Mycobacterium tuberculosis primarily infects the lungs, but the bacteria may move into the blood stream and seed other organs. Quick diagnosis is critical for infections of vital organs, such as the brain or heart. The gold standard for diagnosis of tuberculosis is the demonstration of Mycobacteria tuberculosis in a human sample. Mycobacteria grow very slowly, and the diagnosis requires a long time, usually 10 days to 4 weeks. Adenosine deaminase assay promises a much faster and cost-efficient diagnostic tool for tuberculosis.
Adenosine Deaminase, ADA
Adenosine consists of a purine molecule, called adenine, and a sugar molecule, called ribose. Adenosine is an essential component of DNA that conserves genetic information. Furthermore, adenosine triphosphate is the molecular form for energy storage obtained from food and then transformed through a series of reactions to a structure that can be used in biochemical reactions of your body. The enzyme ADA irreversibly converts adenosine to inosine. The conversion speed determines the activity of the enzyme and is measured in the assay. Levels of ADA increase in fluids surrounding inflamed tissue, including cancer, pneumonia and tuberculosis.
ADA and Lung Tuberculosis
During inflammation, lungs secrete fluid into the narrow space between the lungs and the chest wall. Physicians obtain the fluid by inserting a needle into this space and use it for laboratory analysis. In patients with tuberculosis, ADA concentrations in pleural fluid rise above the levels of patients with cancer, pneumonia or other lung diseases. Other studies also indicate that ADA assay is relatively sensitive and a specific test for the diagnosis of tuberculosis.
ADA and Meningeal Tuberculosis
Mycobacteria may seed in the parenchyma or brain covers, called meninges. Brain inflammation is a serious medical condition for which time plays critical role. ADA assays are completed within several hours. The assays are sensitive and specific for tuberculous meningitis.
ADA and Tuberculosis of the Heart
Tuberculosis of the heart is another life-threatening situation. ADA levels rise in fluid that surrounds the heart. Determination of ADA levels in the pericardial fluid appears useful in the diagnosis of tuberculous pericarditis.
References
- "Journal of Clinical Microbiology"; Comparison of mycobacteria growth indicator tube with BACTEC 460 for detection and recovery of mycobacteria from clinical specimens; Badak FZ et al.; September 1996
- "Physiological Basis of Medical Practice"; John B West, Md, PhD, DSc; 1990
- "Chest"; Adenosine Deaminase in the Diagnosis of Tuberculous Pleural Effusions. A Report of 218 Patients and Review of the Literature; .Bañales JL et al.; February 1991
- "Respiratory Medicine"; Diagnostic Accuracy of Adenosine Deaminase in Tuberculous Pleurisy: A Meta-Analysis.; Liang QL et al.; May 2008
- "International Journal of Tuberculosis and Lung Diseases."; Diagnostic value of adenosine deaminase in cerebrospinal fluid for tuberculous meningitis: a meta-analysis; Xu HB et al.; November 2010
- "Acta Tropica"; Adenosine Deaminase and Tuberculous Pericarditis - As Systematic Review With Meta-Analysis; Tuon FF et al.; August 2006
