title: [Standardization of a direct agglutination test for the immunodiagnosis of Chagas disease].
abstract: BACKGROUND
  Chagas' disease is caused by the parasite Trypanosoma cruzi and its immunological diagnosis is mainly based on the detection of antibodies against T. cruzi using tests such as the ELISA, the indirect fluorescence antibody test (IFAT) and the indirect hemagglutination test (IHAT). The main disadvantage of the IHAT is the need to prepare sheep erythrocytes, whose availability is limited and they have a short duration once prepared. However, there are alternative tests, such as the direct agglutination test (DAT).
  
  
  OBJECTIVE
  To standardize the direct agglutination test for the diagnosis of Chagas disease.
  
  
  METHODS
  Trypanosoma cruzi epimastigotes were prepared using two protocols, with and without trypsin treatment. The parasites were stained and optimal conditions for parasitic concentration and serum dilutions were determined. We evaluated the technique using sera from patients with Chagas disease, from healthy individuals and from individuals with other parasitic diseases.
  
  
  RESULTS
  The optimal parasitic concentration was 500 x 10(6) parasites/ml using stained parasites without trypsin treatment. The optimal serum dilutions were 1/25, 1/50 y 1/100 and the cut-off point was the 1/50 dilution. The diagnostic indices for the standardized technique were as follows: Sensitivity, 94.3% (95% CI: 79.5-99.0) and specificity, 96.3% (95% CI: 88.8-99.0), with positive and negative predictive values of 91.7% (95% CI: 76.4-97.8) and 97.5% (95% CI: 90.4-99.6), respectively. Cross-reaction was observed only in three sera from individuals with visceral leishmaniasis. The results were compared with those obtained by IHA, ELISA, and IFA, and the concordance rate was 96% and the kappa index, 0.90 (95% CI: 0.81-0.99).
  
  
  CONCLUSIONS
  The standardized direct agglutination test could be useful for immunodiagnosis of Chagas disease.
authors: Departamento Clínico Integral, Facultad de Ciencias de la Salud, Universidad de Carabobo, Maracay, Venezuela.
authors: Yenny
authors: Y
authors: Alviarez
authors: Instituto de Investigaciones Biomédicas Dr. Francisco J. Triana-Alonso, Universidad de Carabobo, Maracay, Venezuela.
authors: María
authors: M
authors: Lares
authors: Instituto de Investigaciones Biomédicas Dr. Francisco J. Triana-Alonso, Universidad de Carabobo, Maracay, Venezuela.
authors: Mercedes
authors: M
authors: Viettri
authors: Centro de Investigaciones en Enfermedades Tropicales, Facultad de Ciencias de la Salud, Universidad de Carabobo, San Carlos, Venezuela.
authors: Cruz M
authors: CM
authors: Aguilar
authors: Instituto de Zoología y Ecología Tropical, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela.
authors: Leidi
authors: L
authors: Herrera
authors: Departamento de Parasitología, Facultad de Ciencias de la Salud, Universidad de Carabobo, Maracay, Venezuela.
authors: Elizabeth
authors: E
authors: Ferrer
mesh_terms: D000913:Antibodies, Protozoan / Q000097:blood*; D000918:Antibody Specificity; D014355:Chagas Disease / Q000175:diagnosis*; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D005188:False Negative Reactions; D005189:False Positive Reactions; D019084:Fluorescent Antibody Technique, Indirect; D006386:Hemagglutination Tests / Q000592:standards*; D006801:Humans; D007893:Leishmania donovani / Q000276:immunology; D059208:Parasite Load; D018512:Parasitemia / Q000175:diagnosis*; D010272:Parasitic Diseases / Q000175:diagnosis; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014349:Trypanosoma cruzi / Q000276:immunology*
chemical_list: D000913:Antibodies, Protozoan