IgG Avidity in Samples Collected on Filter Paper: Importance of The Early Diagnosis of Congenital Toxoplasmosis

Souza, Jéssica Yonara de; Gomes, Taynara Cristina; Rezende, Hanstter Hallison Alves; Storchilo, Heloisa Ribeiro; Rodrigues, Patrícia Giffron; Castro, Ana Maria de

doi:10.1055/s-0041-1740272

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Revista Brasileira de Ginecologia e Obstetrícia

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Sumário

Original Article, Gynecological Endocrinology • Rev Bras Ginecol Obstet. 43 (12) • Oct 2021 • https://doi.org/10.1055/s-0041-1740272 copy

IgG Avidity in Samples Collected on Filter Paper: Importance of The Early Diagnosis of Congenital Toxoplasmosis

Avidez de IgG em amostras coletadas em papel filtro: Importância no diagnóstico precoce da toxoplasmose congênita

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Objective

The purpose of the present study is to standardize and evaluate the use of the immunoglobulin G (IgG) antibody avidity test on blood samples from newborns collected on filter paper to perform the heel test aiming at its implementation in ongoing programs.

Methods

Blood samples from newborns were collected on filter paper simultaneously with the heel prick test. All samples were subjected to immunoglobulin M IgM and IgG enzyme-linked immunosorbent assays (ELISA). Peripheral blood was collected again in the traditional way and on filter paper from newborns with high IgG levels (³3). Three types of techniques were performed, the standard for measuring IgG in serum, adapted for filter paper and the technique of IgG avidity in serum and on filter paper. The results of the avidity test were classified according to the Rahbari protocol.

Results

Among the 177 samples, 17 were collected in duplicate from the same child, 1 of peripheral blood and 1 on filter paper. In this analysis, 1 (5.88%) of the 17 samples collected in duplicate also exhibited low IgG avidity, suggesting congenital infection. In addition, the results obtained from serum and filter paper were in agreement, that is, 16 (94.12%) samples presented high avidity, with 100% agreement between the results obtained from serum and from filter paper.

Conclusion

The results of the present study indicate that the avidity test may be another valuable method for the diagnosis of congenital toxoplasmosis in newborns.

Keywords
toxoplasmosis; IgG avidity; filter paper; neonatal screening; pregnancy

Standard technique to measure serum IgG levels	Technique adapted to measure IgG levels on filter paper	Technique to determine IgG avidity in serum and on filter paper
100 μl of sample diluent + 5 μl of sample	Perforation with specific 5mm diameter perforator + 10 μl of sample diluent	Serum: 100 μl of sample diluent + 5 μl of sample Filter paper: 100 μl of sample diluent + one 5mm diameter filter paper disc
Incubation for 30 minutes at 37°C	Incubation for 30 minutes at 37°C	Incubation for 30 minutes at 37°C
First wash with 300 μl of washing solution previously prepared according to the manufacturer’s instructions	Removal of filter papers and first wash with 300 μl of washing solution previously prepared according to the manufacturer’s instructions	First wash with 300 μl of previously prepared solution of 6M Urea
	Addition of 100 μl of conjugate Incubation for 30 minutes at 37°C Second wash with 300 μl of washing solution previously prepared according to the manufacturer’s instructions Addition of 50 μl of substrate A and 50 μl of substrate B Incubation for 10 minutes at 37°C Addition of 50 μl of stop solution Reading on filters at 450nm and 630nm

Results	Mother		Child
	Absolute number	%	Absolute number	%
Reagent (IgM)	0	0	0	0
Reagent (IgG)	167	94.36	167	94.36
Reactive mother and non-reactive child (IgG)	5	2.82	5	2.82
Non-reactive mother and child (IgG)	5	2,82	5	2,82
Total samples	177	100	177	100

Samples	IgG avidity serum	IgG avidity filter paper	IgG serum (ELISA index)	IgG filter paper (ELISA index)
Patient 1	26%	26%	3.52	3.31
Patient2	52%	56%	2.94	2.75
Patient3	48%	43%	2.65	2.37
Patient4	89%	89%	2.04	1.47
Patient5	61%	87%	1.51	1.71
Patient6	56%	73%	2.0	2.02
Patient7	87%	86%	1.27	0.99
Patient8	95%	77%	16.70	17.21
Patient9	76%	84%	1.24	1.56
Patient10	77%	88%	3.72	2.59
Patient11	81%	91%	5.13	4.60
Patient12	86%	73%	3.44	4.53
Patient13	52%	55%	3.86	3.54
Patient14	72%	81%	2.25	2.18
Patient15	94%	92%	1.88	1.83
Patient16	53%	99%	4.72	2.17
Patient17	52%	55%	3.86	3.54

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[1] Address for correspondence Jéssica Yonara de Souza, 235th Street, Setor Universitário, 74605-050, Goiânia, State of Goiás, Brazil (e-mail: jessica_yonara@hotmail.com).