RESUMO
Decision analysis was used to examine the potential effect on cost and expected quality of care of the introduction of serodiagnosis by enzyme-linked immunosorbent assay (ELISA) of tuberculosis at the Instituto de Torax in La Paz, Bolivia. Previously published data collected at that facility were used as the basis for this analysis. Decision trees were constructed including test availability, test result, test predictive values, and the consequences of correct or incorrect treatment decisions. Five diagnostic algorithms were assessed. ELISA was found to make a contribution to the diagnosis of tuberculosis similar to that of sputum smear. Chest roentgenography improved the quality of patient care, but it did so at substantially increased cost. While ELISA did not add to the diagnosis when sputum smear was available, it might be of great use where sputum smear is not available.
Assuntos
Ensaio de Imunoadsorção Enzimática , Tuberculose Pulmonar/diagnóstico , Técnicas de Apoio para a Decisão , Humanos , Pulmão/diagnóstico por imagem , Valor Preditivo dos Testes , Radiografia , Sensibilidade e Especificidade , Escarro/microbiologia , Tuberculose Pulmonar/diagnóstico por imagem , Tuberculose Pulmonar/microbiologiaRESUMO
An enzyme-linked immunosorbent assay (ELISA) was evaluated as a serodiagnostic test for active tuberculosis in La Paz, Bolivia. ELISA was compared with sputum smear in 277 persons presenting to the Instituto de Torax and was used for screening in 1,458 military personnel. The test was performed under field conditions on 4-microliter samples of capillary blood obtained by finger prick. ELISA was found to have a sensitivity of 69% and a specificity of 88%. Sputum smear had a sensitivity of 79% and a specificity of 100%. ELISA was found to have undiminished sensitivity and specificity in patients who were sputum-negative, and the two tests could be combined to achieve a sensitivity of 92% and specificity of 88%. Positive and negative predictive values were highest for populations with tuberculosis prevalences in the range of that seen among patients presenting to the Instituto de Torax in Bolivia, but ELISA also led to the diagnosis of tuberculosis in 5 of 1,458 soldiers tested in the screening program.
Assuntos
Ensaio de Imunoadsorção Enzimática , Tuberculose Pulmonar/diagnóstico , Adolescente , Adulto , Bolívia , Diagnóstico Diferencial , Ensaio de Imunoadsorção Enzimática/métodos , Estudos de Avaliação como Assunto , Feminino , Humanos , Masculino , Militares , Mycobacterium tuberculosis/isolamento & purificação , Escarro/microbiologiaRESUMO
IgG antibody to Mycobacterium tuberculosis antigen 5 and tuberculin purified protein derivative (PPD) was measured, by enzyme-linked immunosorbent assay (ELISA), in serum samples from 86 patients with active pulmonary tuberculosis and 91 non-tuberculous control subjects from Santa Fé, Argentina. The geometric mean titre for the tuberculosis patients was 74.6 with antigen 5 and 99.5 with PPD. In 91 control subjects the geometric mean titres were 3.6 and 15.6 respectively. Titres were not related to tuberculin reactor status or prior BCG vaccination. At a serum dilution end-point of 1:40, ELISA with antigen 5 had a sensitivity of 81.4% and a specificity of 93.4% for tuberculosis. At 1:40, ELISA with PPD showed a sensitivity of 82.6% and a specificity of 54.9% for tuberculosis. Applied at a serum dilution of 1:40 to a hypothetical model population with a tuberculosis prevalence of 2%, ELISA using antigen 5 would correctly classify 93.2% of persons and ELISA with PPD, 55.5%. At a dilution of 1:80, accuracy is increased to 99.3% with antigen 5 and 83.3% with PPD, but sensitivity decreases to 64.0% with antigen 5 and 72.1% with PPD. Thus, antigen 5 is more accurate than PPD for the diagnosis of tuberculosis using ELISA.
Assuntos
Imunoglobulina G/análise , Mycobacterium tuberculosis/imunologia , Tuberculina/imunologia , Tuberculose Pulmonar/diagnóstico , Antígenos de Bactérias/imunologia , Argentina , Ensaio de Imunoadsorção Enzimática , HumanosRESUMO
Mycobacterium tuberculosis antigen 5 is a protein antigen limited in distribution to M. tuberculosis and M. bovis and capable of eliciting typical delayed tuberculin skin test reactions in humans. A single large batch of this antigen was purified by immunoabsorbent affinity chromatography and used to skin test patients with tuberculosis and other mycobacterial infections and healthy persons in general populations in geographic areas where nonspecific tuberculin reactivity is frequently encountered. Antigen 5 was found to be no more specific as a tuberculin antigen than PPD. If the available data are accepted, then either a disparity in antigen recognition by antibody and T lymphocytes may exist or the widely accepted hypothesis attributing nonspecific tuberculin reactivity to antigenic cross reactivity with other mycobacteria may be incorrect.