Diagnostic value of cold agglutinin test in tuberculosis

Tuberculosis (TB) is a common disease in our society for which acute diagnosis is rather a time-consuming process. Early diagnosis is of utmost importance. Cold agglutinin could serve as a diagnostic modality in patients with TB, thus, the present study was conducted to determine the efficacy of this test in patients with TB and their control group hospitalized in Shaheed Beheshti hospital in Kshan. The study population included 36 cases of TB and 65 non-TB patients. Blood sample (1ml) was obtained and cold agglutinin test was achieved on bed side. Positive agglutinin test was defined as clumping of RBCs in test tube walls and graded as +1 to +4. Absence of RBC agglutinin was considered as negative test result. Finally, sensitivity, specificity, positive and negative predictive values (PPV, NPV) of cold agglutinin was determined in accordance to the definite diagnosis of TB. The TB group included 18 males and 18 females with the mean age of 50.8 years (13-86 years), of whom, 69.5% had pulmonary TB and 30.5% had extra pulmonary TB. If strongly positive cold agglutinin test results are considered, it may have sensitivity of 44.4%, specificity of 98.5%, PPV of 94.1%, NPV of 76.2% and total accuracy of 79.2%. However, if relatively positive results (grade <+3) are considered the sensitivity and specificity may change, improving sensitivity up to 89%. Cold agglutinin test has an acceptable PPV for TB diagnosis. Thus, it could be used as a screening test or as a diagnostic modality in early stage of the disease or even to evaluate the success of treatment.