Lung Cancer Screening with Low-Dose CT: What to Expect and What the Results Mean

Research-informed explainer — last updated April 12, 2026

Annual low-dose CT (LDCT) scanning is the only imaging test proven to reduce lung cancer mortality — but the scan itself is just the beginning of a process that requires informed interpretation and, in most cases, follow-up rather than immediate intervention. Knowing who qualifies, what happens during the scan, and what the results mean reduces anxiety and helps patients act on findings promptly.

This article draws on research from David Midthun, MD, Professor of Medicine at Mayo Clinic, who published the first large prospective LDCT screening trials and contributed to NCCN lung cancer screening guidelines; Fabien Maldonado, MD, Professor of Medicine and Thoracic Surgery and Director of Interventional Pulmonology at Vanderbilt University Medical Center; Peter Mazzone, MD, at Cleveland Clinic, who has studied biomarkers in lung cancer screening; and Raed Dweik, MD, a Staff physician at Cleveland Clinic with expertise in exhaled biomarker detection.

Who Qualifies for Annual LDCT Screening

Current U.S. Preventive Services Task Force and CMS criteria recommend annual LDCT for adults aged 50 to 80 who have a 20 pack-year smoking history and currently smoke or quit within the past 15 years. These eligibility criteria were informed in part by the National Lung Screening Trial (NLST), which enrolled over 53,000 current or former smokers and found a 20% reduction in lung cancer mortality with annual LDCT compared to chest X-ray.

The criteria exist because LDCT screening carries real costs: radiation exposure, false positives requiring additional testing, and — in rare cases — complications from invasive follow-up procedures. Screening works when the population has sufficient baseline risk to justify these trade-offs. Applying it to everyone who ever smoked a cigarette would generate far more harm than benefit.

What Happens During the Scan

LDCT is a brief, non-invasive procedure. You lie flat on a table that slides through a ring-shaped scanner. The scan itself takes under 10 minutes and requires a single breath-hold of about 6 seconds. No IV contrast is used. Radiation dose is approximately 1.5 mSv — roughly the equivalent of 6 months of natural background radiation, and substantially less than a standard diagnostic CT of the chest.

The images are reviewed by a radiologist trained in thoracic imaging. Findings are reported using a standardized classification system called Lung-RADS, developed by the American College of Radiology, which assigns categories from 1 (nothing abnormal) to 4 (suspicious finding warranting prompt workup).

Understanding Pulmonary Nodules

The most common finding on LDCT is a pulmonary nodule — a small, rounded density in the lung. Dr. Midthun's foundational Mayo Clinic work, published in Radiology and cited more than 650 times, established that the overwhelming majority of nodules found on screening CT are benign. In the 5-year Mayo Clinic prospective experience, approximately 51% of participants had at least one nodule detected, but less than 2% of all nodules represented lung cancer.

The key variables that determine follow-up are nodule size, morphology (solid versus subsolid), and growth rate. Lung-RADS 1 and 2 nodules (small, stable, solid) require only routine annual screening. Lung-RADS 3 nodules (6-8mm solid, or smaller subsolid) trigger a 6-month follow-up CT. Lung-RADS 4A and 4B findings prompt PET/CT imaging, bronchoscopy, or surgical consultation depending on clinical context.

Dr. Midthun's CHEST Journal paper (cited more than 1,400 times) synthesized the evidence on how to evaluate individuals with pulmonary nodules found incidentally or on screening CT. Size thresholds for biopsy have evolved: nodules under 6mm solid are almost never biopsied on first detection. The issue is not whether a nodule exists, but whether it is growing.

What "False Positive" Means — and Why It Matters

A false positive in LDCT screening means a finding that looked suspicious but turned out not to be cancer — typically because no growth was observed on follow-up imaging. In the NLST, approximately 39% of patients who underwent LDCT had at least one positive screen over 3 years; of these, only 3.8% were true cancers. The false positive rate is high, but the downstream procedures required to resolve most false positives are low-risk (a follow-up CT) rather than high-risk (surgery).

This context is important for patients who receive a "positive" result and spiral into anxiety. In the vast majority of cases, a positive screen means "we found something that requires a follow-up scan in 6 months" — not "you have cancer."

Biomarkers: The Next Frontier

Dr. Mazzone's Journal of Thoracic Oncology paper on biomarkers in lung cancer screening (cited 562 times) reviews blood-based protein biomarkers, circulating tumor DNA, and exhaled volatile organic compounds as potential adjuncts to LDCT. Currently, no biomarker test is approved as a standalone screening tool or as a replacement for CT. However, blood-based tests may eventually help resolve indeterminate nodules by raising or lowering the pre-test probability of malignancy — potentially avoiding some diagnostic procedures.

Dr. Dweik's Cleveland Clinic work on exhaled nitric oxide and breath-based diagnostics provides supporting evidence that airway chemistry reflects underlying lung pathology. Breath sensors capable of detecting lung cancer-associated volatile compounds have shown promise in small studies, but require larger validation trials before clinical adoption.

After an Abnormal Result: What the Process Looks Like

If a Lung-RADS 4 finding is identified, the typical pathway involves:

1. A PET/CT scan to assess metabolic activity of the nodule
2. If PET-positive and technically accessible: bronchoscopic or CT-guided needle biopsy
3. If biopsy confirms malignancy: surgical staging and resection planning

For patients with early-stage lung cancer detected on screening, the five-year survival rate exceeds 80% — compared to less than 20% for patients diagnosed with advanced disease. That survival difference is the reason screening exists.

Questions to ask your doctor

• Do I meet the age and smoking history criteria for annual LDCT screening?
• What does my Lung-RADS score mean, and what is the recommended follow-up interval?
• If a nodule was found, what size threshold would prompt a biopsy recommendation?
• Are there any breath or blood biomarker tests that might help clarify an indeterminate finding?
• What radiation exposure am I accumulating from annual scans, and how does that compare to my cancer risk?

The bottom line

Annual low-dose CT screening reduces lung cancer mortality by 20% in high-risk current and former smokers — but most people who screen positive have benign nodules that require follow-up imaging rather than immediate intervention. Understanding the Lung-RADS classification system, the role of nodule size and growth, and the current limitations of biomarker testing helps patients engage with their results clearly rather than reflexively. If you are between 50 and 80 with a 20 pack-year history, ask your doctor whether annual LDCT is right for you.