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Indian Journal of Pathology: Research and Practice

Volume  4, Issue 1, Jan-Jun 2015, Pages 21-26
 

Original Article

IGRA Assay Diagnostic Performance in Extra Pulmonary TB and Comparison with Serum ADA and TST

Sodani Sadhna*, Hawaldar Ranjana**

*Assistant Professor, Microbiology Deptt., MGM Medical college, Indore. **Microbiology Deptt., Sampurna Sodani Diagnostic Clinic, Indore (M.P).

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DOI: DOI : https://dx.doi.org/10.21088/ijprp.2278.148X.4115.4

Abstract
Background : TB (Tuberculosis )is the second most common cause of death from infectious diseases worldwide. Every year TB claims the lives of about 3 million people and newly infects 8million people more throughout the world. India alone accounts for 2 million active TB cases and 0.5 million deaths per  year. The enormous pool of latently infected individuals poses a major hurdle for global TB control. Each person carrying latent TB infection ( LTBI) has approximately a 10% chance of progressing to active disease. The rate of progression is elevated among certain groups including those who have been recently infected and those with a weakened immune response. Making the diagnosis of LTBI is constrained by low bacterial load that makes it impossible to directly detect Mycobacterium tuberculosis and a weak humoral response that makes serological testing unreliable. With the banning of TB IgG and IgM Test methodologies by WHO a few years back  due to false results there was a need for a serological test for diagnosing  extrapulmonary TB where no other site specific sample is available for PCR or culture. Recently interferon gamma release assays( IGRA) have shown their superior diagnostic performance over TST and ADA by using atleast two superior antigens ,Early secretory antigentarget 6(ESAT-6 )and culture filtrate protein-10(CFP-10 )present exclusively in Mycobacterium  tuberculosis but absent in BCG strains and most non tuberculous mycobacteria[5].  It is a whole blood test that can aid in diagnosing Mycobacterium tuberculosis infection including both LTBI and active disease. Aim: The present study was a prospective study conducted between August 2014  to January 2015 in 110 patients coming   to Sampurna Sodani Diagnostic Clinic Microbiology department, a stand alone diagnostic centre of Central Madhya Pradesh with suspicion of Mycobacterium tuberculosis infection. The study aims to analyse the performance of IGRA(Immunocheck Platinum assay , Immunoshop) in extra pulmonary TB cases and comparing it with serum ADA levels and TST. Materials and method: From August 2014 to January 2015, 110 patients suspected of having EPTB were included in the study. Interferon gamma release assay was performed according to manufacturer’s instructions ((Immunocheck TB, Immunoshop). A positive test was defined as T-N Value of e” 14.0 but > 25%  of N value, A negative result was defined as T-N value of < 14.0 or e” 14.0 but <25 % of N. Indeterminate results were excluded from the study.Simultaneously serum ADA was performed on all the 110 patients and ADA below 30 u/L was considered negative. Only 12 patients were advised TST by clinicians.For diagnostic puposes a TST with induration > 10 mm was considered positive. Statical analysis used: Cohen’s Kappa statistical analysis. Results: Out of 110 patients ,31 patients were positive with both IGRA(Immunocheck TB )and serum ADA. 10 patients were positive with IGRA(Immunocheck TB) but negative with serum ADA. None of the patients showed negative results withIGRA( Immunocheck TB) but positivity with serum ADA. 69 patients were negative with bothIGRA( Immunocheck TB ) and serum ADA. The correlation between the two tests   was 81.26%. with K value of 0.80. Conclusion: IGRA is a new assay based on in vitro detection of IFN-Y that may replace TST as a diagnostic tool for latent and active TB especially EPTB. The tests is more specific and does not require patients to return for a second visit. Cost , technical limitations and limited data in the most vulnerable groups such as children and immuno suppressed patients may present the immediate replacement of TST.   

 Keywords: IGRA; Immunocheck TB;TST; Serum ADA; INF Y. 


Corresponding Author : Hawaldar Ranjana**