Histopathological grading scale of chemically induced colitits
| Grade of colitits | Microscopic findings |
| 0 | Histological findings identical to normal rats |
| 1 | Mild mucosal and/or submucosal inflammatory infiltrate (admixture of neutrophils) and oedema. Punctate mucosal erosions often associated with capillary proliferation. Muscularis mucosae intact. |
| 2 | Grade 1 changes involving 50% of the specimen. |
| 3 | Prominent inflammatory infiltrate and oedema (neutrophils usually predominating) frequently with deeper areas of ulceration extending through the muscularis mucosae into the submucosa. Rare inflammatory cells invading the muscularis propriae but without muscle necrosis. |
| 4 | Grade 3 changes involving 50% of the specimen. |
| 5 | Extensive ulceration with coagulative necrosis bordered inferiorly by numerous neutrophils and lesser numbers of mononuclear cells. Necrosis extends deeply into the muscularis propria. |
| 6 | Grade 5 changes involving 50% of the specimen. |