Blood tests aren’t typically used to diagnose lung cancer, but they can give your doctor a general sense of your overall health. Once you have a lung cancer diagnosis, your doctor can use blood counts and blood-based genetic tests to help choose the best treatment for your particular case.

Lung cancer is one of the leading causes of cancer deaths in the United States and is often diagnosed too late. Only about 15 percent of lung cancer cases are detected in the earliest stages, before the cancer has spread.

You may be initially diagnosed with lung cancer based on your symptoms. Then certain tests — such as X-rays, scans, and biopsies — can help your doctor confirm their suspicions. The most common symptoms for lung cancer include a bad cough that won’t go away, chest discomfort, shortness of breath, and spitting up blood.

In general, blood tests aren’t used to diagnose lung cancer. They can help your doctor figure out which treatment options might work best for you or how the cancer or cancer treatment is affecting your body.

Once you’re diagnosed with lung cancer, your doctor might perform the following blood tests.

Complete blood count (CBC)

This test checks the amounts of each type of blood cell in your blood. For example, if you have a low number of red blood cells, you have anemia and may experience fatigue or shortness of breath. If you have a low number of white blood cells, you have a higher risk of infections. A low platelet count puts you at risk for internal bleeding.

A CBC has many uses. For example, it can help your doctor see if you’re healthy enough for surgery, or how your body is responding to a chemotherapy treatment.

Blood chemistry tests

These tests measure levels of certain chemicals in the blood to check for abnormalities in your organs, such as your liver. If the cancer has spread to the liver, for example, you may have higher-than-normal levels of a chemical known as lactate dehydrogenase (LDH).

Blood-based gene mutation tests (companion diagnostic tests)

Certain drugs approved for treating lung cancer are only effective in people with specific types of tumors. These genetic tests are often called “companion diagnostics” because they provide information that’s essential for the safe and effective use of a corresponding drug. While most of these tests are done on a tissue biopsy, some can be done using a blood-based test.

While there aren’t any blood tests currently available to diagnose lung cancer in its earliest stages, there are several in the research stages. These tests rely on detecting DNA changes or chemicals in the blood, called biomarkers, that are only present in people with lung cancer.

When you schedule your blood test, pay attention to any specific instructions your doctor might have given you. For example, your doctor may require that you not eat or drink anything for a certain amount of time before the test.

On the day of your blood test, try to wear a short-sleeved shirt or a shirt with sleeves that are easy to roll up. Blood will likely be taken from your arm on the inside of your elbow, and the phlebotomist (person trained to draw blood) will need to be able to access that area easily.

The test will only take a minute or two. In general, the procedure is as follows:

  1. The phlebotomist will clean your skin with an antiseptic wipe.
  2. They’ll place an elastic band (tourniquet) around the upper part of your arm.
  3. They’ll insert a needle into the vein.
  4. The phlebotomist will collect blood into one or more vials.
  5. They’ll remove the elastic band.
  6. You’ll get a bandage over the area where the needle was inserted.
  7. Your blood sample will be labeled and sent to a laboratory for analysis.

Blood tests can be mildly uncomfortable. You’ll probably feel a sharp pinch when the needle punctures your vein. You also might have a bruise on your inner elbow for a few days.

Your results will be available a few hours to a few days after your blood test. Your doctor may go over abnormal results of a CBC test or a blood chemistry test with you in person.

Your doctor likely won’t make a decision based on the results of just one blood test. They may need to order another blood test to confirm results or other tests to help further evaluate your condition. Try not to leave your doctor’s office confused or uncertain about what your results mean. This is your time to ask questions about what your results mean for your cancer treatment and outlook.

Blood tests for lung cancer aren’t typically done for diagnostic purposes. Your doctor will have already confirmed with other tests and scans that there is a tumor in your lungs.

People with a confirmed diagnosis of lung cancer will likely need to have blood tests at some point. Your doctor will determine which specific tests are relevant and necessary.

There are many different ways to detect lung cancer. Even if you don’t have any signs or symptoms of the disease, a tumor might be discovered in a chest X-ray during a routine checkup or prior to surgery for something else.

However, regular chest X-rays aren’t considered reliable enough to find lung tumors in their earliest stages. The American Society of Clinical Oncology now recommends yearly screenings in people who are at high risk of lung cancer using a procedure called low-dose computed tomography (LDCT). You are considered high-risk if you meet all of the following criteria:

  • between the ages of 55 and 74
  • a smoker or former smoker with a 30-pack year history (for example, smoked a pack a day for 30 years, or two packs a day for 15 years)
  • either continue to smoke or have quit within the last 15 years

If lung cancer is found following a scan, a doctor will likely perform a biopsy. In a biopsy, a small piece of tissue from the lung is removed and examined under a microscope to look for cancer cells. If you have a cough that produces sputum, your doctor may also look at the sputum under the microscope to look for cancer cells.

Additional lung cancer tests include:

  • physical examination to check your vital signs and listen to your lungs
  • MRI scan
  • positron emission tomography (PET) scan
  • thoracentesis
  • bronchoscopy
  • ultrasound
  • mediastinoscopy / mediastinotomy
  • lung function tests
  • thoracoscopy
  • tissue-based gene mutation tests

Most of these tests are used to find out if the cancer has spread beyond the lungs. They can help your doctor with a process known as lung cancer staging. Not every test is appropriate for every person.

After you have blood tests for lung cancer, schedule some time to sit down with your doctor and go over your results. The results from the blood tests and other tests should give your doctor a clearer picture of your overall health and a better idea of which treatment options may be most effective for the specific type of lung cancer you have. As you go through your test results, make sure you cover the following:

  • What type of lung cancer do I have?
  • What is the stage of my lung cancer?
  • Has it spread to other parts of my body?
  • Will I need more tests?
  • Do I have any of the gene mutations eligible for a specific treatment option?
  • What are my treatment options?
  • Should I have surgery?
  • What are the short- and long-term side effects of each treatment?
  • Is there one treatment that you think is best?
  • Are there ways to relieve my symptoms?
  • Should I see a specialist? What will that cost?
  • What does my insurance cover?