Lung-RADS

Lung-RADS sorts each screening low-dose CT into a numbered category from 0 to 4, with the 4s subdivided (4A, 4B, and 4X), and adds an optional 'S' modifier for significant incidental findings unrelated to lung cancer. The category reflects the most concerning finding on the exam and is driven mainly by nodule type (solid, part-solid, or ground-glass), size, and whether it is new or growing. Each category carries a recommended management path. Take the exact size thresholds, growth definitions, and follow-up intervals from the official ACR source rather than inferring them.

• 0 — IncompleteCan't be fully assessed yet (prior comparison needed, part of the lung not evaluable, or possible infection/inflammation needing a short-interval recheck).
• 1 — NegativeNo nodules, or only definitively benign findings.
• 2 — Benign appearance/behaviorFindings present but with a benign look or stable benign behavior.
• 3 — Probably benignLow likelihood of cancer; shorter-interval follow-up rather than waiting a full year.
• 4A — SuspiciousEnough concern to warrant additional diagnostic evaluation.
• 4B — Very suspiciousHigher concern, prompting more aggressive workup.
• 4XA category 3 or 4 finding with extra features (e.g. spiculation, suspicious nodes) that raise suspicion further.
• S (modifier)A significant or potentially significant incidental finding unrelated to lung cancer, appended to any category.

These are our plain-language summaries. For the exact criteria, thresholds, and management rules, see the official source.

The cleanest contrast is Lung-RADS versus the Fleischner Society guidelines: Lung-RADS governs organized screening of asymptomatic high-risk people on repeated annual low-dose CT, while Fleischner addresses nodules found incidentally on a CT done for some other reason. They are not interchangeable — Fleischner explicitly defers to Lung-RADS for screen-detected nodules — and applying the wrong one can change follow-up timing and biopsy thresholds for the same nodule. Lung-RADS is also distinct from non-U.S. screening frameworks such as the British Thoracic Society guidance. (Note: U.S. Medicare coverage requires a standardized classification/reporting system without naming Lung-RADS exclusively, but Lung-RADS is the de facto standard.)

The case for low-dose CT screening that Lung-RADS operationalizes rests on two landmark randomized trials: the U.S. National Lung Screening Trial showed roughly a 20% relative reduction in lung-cancer mortality versus chest radiography, and Europe's NELSON trial confirmed a comparable benefit with a volume-based approach and low workup rates. Retrospective application of Lung-RADS to NLST data sharply lowered false-positive rates versus the trial's original criteria, at the cost of modestly lower sensitivity. Reliability is generally good for solid nodules but degrades for subsolid ones, where a small solid component reduces agreement. A practical caveat is that Medicare eligibility is slightly narrower than the 2021 USPSTF recommendation (age 50–80, at least 20 pack-years).

Who is Lung-RADS for?

People undergoing organized lung-cancer screening with low-dose CT — generally older adults with a substantial smoking history. It is not meant for nodules found incidentally on other scans.

Does a Lung-RADS category 4 mean I have lung cancer?

No. It signals enough suspicion to justify further evaluation; most flagged findings still turn out not to be cancer after workup.

What is the 'S' on my report?

The S modifier flags a significant incidental finding unrelated to lung cancer that may deserve attention on its own.

How is Lung-RADS different from the Fleischner guidelines?

Lung-RADS is for repeated screening of high-risk people; Fleischner is for nodules found incidentally during other imaging. They use different logic and are not interchangeable.

Which version is current?

Lung-RADS v2022, released in late 2022 and still current in 2026.

LDCT (low-dose CT)

A reduced-radiation chest CT used as the screening test for lung cancer in high-risk adults.

Solid nodule

A nodule of uniform soft-tissue density that hides the lung behind it.

Part-solid nodule

A nodule with both solid and hazy (ground-glass) components; the solid part mainly drives risk.

Ground-glass / nonsolid nodule

A hazy nodule through which lung vessels remain visible; usually lower immediate risk.

NLST

The National Lung Screening Trial, which showed low-dose CT screening reduces lung-cancer deaths.

USPSTF

The U.S. Preventive Services Task Force, which sets lung-screening eligibility recommendations.

S modifier

An added flag for a significant incidental finding unrelated to lung cancer.

• officialACR Lung-RADS official page
• referenceACR Lung-RADS v2022 criteria paper (PubMed)
• patientRadiologyInfo.org — reading your lung-screening report (patient)
• calculatorLung-RADS v2022 calculator (third-party, link-only)