The role of laboratory investigations in evaluating abdominal tuberculosis

Tuberculosis (TB) continues to be a major health problem in developing countries like India. Abdominal TB is defined as an infection of the peritoneum, or hollow or solid abdominal organs with Mycobacterium tuberculosis (Mtb). The gastrointestinal tract is one of the most frequent sites of extrapulmonary involvement in TB. The present study was undertaken to evaluate the role of laboratory investigations in the diagnosis of abdominal TB.

The study was conducted on 300 patients admitted to various departments of our hospital from November 2005 to October 2007. Detailed histories and thorough clinical examinations together with relevant hematological, biochemical, cytological, radiological, and histopathological investigations were carried out in suspected cases of Koch's abdomen.

Erythrocyte sedimentation rates with positive results were seen in 79.3% patients. Serological test enzyme-linked immunosorbent assay was performed on only 30 patients and was found to be positive for IgG, and IgM in 25 cases with a sensitivity of 83%. Thirteen out of 15 cases were positive for adenosine deaminase done on ascitic fluid. The results of the two patients who underwent Mtb polymerase chain reaction (PCR) were consistent with TB. Out of 21 image-guided fine-needle aspiration cytology (FNAC) cases, 10 (48%) of the positive cases showed caseating necrosis while 7 (33%) had noncaseous necrosis. Stain for acid-fast bacilli (AFB) was performed on all cases and was positive in 42 cases (38.8%). Lymph node biopsy was done in 95% of the cases.

Serological investigations have a limited value, while PCR is a highly specific test. Since cost restricts its use, only two patients in our study could afford it. BACTEC is more sensitive and faster than culture techniques for the diagnosis of mycobacterial infections. FNAC is a reliable, cost effective alternative, and 81% diagnostic yield in the present study suggests that ultrasound guidance is a useful tool. Histopathological evaluation with positive AFB staining remains the gold standard for diagnosing abdominal TB. However, although the demonstration of AFB in aspirates and tissue sections is a definitive diagnostic method for TB, the positivity for AFB is variable.