Intestinal Tuberculosis

The diagnosis of intestinal TB can be difficult as it presents with nonspecific clinical and radiological features and requires high degree of suspicion for diagnosis. Abdominal TB doesn’t have specific symptoms in the beginning of the disease. It’s usually diagnosed when it progress into various complications like bleeding from ulcers or blockage of intestine by narrowing of affected intestine.

Diagnosis is confirmed by isolating the TB germ from the digestive system by either a biopsy or endoscopy. However, other supportive tests that may be done are the blood test, Mantoux test, Chest X-Ray, Abdominal X-Rays (with or without barium), scans such as ultrasound and CT scan & fluid tests.

Biopsy: Biopsy is the best way to establish the diagnosis of abdominal tuberculosis. The methods of biopsy include endoscopic GI mucosal biopsy, image-guided percutanous biopsy, endoscopic ultrasound guided biopsy, and surgical (open or laparoscopic) biopsy. The caseation necrosis in granulomas is the histologic hallmark of TB.

Blood Tests: These are nonspecific and shows raised erythrocyte sedimentation rate, low Hemoglobulin (anemia) and low protein levels (hypoalbuminemia).

Fluid Test: Tubercular fluid is tested for protein level, cell count level, ADA levels and tubercular organism and its culture report.

The tubercular ascitic fluid has protein more than 3 g/dL, with a total cell count of 150-4000/μL and consists predominantly of lymphocytes. The ascitic fluid to blood glucose ratio is less than 0.96 and serum ascitic albumin gradient is less than 1.1 g/dL. The yield of organisms on smear and culture is low. Staining for acid fast bacilli is positive in less than 3% of cases and a positive culture is seen in only 20% of cases. Ascitic fluid adenosine deaminase (ADA) levels are elevated in tubercular ascites. Serum ADA level above 54 U/L, ascitic fluid ADA level above 36 U/L and an ascitic fluid to serum ADA ratio more than 0.98 are suggestive of tuberculosis. However, in cases of co-infection with HIV, ascitic ADA levels can be normal or low. Also, falsely high values can be seen in malignant ascites. Interferon-γ levels are also elevated in tubercular ascites. The sensitivity and specificity increased by combining ascitic fluid ADA and interferon-γ assay.

Molecular and immunological techniques are used for the rapid diagnosis of abdominal TB. It can be tested in any body fluid suspected to have TB, or affected body tissue like lymphnode, thickened omentum or mesentery. Multiplex PCR has sensitivity and specificity of 90% and 100%, respectively in confirmed (AFB/culture/histopathology) cases of gastrointestinal TB and positive results in 72.41% of the suspected gastrointestinal TB case.

Ultrasound: Ultrasound is an initial investigation to pickup lymphadenopathy, tubercular ascites, peritoneal thickening, omental thickening and bowel wall thickening in some cases.

Barium studies used to be gold standard in diagnosing strictures, fistulae, erosions, etc. But now Contrast enhanced CT and CT enterography provide more information not only of intestine but also about surrounding organs.