Enzyme-linked immunosorbent assay (ELISA) immunoassaying versus microscopy: advantages and drawbacks for diagnosing giardiasis.
OBJECTIVE
Giardiasis is common in Brazil. For laboratory diagnosis, the method most utilized is microscopic examination of fecal samples, but the immunoenzymatic method is also available. The aim of this work was to verify the advantages and drawbacks of immunoassaying versus microscopy for diagnosing Giardia lamblia, when a single fecal sample is analyzed.


METHODS
Prospective, double-blind study at the parasitology laboratory of Faculdade de Medicina da Fundação ABC.


METHODS
Samples were prepared according to the traditional sedimentation (Hoffman, Pons and Janer) and Faust methods. Results were deemed positive when Giardia lamblia was found by one or both methods. The Prospect ELISA kit was used for detecting Giardia lamblia-specific antigen, in accordance with the manufacturer's instructions. Results were expressed on a visual scale as negative or positive (+, ++, +++ or ++++).


RESULTS
The ELISA test was positive even when a significant proportion of corresponding samples examined by microscopy were negative. This trend was statistically significant (p < 0.001). The overall concordance of results between the ELISA test and microscopic examination of single samples was only moderate (0.50 by kappa test).


CONCLUSIONS
The ELISA test is useful when just searching for Giardia lamblia, because of its high sensitivity. For daily practice, we recommend microscopy, which is much cheaper and can also detect other parasites. The low positivity of single samples in this method can be overcome by using three samples, as recommended by most authors.
Vidal
Alaíde Mader Braga
AM
Parasitology Laboratory, Faculdade de Medicina, Fundação ABC, Rua Dona Laura 121, CEP 09040-240 Santo André, São Paulo, Brazil. amabravi@terra.com.br
Catapani
Wilson Roberto
WR
D000818:Animals; D000953:Antigens, Protozoan / Q000032:analysis*; D016009:Chi-Square Distribution; D003365:Costs and Cost Analysis; D004311:Double-Blind Method; D004797:Enzyme-Linked Immunosorbent Assay / Q000191:economics / Q000592:standards; D005243:Feces / Q000469:parasitology*; D016829:Giardia lamblia / Q000276:immunology / Q000302:isolation & purification*; D005873:Giardiasis / Q000175:diagnosis*; D006801:Humans; D008853:Microscopy; D011446:Prospective Studies
D000953:Antigens, Protozoan