Using objective measurements to guide asthma therapy is not a new concept, and it appears to show superior results compared with traditional measures alone (eg, symptoms and lung function).9,11 Although accurate invasive airway measurements are possible, bronchoscopy is expensive, associated with adverse events, and unavailable in routine clinical settings. Thus, research has focused on noninvasive measures of airway inflammation. Although experience with induced sputum has shown valuable results,12-14 there remain significant barriers to its use clinically, including its limited availability in most centers, the timing requirements for urgent samples, and the inability of children (and many adults) to expectorate sufficient and valid samples. Exhaled nitric oxide has shown correlation with asthma inflammation and outcomes experimentally15-17 but it appears to lack the sensitivity and specificity of induced sputum in improving patient outcomes.18 Although other tests for asthma using blood or urine exist (eg, urine leukotrienes, eosinophil cationic protein, C-reactive protein), to date they have not been integrated into clinical practice.19-24 Overall, a simple, noninvasive test for patients with airway inflammation is not widely available, and, in most clinical settings, clinicians simply rely on patient history and individualized therapeutic trials. This strategy can be ineffective, inefficient, and potentially harmful to patients. This article reviews a future diagnostic solution using metabolomics-based biomarkers.