Overview
Adenosine deaminase is an enzyme involved in purine metabolism that catalyzes the conversion of adenosine to inosine and deoxyadenosine to deoxyinosine. It is produced by cells throughout the body and plays an essential role in lymphocyte proliferation and differentiation, particularly T lymphocytes. ADA activity reflects cellular immune activation and is markedly increased in conditions associated with stimulation of cell-mediated immunity, especially tuberculosis. Because of this, ADA estimation is widely used as a supportive diagnostic marker in body fluids.
Symptoms
Altered ADA levels do not cause symptoms directly, but they are associated with underlying diseases. Patients with tuberculosis may present with prolonged fever, weight loss, night sweats, cough, breathlessness, or chest pain, depending on the site involved. Tuberculous meningitis may present with headache, vomiting, altered sensorium, or neck stiffness. In immunodeficiency states such as ADA deficiency, patients—often infants—may present with recurrent severe infections, failure to thrive, and poor immune responses.
Causes
Increased ADA levels are mainly due to activation of cellular immunity. Elevated serum ADA is seen in pulmonary tuberculosis, while high ADA levels in pleural, ascitic, pericardial, synovial fluids, or cerebrospinal fluid are strongly suggestive of tuberculosis at those sites. ADA is also increased in other conditions such as acute and chronic liver diseases, leukemias, and inflammatory or infectious disorders.
Decreased ADA activity occurs in adenosine deaminase deficiency, an autosomal recessive disorder of purine metabolism that leads to severe combined immunodeficiency due to impaired T-cell and B-cell function.
Risk Factors
Risk factors for elevated ADA include exposure to tuberculosis, close contact with infected individuals, immunosuppression, and chronic inflammatory conditions. Populations in TB-endemic regions are at higher risk of showing raised ADA levels in body fluids. Genetic mutations affecting the ADA gene are the main risk factor for ADA deficiency, leading to severe immunodeficiency early in life. A recent blood transfusion can mask ADA deficiency by diluting deficient cells.
Prevention
Early detection and treatment of tuberculosis reduces prolonged immune activation and disease complications. Screening of high-risk individuals and close contacts helps in early diagnosis. In ADA deficiency, early identification allows timely management with enzyme replacement therapy or gene therapy, improving survival and immune function. Proper sample collection, storage, and interpretation of ADA levels in correlation with clinical findings and other investigations are essential for accurate diagnosis and effective patient management.
