title: The impact of lowering the cut-off value on the sensitivity of the Platelia Elisa IgG (Bio-Rad) test for toxoplasmosis diagnosis.
abstract: Determining specific immune status against Toxoplasma gondii is essential for assessing the risk of reactivation in immunocompromised patients or defining serological monitoring and appropriate prophylactic measures during pregnancy. In France, toxoplasmosis serological screening requires systematic testing for IgM and IgG antibodies. The Platelia Toxo IgG and IgM test (Bio-Rad) is one of the most widely used tests for anti-toxoplasmic antibody detection. We performed a study on 384 sera, including 123 IgG negative (<6 IU/mL) and 261 IgG equivocal (6-9 IU/mL) sera tested with Platelia Toxo IgG and collected during routine screening at Pitié-Salpêtrière Hospital, Paris, France to determine the best-performing IgG titer cut-off value. Out of these 383 sera, 298 were IgM negative by Platelia Toxo IgM and 86 were IgM positive. All sera were also tested against Toxo IgG II LD BIO western blot test as confirmation. Our results indicated that an IgG titer cut-off value of ≥4.4 IU/mL for the Platelia Toxo IgG met the definition of positivity, a value significantly lower than that indicated by the manufacturers. In the presence of IgM antibodies, the IgG titer cut-off decreased significantly to a value ≥0.2 IU/mL. This latter cut-off also allowed adequate diagnosis of proven toxoplasmosis seroconversion in 76.7% of cases (33/43). Our findings may improve toxoplasmosis care by reducing therapeutic intervention time and eliminating the need for further serological monitoring.
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France.
authors.forename: Oussama
authors.initials: O
authors.lastname: Mouri
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Kendjo
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France.
authors.forename: Feriel
authors.initials: F
authors.lastname: Touafek
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France - Centre d'Immunologie et des Maladies Infectieuses, CIMI-Paris, 75013 Paris, France - Sorbonne Universités, UPMC Université Paris 6, CIMI-Paris, 75005 Paris, France.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Fekkar
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France.
authors.forename: Ousmane
authors.initials: O
authors.lastname: Konte
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France.
authors.forename: Sebastien
authors.initials: S
authors.lastname: Imbert
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Courtin
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France - Centre d'Immunologie et des Maladies Infectieuses, CIMI-Paris, 75013 Paris, France - Sorbonne Universités, UPMC Université Paris 6, CIMI-Paris, 75005 Paris, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Mazier
authors.affiliation: AP-HP, Groupe Hospitalier La Pitié-Salpêtrière, Service de Parasitologie-Mycologie, 75013 Paris, France.
authors.forename: Luc
authors.initials: L
authors.lastname: Paris
mesh_terms: D000328:Adult; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D015153:Blotting, Western; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000592:standards*; D005260:Female; D005602:France; D006801:Humans; D016867:Immunocompromised Host; D007074:Immunoglobulin G / Q000097:blood*; D007075:Immunoglobulin M / Q000097:blood; D008403:Mass Screening; D011247:Pregnancy; D015597:Pregnancy Complications, Parasitic / Q000175:diagnosis; D012372:ROC Curve; D012015:Reference Standards; D012680:Sensitivity and Specificity; D000069078:Seroconversion; D014122:Toxoplasma / Q000276:immunology*; D014123:Toxoplasmosis / Q000175:diagnosis*
chemical_list: D000913:Antibodies, Protozoan; D007074:Immunoglobulin G; D007075:Immunoglobulin M