71.4% (15/21), compared to only 32.1% (34/106) for the negative cases. However, positive mitotic staining patterns could not suggest such tendencies. When at least one cytoplasmic pattern was positive, detection of specific antibodies led to higher proportion of ARD diagnosis, i.e., from 71.4% (15/21) with only ANA considered to 92.3% (12/13) when specific antibodies were also detected. The most frequent specific antibodies detected were anti-Ro52 (73.3%; 11/15) and anti-SSA (40.0%; 6/15), mostly with high intensity. In contrast, when cytoplasmic patterns were negative, proportions of ARD were similar whether specific antibodies were detected or not, i.e., 33.3% (5/15) when detected, and 31.9% (29/91) when not, suggesting that specific antibodies detection could not distinguish between ARD and non-ARD clearly in this case. Additionally, intensity of specific antibodies found in non-ARD was likely low. The most frequently found disease in patients with negative nuclear pattern of ANA was SLE. The investigation suggested that positive cytoplasmic patterns together with specific antibodies detection were more likely to lead to SLE diagnosis than in the other groups (30.8%; 4/13). However, cases of SLE were too few to be statistically concluded. In conclusion, when the result of ANA screening test is negative for nuclear patterns, positive cytoplasmic patterns can help suggest ARD when combined with specific antibodies detection. Patient clinical symptoms should also be considered altogether.