air-trapping [62, 63, 98] . Laboratory tests focus mainly on the search for serum-precipitating IgG antibodies against the offending antigen [95] . However, the presence of these antibodies is considered to be of questionable clinical relevance for diagnosis, as it is observed in up to 50% of serum samples of exposed but asymptomatic individuals. BAL cell profile study typically shows an increase in total cell count with a remarkable elevation in the percentage of lymphocytes often over 50% with a decreased CD4/CD8 ratio [95, 97] . However, in contrast to studies in adults, the CD4/CD8 ratio could be within the normal range for children [76] . Histopathologic evaluation of lung tissue is usually not necessary for the diagnosis of HP.