Arq. Bras. Cardiol. 2020; 115(6): 1092-1093
Serological Tests in Chagas Disease: Another Enigmatic Evidence in a Disease Largely Neglected
André Schmidt
, José Antonio Marin Neto
This Short Editorial is referred by the Research article "Prevalence of Trypanosoma Cruzi Infection in Blood Donors".
Cardiologists and Gastroenterologists acting in distinct environments of our institution in Ribeirão Preto, not infrequently face patients with epidemiologic, clinical and laboratorial features of Chagas Disease (CD) in whom serological evaluation is negative for the disease. In a series of 65 patients evaluated between 07/01/2011 and 12/31/2012 by invasive coronary angiography to elucidate the cardinal symptom of chest pain, all with wall motion abnormalities (including 28 presenting the typical apical aneurysm at contrast ventriculography), two distinct serological tests were positive in only 11(17%) patients. How can we elucidate this enigma and provide guidance in this situation? The answer may be, in part, in the experience with this entity and in the knowledge and confidence in the diagnostic accuracy of the serological tests employed.
The hitch point begins with the asymmetrical concepts leading to uncertainty that involve the routine diagnostic procedures of CD by using serological verification of antiparasite antibodies. In accordance to current guidelines, , only one negative test is enough to exclude the diagnosis (granting blood donation or solid organ transplantation), while two distinct positive serological tests are needed to confirm CD diagnosis. This is an ancient practice in clinical and research routines, due to the heterogeneous accuracy (mean of sensibility and specificity) of the tests/ e. g. complement fixation, indirect hemagglutination, indirect immunofluorescence and direct agglutination).Even after the development of chemiluminescence methods based on ELISA, capable of automated reading to avoid subjective interpretation as seen in the above-mentioned tests, the rule of two simultaneous distinct tests followed by a third one if a discordant result is obtained, remains in the latest PAHO guidelines for diagnosis of CD.A conflicting technical note from the WHO recommended a single ELISA test for screening in blood banks, supported by its alleged high sensitivity (nearly 99%) and as a way of cost reduction when dealing with a high volume of screening as occurs in blood centers and blood banks.Nevertheless, well-documented evidence exists suggesting that this protocol may not be entirely adequate.
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