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

BACKGROUND

The 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.

METHODS

We evaluated the diagnostic accuracy of 3 POC tests against gold-standard testing performed at Palo Alto Medical Foundation Serology Laboratory (PAMF-TSL). The POC tests included the following: Toxo IgG/IgM Rapid Test (Biopanda) and the OnSite Toxo IgG/IgM Combo-Rapid- that detect IgG and IgM separately, and the Toxoplasma ICT-IgG-IgM- (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 1998 Human Serum Panel (n = 100). Based on PAMF-TSL testing, -infection status was classified in 4 categories: acute infections (n = 85), chronic infections (n = 85), false-positive 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.

RESULTS

A total of 1860 POC tests were performed. For detection of 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 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 -IgM sera.

CONCLUSIONS

The 3 evaluated POC kits revealed optimal sensitivity for -IgG antibodies. The -POC test exhibited 100% sensitivity for the combined detection of IgG/IgM in acute and chronic infection. Biopanda and Onsite POC tests exhibited poor sensitivity for -IgM detection.