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Home arrow Economics arrow American Trypanosomiasis Chagas Disease, Second Edition: One Hundred Years of Research

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Tests in the chronic phase

Application of tests in the situations that follow are always serological for routine purposes. Parasitological tests are performed only for research.

Confirmation of a clinical case

The most common situation is the confirmation or exclusion in a particular case. This case may arrive at the clinician by several channels: (1) an outpatient consultation as a routine checkup; (2) from a blood bank because of exclusion as a donor; (3) during a selection for a job in a country in which screening for T. cruzi is mandatory and an infection was found; (4) patient has relatives with Chagas and wants to exclude/confirm the infection; and (5) a gynecologist may send the pregnant patient for evaluation of risk to have the infection and then to investigate for congenital transmission.

In any case, the physician should look for symptoms and signs common in Chagas disease, ask for epidemiological background (an infected mother is important), and ask for laboratory tests for confirmation or exclusion. These serological tests should be very specific and performed in parallel, with at least two tests of different principles (i.e., ELISA and HA; IFI and HA, recombinant ELISA and HA). The results should be expressed in titers for IFI, HA, and OD of the sample and of the cutoff of the plate for ELISA, together with a table with the normal values for the population of the region. If results demonstrate anti-T. cruzi antibodies in high titers in both tests, the chances of error are minimized.

The serological confirmation of T. cruzi infection ought to be done with two tests of different principles. A common mistake made by the clinicians is to accept the result of a single rapid test or a single recombinant ELISA result or a single chemiluminiscence result (i.e., CMIA Architect). Rapid tests lack the specificity and sensitivity necessary to make or exclude the serological diagnosis.97 The single recombinant ELISA and the single chemiluminiscence tests have a very high sensitivity, but not the required specificity to assure diagnosis; false positives may be found. A second assay will confirm or exclude the infection. If results are discordant (one positive, the other negative) a detailed search of the true situation is necessary.

An error at this stage may have legal consequences. A false-negative result may lead the physician to look for other diseases or believe the patient is noninfected. Perhaps a false positive may be even worse, because he/she will have the stigma of a severe disease that may be fatal. This person may even have had relatives dead from Chagas disease.

 
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