At the present time, there is no diagnostic test that is pathognomonic for HP, and only significant predictors of HP are identified. The most significant diagnostic tool is a detailed environmental exposure history. Other diagnostic features include: positive precipitating antibodies to the offending antigen; recurrent episodes of symptoms; symptoms occurring 4-8 h after exposure; occurrence of diffuse parenchymal lung disease by lung function and HRCT; BAL abnormalities with lymphocytic alveolitis and increased CD8+ T cells.