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©2013 UpToDate ® Print Email Histologic grades of asbestosis Grade Change Gradeof severity 0 No fibrosis associated with bronchioles 1 or I Early fibrosis involving walls of at least onerespiratory bronchiole, with or without extension into septa ofadjacent alveoli; fibrosis confined to alveolated walls of respiratorybronchioles and ducts and not present in more distant alveoli.Alveolitis and inflammation similar to that caused by cigarette smoking 2 or II More severe fibrosis involving acinus: alveolar ductsand/or two or more layers of adjacent alveoli. Normal lung remains in azone between adjacent bronchioles 3 or III Fibrosis advanced and coalescent, involves entireacinus; all lung between at least two adjacent bronchioles is affected.Some alveoli are completely obliterated 4 or IV Honeycomb remodeling and large (up to 1 cm) dilatedspaces grossly visible in parenchyma Gradeof extent A or 1 Only occasional bronchioles are involved. Most appearnormal B or 2 " Morethan occasional" but less than half of bronchioles are involved C or 3 More than half of bronchioles are involved Developed in 1980 by a committee of the College of American Pathologists. Am J Respir Crit Care Med vol 170 pp 692, 2004; www.atsjournals.org.