Starting from symptoms in a patient, physicians will decide to start or withhold TB treatment, or otherwise invest resources in additional tests. In practice, when confronted with diagnostic uncertainty, the clinician will consider potential harm and benefit of offering versus withholding treatment.
To help guide this process, we need to estimate: (1) the probability of TB in a patient with a given background and set of symptoms and test results, and (2) the therapeutic threshold, this is the probability of TB that needs to be exceeded to start treatment.
As part of the TB TRIAGE+ project, we aim to determine (1) the diagnostic accuracy of all diagnostic information, be it symptoms, tests or risk factors and (2) the therapeutic threshold of TB in the setting of rural Lesotho and South Africa. Obviously, the HIV status of a patient also influences the probability of TB and the presentation of TB will vary depending on the level of immunosuppression. We will therefore also assess the diagnostic accuracy of a new low-cost point-of-care CD4 test to identify patients with a low CD4 count.
By combining and analyzing the information we collect in this project, we foresee that we can obtain accurate estimates of these concepts. Those can subsequently be used in the development of an evidence-based clinical decision tool for TB.
With such a tool, clinicians will be able to determine if a new patient with given demographics and symptoms reaches the threshold to start treatment. Additionally, if an additional diagnostic test is available, the tool will inform the clinician whether doing such a test has added value. If the probability of TB is in the yellow area (figure below), the test result will influence the decision to treat, while alternatively the decision to treat or withhold treatment can be taken without further testing.