This disclosure provides a robust, sensitive, and specific assay for the detection and measurement of periostin levels in samples obtained from human patients having, or suspected of having an IL-13-mediated disease or disorder. The disclosure further provides novel antiperiostin monoclonal antibodies that recognize at least isoforms 1, 2, 3, 4, 7, and 8 of human periostin, and assay kits comprising one or more of these antibodies.