Diagnostic utility of unidentified precipitin line (UPL)

Abstract

<h3>Background</h3> Unidentified precipitin line (UPL) is a line which does not characterise with known ENA antibodies. Currently, the clinical significance of UPL is uncertain. <h3>Aim</h3> The aim of this study was to determine clinical and laboratory correlation of UPL detected over a 3 year period in Flinders Medical Centre Immunopathology Laboratory. <h3>Method</h3> Retrospective analysis of 144 patients with UPL on ENA testing. <h3>Results/Discussion</h3> ENA and their characterisation were performed on 11,869 occasions with 1.21% demonstrating UPL. The majority of patients with UPL are female (71%) and average age is 60 years. Precipitin lines for both K562 and RTE were more frequent (47%), compared to K562 only (41%), and RTE only (12%). The most common ANA pattern is speckled (29%), homogenous (16%), mixed patterns (14%), with 30% negative ANA. Both ANA positive and ANA negative patients with UPL are associated with connective tissue and autoimmune disease with the majority demonstrating an association of UPL with Ro52 and/or SSA. UPLs were also identified in renal disease, pulmonary fibrosis/bronchiectasis and malignancy. <h3>Conclusion</h3> UPL can be found in the absence of a positive ANA and its presence in autoimmune disease strongly suggests that it has clinical utility.