An elderly resident has a persistent cough and prior negative tuberculosis tests. In addition to a chest X-ray, what is the next best test to order?

In this scenario, where an elderly resident presents with a persistent cough and has had prior negative tuberculosis tests, ordering an Interferon gamma release assay (IGRA) is a crucial next step after the chest X-ray. IGRA is a blood test that detects the immune response to specific TB antigens, making it a valuable tool for diagnosing latent tuberculosis infection (LTBI) in individuals who have been exposed to the bacteria but do not exhibit active disease.

The use of IGRA is particularly beneficial in this case because it has higher specificity and sensitivity compared to traditional methods, such as the tuberculin skin test (TST), especially in populations like the elderly, who may not mount a strong immune response. Furthermore, IGRA does not require a follow-up visit for reading, unlike the TST, making it more practical in many clinical settings.

In contrast, while a Complete Blood Count (CBC) may provide insight into the overall health of the patient, it is not specific for diagnosing tuberculosis. Sputum cultures, although useful for identifying active TB by detecting the bacteria, are more appropriate if the suspicion for active TB is high based on clinical findings and imaging results. The tuberculin tine test is also less favorable in this context due to