The Jo-1 Antibody test is used to detect autoimmune antibodies against the enzyme histidyl-tRNA synthetase in the blood. This antibody is specifically associated with Antisynthetase Syndrome, a rare autoimmune disorder with manifestations such as myositis (muscle inflammation), interstitial lung disease (ILD), arthritis, and skin symptoms like mechanic’s hands. The presence of Jo-1 Antibody (the most common antibody in the antisynthetase group) aids in the differential diagnosis between types of myositis (such as polymyositis or dermatomyositis) and other rheumatological diseases. A positive test indicates a potentially more severe disease prognosis, particularly pulmonary involvement, and may also be useful for monitoring treatment response or disease progression. However, results must be interpreted alongside clinical symptoms, imaging (such as lung CT scans), and other tests (such as muscle biopsy), as false positives or false negatives can occur. This test is particularly useful in patients with muscle weakness, unexplained shortness of breath, or multiple autoimmune manifestations.