Lung Cancer Screening: Low-Dose CT Scan

Test Overview

Screening tests help your doctor look for a problem before you have symptoms. Lung cancer screening is a way to find some lung cancers early, when a cure is more likely and when cancer is more treatable.

If your doctor recommends lung cancer screening, you'll have a low-dose CT scan of your chest once a year. A special scanner called a spiral CT makes circular movements around your body. This doughnut-shaped machine sends low-dose X-rays, or radiation, through your chest to make detailed pictures. A low-dose CT uses much less radiation than a regular-dose CT scan. A doctor looks at the pictures of your lungs for growths, called nodules, that could be cancer.

Why It Is Done

Most people don't need routine lung cancer screening. It's only recommended for people age 55 and older who are, or were, heavy smokers with a smoking history of at least 30 pack years. A pack year is a way doctors measure how much you have smoked.

To figure out your pack years, multiply how many packs a day (assuming 20 cigarettes per pack) you smoke by how many years you have smoked.

For example:

  • If you smoked 1 pack a day for 15 years, that's 1 times 15. So you have a smoking history of 15 pack years (1 x 15 = 15).
  • If you smoked 1½ packs a day for 20 years, that's 1.5 times 20. So you have a smoking history of 30 pack years (1.5 x 20 = 30).
  • If you smoked 2 packs a day for 15 years, that's 2 times 15. So you have a smoking history of 30 pack years (2 x 15 = 30).

Your doctor may recommend that you get screened each year if:

  • You are 55 to 80 years old.
  • And you have a smoking history of at least 30 pack years.
  • And you still smoke, or you quit within the last 15 years.
  • And you are in good health overall. Having a serious health problem might mean that you couldn't, or wouldn't want to, have treatment for lung cancer. The treatment could be too high-risk, and it might not help you live longer.

How To Prepare

Before a low-dose CT scan to screen for lung cancer, tell your doctor if you have a heart condition, such as heart failure.

Talk to your doctor about any concerns you have about your need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form.

How It Is Done

A CT scan is usually done by a radiology technologist. The pictures are usually read by a radiologist, who writes the report. Other doctors also may review a CT scan.

You may need to take off any jewelry, and some clothing, such as a bra. You will be given a gown to use during the test.

During the test, you will lie on a table that is attached to the CT scanner.

The table slides into the round opening of the scanner, and the scanner moves around your body. The table will move while the scanner takes pictures. You may hear a click or buzz as the table and scanner move.

It is very important to lie still during the test.

During the test, you may be alone in the scan room. But the technologist will watch you through a window. You will be able to talk to the technologist through a two-way intercom. The test will take about 30 minutes. For most of this time, you'll be getting ready for the scan. The actual scan only takes a few seconds.

How It Feels

The test will not cause pain.

The table you lie on may feel hard, and the room may be cool.

It may be hard to lie still during the test. Some people feel nervous inside the CT scanner. Tell the technologist or doctor how you feel.


  • Scans aren't perfect tests. They may not show lung cancer that is there. This is called a false-negative result.
  • The scan may show spots on your lungs that aren't cancer. This is called a false-positive result. This leads to more tests to make sure you don't have cancer.
  • Some screenings find lung cancers that wouldn't have needed treatment if they had not been found. This is called overdiagnosis. But because doctors can't tell which cancers will turn out to be harmless, most will be treated. This means that you may get treatment—including surgery, radiation, or chemotherapy—that you don't need.
  • Even though the dose of radiation for this type of CT scan is low, having this test each year increases your radiation exposure. There is a small chance of getting cancer from that extra exposure.
  • The scan can show problems in the chest that need more testing to confirm that they're not harmful. This is called an incidental finding.


Your doctor will likely get back to you with complete results in 1 to 2 days.

Low-dose CT scan to screen for lung cancer


No growths (nodules) were found in your lungs.

Next step: Another low-dose CT scan to screen for lung cancer in 1 year.


A nodule or nodules were found, but because of their small size, you don't need anything else right now.

Next step: Another low-dose CT scan to screen for lung cancer in 3 to 6 months.

A nodule or nodules were found, and at least one of them is large enough for your doctor to talk to you about having more tests now.

Next step: Your doctor may suggest any of these tests:

  • More scans, such as a CT scan or PET scan.
  • Bronchoscopy, which is a procedure that lets your doctor look into your airway.
  • Biopsy, which is the only way to diagnose cancer. In a biopsy, the doctor takes a sample of tissue from inside your lung so it can be looked at under a microscope.

What Affects the Test

You may not be able to have the test, or the results may not be helpful, if:

  • You are not able to lie still during the test.

What To Think About

  • A biopsy is the only way to diagnose lung cancer. A screening scan shows spots, but the only way a doctor can know if a growth is cancerous is to take a small sample and look at it under a microscope for cancer cells.
  • If you smoke, stopping is the best way to lower the chance of getting and dying from lung cancer. Not smoking helps more than lung cancer screening does. Your doctor may recommend medicines to help you quit.


Current as of: December 17, 2020

Author: Healthwise Staff
Medical Review:
Martin J. Gabica MD - Family Medicine
Kathleen Romito MD - Family Medicine
Howard Schaff MD - Diagnostic Radiology

Lung Cancer Screening: Low-Dose CT Scan