Evaluation of Three Point-of-Care Tests for Detection of Toxoplasma Immunoglobulin IgG and IgM in the United States: Proof of Concept and Challenges.

Abstract

BackgroundThe cost of conventional serological testing for toxoplasmosis discourages universal adoption of prenatal monthly screening programs to prevent congenital toxoplasmosis. Point-of-care (POC) technology may constitute a cost-effective approach.MethodsWe evaluated the diagnostic accuracy of 3 Toxoplasma POC tests against gold-standard testing performed at Palo Alto Medical Foundation Toxoplasma Serology Laboratory (PAMF-TSL). The POC tests included the following: Toxo IgG/IgM Rapid Test (Biopanda) and the OnSite Toxo IgG/IgM Combo-Rapid-test that detect IgG and IgM separately, and the Toxoplasma ICT-IgG-IgM-bk (LDBIO) that detects either or both immunoglobulin IgG/IgM in combination. Samples were selected from PAMF-TSL biobank (n = 210) and Centers for Disease Control and Prevention Toxoplasma 1998 Human Serum Panel (n = 100). Based on PAMF-TSL testing, Toxoplasma-infection status was classified in 4 categories: acute infections (n = 85), chronic infections (n = 85), false-positive Toxoplasma IgM (n = 60), and seronegative (n = 80). The POC testing was performed in duplicate following manufacturer’s instructions by investigators blinded to PAMF-TSL results. Sensitivity and specificity were calculated.ResultsA total of 1860 POC tests were performed. For detection of Toxoplasma IgG, sensitivity was 100% (170 of 170; 95% confidence interval [CI], 97.8%–100%) for all 3 POC kits; specificity was also comparable at 96.3% (77 of 80; 95% CI, 89.5%–98.9%), 97.5% (78 of 80; 95% CI, 91.3%–99.6%), and 98.8% (79 of 80; 95% CI, 93.2%–99.9%). However, sensitivity for detection of Toxoplasma IgM varied significantly across POC tests: Biopanda, 62.2% (51 of 82; 95% CI, 51.4%–71.9%); OnSite, 28% (23 of 82; 95% CI, 19.5%–38.6%); and LDBIO combined IgG/IgM, 100% (82 of 82; 95% CI, 95.5%–100%). Diagnostic accuracy was significantly higher for the LDBIO POC kit. The POC kits did not exhibit cross-reactivity for false-positive Toxoplasma-IgM sera.ConclusionsThe 3 evaluated POC kits revealed optimal sensitivity for Toxoplasma-IgG antibodies. The LDBIO-POC test exhibited 100% sensitivity for the combined detection of IgG/IgM in acute and chronic Toxoplasma infection. Biopanda and Onsite POC tests exhibited poor sensitivity for Toxoplasma-IgM detection.