| 0 Incomplete | Prior CT being located; lungs not evaluable; findings suggesting infection or inflammation | Compare with prior; 1–3 month LDCT for suspected infection |
| 1 Negative | No nodules, or benign calcification / fat | 12-month screening LDCT |
| 2 Benign | Solid < 6 mm at baseline or new < 4 mm; part-solid < 6 mm at baseline; GGN < 30 mm (any status) or ≥ 30 mm stable / slowly growing; juxtapleural < 10 mm, solid, smooth, oval / lentiform / triangular; subsegmental airway nodule; category 3 stable at 6 months; 4B proven benign | 12-month screening LDCT |
| 3 Probably benign | Solid 6 to < 8 mm at baseline or new 4 to < 6 mm; part-solid ≥ 6 mm with solid component < 6 mm at baseline, or new < 6 mm total; GGN ≥ 30 mm at baseline or new; thick-walled cyst with growing cystic component; 4A stable at 3 months (not airway) | 6-month LDCT |
| 4A Suspicious | Solid 8 to < 15 mm at baseline, growing < 8 mm, or new 6 to < 8 mm; part-solid with solid component 6 to < 8 mm at baseline, or new / growing solid component < 4 mm; segmental or more proximal airway nodule at baseline; thick-walled or multilocular cyst at baseline, or a cyst that becomes multilocular | 3-month LDCT; PET/CT may be considered if a solid nodule or component ≥ 8 mm |
| 4B Very suspicious | Solid ≥ 15 mm at baseline, or new / growing ≥ 8 mm; part-solid with solid component ≥ 8 mm at baseline, or new / growing solid component ≥ 4 mm; airway nodule persisting at 3 months; thick-walled cyst with growing wall or nodularity, growing multilocular cyst, or increased loculation / new opacity; slow-growing solid or part-solid nodule | Diagnostic chest CT ± contrast, PET/CT if ≥ 8 mm solid, tissue sampling and/or referral |
| 4X | Category 3 or 4 nodule with additional features that increase suspicion (spiculation, lymphadenopathy, metastatic disease, GGN doubling in a year) | As 4B |
| S | Modifier for a clinically significant finding unrelated to lung cancer | Per ACR incidental findings recommendations |