What is the appropriate initial investigation for bilateral non-pulsatile tinnitus without other symptoms?

For a patient presenting with bilateral non-pulsatile tinnitus without any other symptoms, the initial investigation that is most appropriate is an audiogram. An audiogram is a test that assesses a person's hearing ability and can help determine if there is any underlying hearing loss, which is often associated with tinnitus. Tinnitus can arise from a variety of causes, including exposure to loud noise, age-related hearing loss, and ear infections, making the assessment of hearing function crucial in understanding the underlying issue.

An audiogram is a non-invasive and straightforward test that can provide immediate insights into the auditory system’s health. If hearing loss is detected, further investigations or referrals can be made based on the specific findings. This step addresses the most common and relevant causes of tinnitus, making it a logical first approach.

Other investigations like a CT scan of the brain would typically be reserved for cases where there are red flag symptoms indicative of serious underlying conditions, such as unilateral tinnitus, neurologic signs, or significant hearing loss. Similarly, vestibular testing is more appropriate in cases where there are balance issues or vertigo present. Blood tests for infection are generally not relevant unless there are accompanying systemic symptoms that suggest an infectious process. In the absence of such symptoms, these options do not align