From the Guidelines
Laboratory testing for Chagas disease should primarily involve serological tests, such as enzyme-linked immunosorbent assay (ELISA), for initial screening, particularly in the latent and chronic stages of infection, as recommended by the Infectious Diseases Society of America and the American Society for Microbiology 1.
Diagnostic Approach
The diagnostic approach for Chagas disease varies depending on the stage of infection.
- In the acute phase, which lasts about 4-8 weeks, microscopy of Giemsa-stained thick and thin blood or buffy coat films is the standard method for diagnosis, as extracellular trypanosomes are present during this time 1.
- However, infection is rarely diagnosed in the acute stage, as only 1%–2% of infected individuals present with symptoms during this time period 1.
Serological Testing
- Serology by commercially available ELISA kits is of greatest use during the latent and chronic stages of disease when parasites are no longer easily detected in peripheral blood preparations by microscopy 1.
- Positive ELISA results are considered evidence of active infection and would exclude potential blood/tissue donors who test positive from acting as donors, as the infection has been shown to be transmitted by transfusion and transplantation 1.
Other Diagnostic Methods
- Microscopic examination of tissue aspirates/biopsies by Giemsa/H&E stains, culture in NNN or other suitable media, and nucleic acid amplification tests (NAAT) are also available for diagnosis, but their use depends on the stage of infection and the availability of resources 1.
Importance of Early Diagnosis
Early diagnosis of Chagas disease is crucial, as antiparasitic treatment is most effective in acute or early chronic phases before irreversible organ damage occurs 1.
- The treatment typically involves benznidazole 5-7 mg/kg/day or nifurtimox 8-10 mg/kg/day, both divided into two daily doses for 60 days 1.
High-Risk Groups
Testing is particularly important for individuals from endemic areas, those with potential maternal transmission, recipients of blood transfusions or organ transplants from endemic regions, and those with clinical manifestations suggesting Chagas disease, such as cardiac abnormalities 1.
From the Research
Laboratory Testing for Chagas Disease
- Chagas disease is a major public health issue, and laboratory testing is crucial for its diagnosis and treatment monitoring 2, 3.
- The disease can be diagnosed by three kinds of techniques: direct, indirect, and molecular, with indirect techniques being recommended for chronic undetermined phase and symptomatic phase 4.
- Indirect techniques, such as immunoassay techniques (ELISA), detect IgG antibodies directed against T. cruzi antigens, but false positive results are possible, and a positive or undetermined result must be confirmed by at least another technique 4.
- Rapid diagnostic tests (RDTs) have shown versatility in detecting chronic Trypanosoma cruzi infections, with a performance equivalent to that of conventional tools, and can provide results within an hour without requiring cold storage 5.
- In the United States, diagnosis in the chronic phase requires positive results from two different IgG serological tests, with three enzyme-linked immunosorbent assays (ELISAs) and one rapid test being FDA cleared 6.
- The performance of these tests varies, with InBios having the highest sensitivity but the lowest specificity, and Hemagen having the lowest sensitivity but high specificity 6.
- The level of antibody reactivity and clinical sensitivity can also vary depending on the region of origin, with donors from Mexico having the lowest levels, followed by those from Central America, and then those from South America 6.
Serological Testing
- Serological testing is a crucial component of Chagas disease diagnosis, with ELISA being a commonly used technique 2, 4, 6.
- However, serological testing can have limitations, such as false positive results, and requires confirmation by at least another technique 4.
- The use of a high-sensitivity screening test followed by a high-specificity confirmatory test can improve laboratory diagnosis of Chagas disease 6.
Molecular Testing
- Molecular testing can detect parasite genetic material and can be used to make the diagnosis in acute or chronic phase of infection, with more accuracy in the acute phase 4.
- Molecular testing is mainly recommended to diagnose vertical transmission of T. cruzi, as early diagnosis of congenital infection increases the possibility to cure the sibling, and it is a good marker to evaluate the effectiveness of treatment 4.