Abstract
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. Prospective, double-blind study at the parasitology laboratory of Faculdade de Medicina da Fundação ABC. 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 ++++). 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). 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.
Highlights
Giardiasis is common worldwide, and 10% to 15% of the population is infected, even in first-world countries.[1]
The enzyme-linked immunosorbent assay (ELISA) test was positive even when a significant proportion of corresponding samples examined by microscopy were negative
The ELISA test is useful when just searching for Giardia lamblia, because of its high sensitivity
Summary
Giardiasis is common worldwide, and 10% to 15% of the population is infected, even in first-world countries.[1]. The 65-kDa Giardia-specific antigen 65 (GSA 65) glycoprotein was considered to be the antigen of interest It is present in the cysts and trophozoites of Giardia lamblia and is very specific to this parasite. It is the main antigen found in the feces of individuals infected with Giardia lamblia, and it has been used for immunodiagnosis.[15] The earliest immunoenzymatic assays performed showed sensitivity of 92% and specificity of 98%, with the inconveniencing factor that they needed to be performed using fresh stools.[16] In 1989, it became possible to apply specific antigens against the Giardia lamblia cyst wall, such as GSA 65, and this increased the sensitivity from 96% to 99% and the specificity from 96% to 100%.17. The limiting factor in using this technology is its high cost in comparison with traditional microscopy methods
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