False-Positive HIV Screening in New-Onset Systemic Lupus Erythematosus Presenting with Polyserositis and Lupus Nephritis.

False-reactive human immunodeficiency virus (HIV) screening can occur in systemic lupus erythematosus (SLE) and may delay recognition of the underlying autoimmune disease. A 23-year-old woman presented with weight loss, polyserositis and nephrotic-range proteinuria. Her HIV antigen/antibody screen was reactive, but supplemental testing did not confirm HIV infection. Lupus serologies, hypocomplementemia and kidney biopsy established SLE with mixed proliferative and membranous lupus nephritis. Recurrent pleural and progressive pericardial effusions required immunosuppression, pericardial drainage, a surgical window and pleural decortication. The reactive HIV screen initially favoured an infectious diagnosis; however, proteinuria, haematuria and low complement levels suggested immune-complex disease. This illustrates the risk of diagnostic anchoring on a preliminary screening result. A reactive HIV screen is not diagnostic. Prompt supplemental testing and parallel evaluation for autoimmune disease can prevent delayed diagnosis of SLE. LEARNING POINTS: A reactive HIV screening assay is preliminary, not diagnostic; in patients with autoimmune features, prompt supplemental testing is essential because systemic lupus erythematosus can cause false reactivity.A reactive HIV screen may create diagnostic anchoring when weight loss, serosal effusions and renal abnormalities coexist; discordant clinical and laboratory findings should trigger reassessment rather than premature attribution to HIV.In a young patient with unexplained polyserositis, proteinuria and glomerular haematuria, early lupus serology, complement testing and careful family history can expedite the diagnosis of severe lupus nephritis.