Detection by Enzyme Immunosorbent Assay of Toxoplasma gondii IgG Antibodies in Dried Blood Spots on PKU-filter Paper from Newborns

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Abstract
Different ways of eluting IgG antibodies against Toxoplasma gondii from blood spots on PKU filter papers from newborns were examined, and the eluate was analysed by Enzyme Immunosorbent Assay (EIA). 10-mm diameter discs (method A), and 3-mm discs (method B) were eluted overnight, and 3-mm discs were eluted directly for 2 hours in the EIA wells (method C). Two groups of paired samples were tested: blood spots on the PKU card from the newborn, cord blood, and a venous blood sample from the mother collected shortly after delivery (Group 1, 191 samples); or PKU cards from the newborns and serum collected from the mother during the first trimester (Group 2, 426 samples). The best results were found for Group 1; method A, a sensitivity of 100% (63/63), and a specificity of 100% (128/128) (r = 0.934, P < 0.0001), and for Group 2; method C, a sensitivity of 100% (125/125), and a specificity of 100% (301/301) (r = 0.822, P < 0.0001). When method C, was used on 188 samples stored for 16-18 month at -20 degrees C, a sensitivity of 100% (62/62) and a specificity of 99.2% (125/126) (r = 0.913, P < 0.0001) were found. The PKU filter paper method is reliable and reproducible, and can be used in screening projects based on analysis of neonatal samples, and in epidemiological studies on toxoplasmosis in pregnant women.