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Background and Purpose. The head thrust test (HTT) is used to assess the vestibulo-ocular reflex. Sensitivity and specificity for diagnosing unilateral vestibular hypofunction (UVH) in patients following vestibular ablation is excellent (100%), although sensitivity is lower (35%-39%) for patients with nonsurgically induced UVH. The variability of the test results may be from moving the subject's head outside the plane of the lateral semicircular canals as well as using a head thrust of predictable timing and direction. The purpose of this study was to examine sensitivity and specificity of the horizontal HTT in identifying patients with UVH and bilateral vestibular hypofunction (BVH) when the head was flexed 30 degrees in attempt to induce acceleration primarily in the lateral semicircular canal and the head was moved unpredictably. Subjects. The medical records of 176 people with and without vestibular dysfunction (n=79 with UVH, n=32 with BVH, and n=65 with nonvestibular dizziness) were studied. Methods. Data were retrospectively tabulated from a de-identified database (ie, with health information stripped of all identifiers). Results. Sensitivity of the HTT for identifying vestibular hypofunction was 71% for UVH and 84% for BVH. Specificity was 82%. Discussion and Conclusion. Ensuring the head is pitched 30 degrees down and thrust with an unpredictable timing and direction appears to improve sensitivity of the HTT. [ABSTRACT FROM AUTHOR]