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Is serological test sufficient to diagnose tuberculosis?

Q: My 35 years old wife has been suffering from tuberculosis (TB) and serum test result showed IgG - 318 EU/ml, IgM - 3.5. Is the test sufficient to diagnose tuberculosis? The doctor diagnosed the TB in tubes of uterus. Now she has already started taking Monto - 4, Dezole – D and Becap - CZ daily. Please note that five years back my wife suffered from TB in spine and took complete treatment for the same. She is unable to conceive. Please advise.

A:The commercially available serological (blood) tests for the diagnosis of tuberculosis vary widely in performance. The sensitivity of these tests is higher in pulmonary tuberculosis cases (especially if they are smear positive) and range between 63-85% for the IgG tests. The term sensitivity of a test generally means ability of the test to detect all true positives (in this case all patients current or past TB). The specificity of these tests (i.e. the ability to distinguish those individuals without TB from those with TB) is inconsistent and varies between 63-85%. This means that these tests may not only under diagnose TB, but may also incorrectly conclude that some patients are TB positive when they may have some thing else. The data is not comprehensive enough for extra-pulmonary disease, however some studies have reported sensitivity, specificity, positive and negative predictive values like 76, 92, 80, and 90% for extrapulmonary-TB patients. The predictive value of a test reflects the proportion of patients with a positive (or negative test) who are correctly diagnosed.

Serological tests are not sufficient to diagnose tuberculosis. They may help provide some clues and additional information, but because of the inherent limitations of these tests they cannot be (and are often not the only criterion) to make a diagnosis of tuberculosis. When a doctor makes a diagnosis of tuberculosis he/she takes into account a number of factors such as history of present illness, past medical history, physical examination findings, results from imaging studies (X-ray etc), laboratory results (microscopy, culture, and in some cases serology) to make a diagnosis. In cases of extra-pulmonary tuberculosis the diagnosis is more difficult because it is not easy to obtain representative samples for microscopy or microbiologic culture. In many such cases the diagnosis is provisional and treatment considerations may have to take into account diseases, which are common in such clinical setting, local incidence and prevalence of tuberculosis. Response to treatment is often an indication whether treatment is proceeding in the right direction and whether initial diagnosis is correct. It must be remembered that like pulmonary tuberculosis extra-pulmonary tuberculosis (involving organs other than lungs) are treatable and curable conditions. The outcome often depends on extent of the diseases at the time of diagnosis, adherence to treatment, susceptibility of the bacteria to anti-tuberculosis treatment.


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