When these conditions have been eliminated, the spectrum of investigations that should be performed for the diagnostic approach will be guided by the history and clinical presentation in each individual child. These investigations are discussed below for the various disorders. In addition, an increasing number of blood and BAL biomarkers for evaluation of disease severity and progression is currently investigated. The studied molecules include various cytokines and chemokines, surfactant protein D, Krebs von den Lungen-6 antigen (KL-6), matrix metalloproteinases MMP1 and MMP7 and defensins [89] [90] [91] [92] .