This test is a key tool for investigating chronic lung conditions. It specifically measures the "memory" (IgG) antibodies your immune system produces in response to Aspergillus, a common mold. A positive test indicates a significant, long-term exposure or a chronic fungal process in the body, such as allergic bronchopulmonary aspergillosis (ABPA). This is essential for patients with asthma or cystic fibrosis who have worsening symptoms. This simple blood test provides the specific, diagnostic clue your doctor needs to find the root cause of your respiratory issues.