What VQ scan looks for
Informed by recognized medical guidance
Overview
A VQ scan is a medical imaging test that looks for blood clots in your lungs. It is short for ventilation-perfusion scan. It shows how well air and blood flow through your lungs.
Key facts
- The VQ scan helps diagnose a condition called pulmonary embolism, which is a blood clot in the lung.
- It uses a small amount of radioactive material to create pictures of your lungs.
- It is a safe test and does not cause much radiation exposure.
The VQ scan is a common test when a doctor suspects a blood clot in the lung and a CT scan is not suitable (for example, if you have kidney problems or are allergic to contrast dye).
It is used for people who have symptoms that suggest a blood clot in the lung, such as sudden shortness of breath or chest pain.
Symptoms
- Sudden, severe shortness of breath that does not go away
- Chest pain that is crushing or squeezing, especially with sweating or nausea
- Coughing up a lot of blood
- Fainting or feeling like you might pass out
- ⚠Any new shortness of breath or chest pain that worries you, even if not severe
Common symptoms
- Sudden shortness of breath
- Sharp chest pain that gets worse when you breathe deeply or cough
- Coughing up blood
- Fast or irregular heartbeat
- Feeling lightheaded or dizzy
Symptoms in children
- Children with a blood clot in the lung may have similar symptoms: sudden trouble breathing, chest pain, or fainting.
Symptoms in older adults
- Older adults may have less obvious symptoms, such as just feeling very tired or confused, or having a faster breathing rate.
Causes
Main causes
- A blood clot that forms in a deep vein (usually in the leg) and travels to the lung
Risk factors
- Being immobile for a long time, such as after surgery or on a long flight
- Having had a blood clot before
- Cancer or cancer treatment
- Pregnancy
- Being overweight
- Smoking
- Taking hormone medicines like birth control pills or hormone replacement therapy
When to see a doctor
See a doctor urgently if:
- Any sudden shortness of breath or chest pain should be checked urgently.
Book a routine appointment if:
- If you have had a blood clot before and have new symptoms, see your doctor soon.
Diagnosis
If your doctor suspects a blood clot in your lung, they may order a VQ scan if a CT scan is not right for you.
Tests that may be done
- Ventilation-perfusion (VQ) scan
- Blood test called D-dimer
- CT pulmonary angiography (CTPA) – a different type of CT scan
What to expect at your appointment
During the VQ scan, you will breathe in a gas (a very small amount of radioactive material) and then get an injection of a different radioactive substance. A special camera takes pictures of your lungs. The test takes about 30-45 minutes. It is painless.
Treatment
If a blood clot is found, treatment focuses on stopping the clot from getting bigger and preventing new clots from forming.
Self-care at home
- Stay as active as you can after treatment, but follow your doctor's advice about activity levels.
- Keep your legs elevated when resting to help reduce swelling.
- Wear compression stockings if your doctor recommends them.
Medical treatments
Doctors typically prescribe blood-thinning medicines (anticoagulants) to prevent clots from growing and new clots from forming. This treatment is usually taken for several months or longer, depending on your situation.
When is surgery considered?
In rare cases, if blood thinners do not work or you cannot take them, a filter may be placed in a large vein to catch clots, or surgery may be needed to remove a large clot.
Living with this condition
If you have had a blood clot, you will need to take blood-thinning medicine and have regular check-ups. You may need to avoid activities that cause injury and bleeding, such as contact sports.
Lifestyle tips
- Take your medicine exactly as prescribed.
- Get up and move around often, especially after surgery or long periods of sitting.
- Stay at a healthy weight.
Diet and exercise
Eat a balanced diet with plenty of fruits and vegetables. Exercise most days, but check with your doctor before starting a new activity if you are on blood thinners.
Mental health and emotional wellbeing
Having a blood clot can be frightening. It is normal to feel worried or anxious. Talk to your doctor or a counsellor if you need support.
Prevention
Many blood clots can be prevented by staying active, not smoking, and managing health conditions like obesity.
Vaccines
No vaccines prevent blood clots.
Screening programmes
Screening is not routine, but if you have risk factors, your doctor may discuss prevention strategies such as blood-thinning medicine during hospital stays.
Complications
If left untreated
- The clot can grow and block more blood flow in your lung, making breathing harder.
- The clot can cause damage to your lung tissue.
- In severe cases, a large clot can be fatal.
Long-term outlook
With prompt treatment, most people recover fully from a pulmonary embolism. Taking blood thinners as directed greatly reduces the risk of another clot. Your outlook is good if you follow your treatment plan and have regular follow-ups.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 19, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.