Lung CT Screening & Incidental Lung Nodules

This page is for people weighing lung cancer screening, and for anyone whose CT scan found a lung nodule. It covers who qualifies, what the scan finds, and how to tell which follow-up rules apply to you.

The USPSTF recommends annual low-dose CT for adults aged 50 to 80 who have at least a 20 pack-year smoking history. The recommendation covers people who either still smoke or quit within the past 15 years. It carries a Grade B. That means the Task Force found moderate net benefit and recommends offering it.

A pack-year is one pack a day for one year. Half a pack a day for 40 years counts the same as two packs a day for 10. Work out your own total before the appointment. Eligibility and insurance coverage both turn on that number.

The recommendation also says when to stop. That is once you have not smoked for 15 years, or once a health problem would prevent you from tolerating curative lung surgery. Screening only helps if a found cancer can be treated.

The National Lung Screening Trial found a 20 percent reduction in lung cancer deaths with annual low-dose CT compared with chest X-ray. The European NELSON trial pointed the same way. After at least 10 years of follow-up, NCI reports a lung cancer mortality rate ratio of 0.76 in screened men compared with usual care.

Overdiagnosis is the harm people most want a number for. NCI does not give one. It says some cancers found by screening do appear to be overdiagnosed. But it says published estimates vary a lot, so the true size is not clear.

Many scans show small spots in the lungs. Most are not cancer, but some need a repeat scan or more tests.

The Lung-RADS system gives each scan a category. Categories 1 and 2 both mean annual screening continues, with the next scan in 12 months. Category 3 is "probably benign" and brings a 6-month repeat scan. Category 4A moves to a 3-month scan, and 4B or 4X to further imaging or tissue sampling.

Lung-RADS also changed what gets called positive at all. NCI says that using Lung-RADS gives somewhat lower false-positive rates than the definition used in the National Lung Screening Trial. A false positive can still mean extra scans or tests, so it helps to know that going in.

Reports can use different systems, and that can be confusing.

If a nodule is found on a lung cancer screening CT, the report uses Lung-RADS categories.

If a nodule is found incidentally, it was seen on a CT ordered for another reason, such as chest pain, an injury, or before surgery. Radiologists often follow different guidelines for those nodules, and the follow-up plan can differ from Lung-RADS. We have not confirmed the details of those guidelines in NCI or CDC sources, so this page does not list them.

If you are trying to make sense of a report, the first question is which system was used. A category number means Lung-RADS. Ask your doctor to explain any other plan, and why it was chosen.

Screening has real benefits, and it also has downsides. Here are the main ones.

Findings outside the lungs. The scan also shows nearby structures, so it can find things that are not in the lungs. Lung-RADS flags significant ones with an S modifier. Some of these findings lead to more tests that end in nothing.

Radiation. The dose per scan is small. NCI reports a mean effective dose of 1.4 mSv for low-dose CT in the National Lung Screening Trial. It estimates that participants received about 8 mSv over three years of screening once follow-up imaging is counted. The dose adds up across years of annual scans. NCI says the benefits outweigh the radiation risk for people at high risk, and the USPSTF limits screening to appropriate candidates.

Procedures. NCI says false positives can lead to unnecessary invasive procedures, and tests after a scan can cause complications.

Screening is a program, not an event. The USPSTF recommends annual scans, and any follow-up scan needs to be booked on time. A common problem is a 6-month or 3-month recommendation that quietly never gets booked.

Before you leave, write down the category, the exact next date, and who is responsible for reminding you. Quitting smoking lowers lung cancer risk, so ask for help at the same visit.

• NCI: Lung Cancer Screening (PDQ) - Patient Version
• NCI: Lung Cancer Screening (PDQ) - Health Professional Version
• USPSTF evidence report, NCBI Bookshelf — Screening for Lung Cancer With Low-Dose Computed Tomography