P0382“FALSE” POSITIVITY OF SERUM ANTI-PHOSPHOLIPASE A2 RECEPTOR ANTIBODY (ANTI-PLA2R AB) IN PATIENTS WITH NON MEMBRANOUS GLOMERULAR DISEASE

Background and Aims Phospholipase A2 receptor (PLA2R) is the major target antigen in primary membranous nephropathy (PMN) and the detection of circulating autoantibodies to PLA2R (Anti-PLA2R Ab) is a major advance in understanding this disease. In this study, we aimed to determine if Anti-PLA2R Ab serves as a specific marker for PMN in our multi-ethnic Southeast Asian cohort. Method This was a prospective cohort study of all adults with glomerular disease undergoing biopsy between 1st January 2015 and 30th June 2018. Anti-PLA2R antibody levels were quantitatively determined by IgG ELISA (Euroimmun). Results are expressed as RU/ml. We considered a value of >20RU/ml to represent a positive result, value of <14RU/ml to be negative and values between 14-20 RU/ml to be indeterminate. Results Out of the cohort of 192 patients, there were 27 patients with Membranous Nephropathy (MN), with 12 PMN and 15 with secondary MN (SMN). Secondary causes were Hepatitis (1), Malignancy (1), Lupus (13). In our analyses, 10 (83.3%) PMN pts were positive for Anti-PLA2R Ab, with 7(58.3%) strongly positive with titres >200RU/ml and 2(16.7%) negative. For SMN, the majority, 12 out of 14 patients (85.7%) tested negative and the remaining 2 (7.7%) yielded values of indeterminate levels. Of note, among the 165 patients with non membranous glomerular disease, there were 15 patients (9.1%) with indeterminate Anti-PLA2R Ab levels and 31 patients (18.9%) tested positive for Anti-PLA2R antibody, with levels >20 RU/ml. Of these 31 patients, the majority of the patients had low levels of Anti-PLA2R Ab of <50 RU/ml. However there were 5 patients who had considerably high levels of Anti-PLA2R Ab of >50 RU/ml and their characteristics are tabled below (Table 1) Conclusion Consistent with other published studies, positive Anti-PLA2R antibody levels were highly specific for PMN in our multi-ethnic Southeast Asian population and our centre has since been consistently using this test for differentiating between PMN and SMN. What is most striking in our study is that we have found high-titre Anti-PLA2R antibody positivity in non-MN patients, which has not been frequently reported in literature. The unifying feature amongst these patients appear to be the presence of arterial and arteriolar sclerosis which is usually non-specific. Though we would not normally do the Anti-PLA2R antibody test in a patient with low suspicion of MN, our study findings warrants further investigation and may indicate the limited usefulness of Anti-PLA2R antibody levels as a screening tool for glomerulonephritis.