Determination of the accuracy and optimal cut-off point for ELISA test in the diagnosis of brucellosis in Iran

Abstract number: R2180

Hasibi M., Mortazavi H., Soudbakhsh A., Esmaeeli Djavid G., Hajiabdolbaghi M., Jafari S., Emadi H., Abouzari M.

Objectives: Brucellosis is a prevalent infectious disease in Iran and finding a reliable diagnostic method is the most challengeable problem. In this study we opted to determine an optimal diagnostic cut-off point for Elisa test in Iranian brucellosis patients.

Methods: We collected 56 confirmed cases of brucellosis (based on results of blood culture and standard agglutination test) from Department of Infectious Diseases, Imam Hospital, Tehran University of Medical Sciences. Furthermore, blood samples from 126 controls including 73 healthy controls and 53 non-brucellosis febrile patients were collected. In all of the cases and controls ELISA IgG and ELISA IgM levels were measured and compared with each other by the means of box plot graph and receiver operating characteristic (ROC) curve. The sensitivity and specificity ELISA IgG and IgM were fixed in different cut-off values and IgG and IgM levels yielding maximal sensitivity plus specificity were selected for determination of optimal cut-off point.

Results: Nineteen patients had positive blood culture for Brucella melitensis. The standard agglutination test results were 1:160 or more in 54 patients. The box plot graph indicated the high degree of dispersion for IgG and IgM data in brucellosis patients compared with non-brucellosis febrile patients and healthy controls. We observed partially overlapping for IgM but not for IgG levels between cases and controls. The area under ROC curve for discrimination between cases and healthy controls were 0.978 and 0.854 for ELISA IgG and IgM, respectively which were significantly different from 0.5 (P < 0.001). In this manner, the area under ROC curve for discrimination between cases and non-brucellosis febrile patients were 0.975 and 0.931 for ELISA IgG and IgM, respectively which again were significantly different from 0.5 (P < 0.001). After calculation of sensitivity and specificity of ELISA IgG and IgM in different cut-off values, maximal sensitivity (75%) plus specificity (100%) for ELISA IgG while maximal sensitivity of 95.7% plus specificity of 83.3% for ELISA IgM were observed by cut-off of 50 IU/ml.

Conclusion: The results of present study showed that ELISA IgG is a more accurate test than ELISA IgM in the diagnosis of brucellosis. Using a cut-off of 50 IU/ml could be optimal amount for discrimination patients from controls.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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