Abstract :
Detection of Antinuclear antibody (ANA) is the hallmark of laboratory investigations in Connective Tissue Disorders (CTD). However, various methodologies used in both screening tests and specific antibody detection has led to a loss of consensus and poor reproducibility of results. The objective of this study is to compare Solid Phase Immunoassay (SPI) with Indirect Immunofluorescence (IFA) as a screening test in correlation with the clinical profile as well as subsequent detection of specific antibodies. The study was conducted as a pilot study with a sample size of 60 cases, recruited by Rheumatologists, between April 2019 to July 2019. Each sample was screened by IFA and SPI and tested for specific antibodies by three different specific antibody tests. Although the Sensitivity of SPI (71%) was lower when compared to IFA (79%), the Specificity (78%), Positive Predictive Value (PPV) (74%) and Negative Predictive Value (NPV) (76%) were all comparatively higher. In two clinically proven cases of Sjogren’s syndrome where IFA was negative and SPI was positive, specific antibody tests showed positivity for SSA/Ro. Also it was seen in two clinically confirmed cases of Systemic Lupus Erythematosus IFA was positive and SPI was negative. In this pilot study SPI appeared comparable to IFA as a screening test with better specificity, PPV and NPV. The utility of SPI was especially seen in cases with antibodies against SSA/Ro where IFA may be negative. However, in a few cases of high antibody titer SPI appeared to give a false negative result.
Keyword :
Antinuclear antibody, Indirect Immunofluorescence, Solid Phase Immunoassay