Table 1.

Lung histology scoring system

Score	Vascular features	Extravascular and alveolar involvement	Bronchiole features
0	Minimal	Minimal	None
1	Blood leaking into interstitium; mild RBC obstruction	Mild inflammatory exudate; areas of patchy oedema with some disordered structure	Mild infiltration of inflammatory cells
2	Mild RBC and vascular obstruction; areas of mild and moderate haemorrhage	Moderate inflammatory exudate; areas of moderate alveolar thickening (25–50% visualized lung)	Moderate infiltration of inflammatory cells; detachment of lining in some bronchioles
3	Diffuse haemorrhage; moderate RBC and vascular obstruction	Moderate-severe inflammatory exudate; Severe alveolar thickening (> 50% visualized lung); loss of structure with amorphous material	Complete loss of bronchiole structure; detachment of lining; cellular debris and inflammatory cell exudate

RBC red blood cell