VQ scan patient guide
Informed by recognized medical guidance
Overview
A VQ scan (ventilation-perfusion scan) is a safe imaging test that checks how well air and blood flow through your lungs. It uses a small amount of a radioactive tracer to create pictures. Doctors often use it to look for blood clots in the lungs (pulmonary embolism).
Key facts
- It is a nuclear medicine scan – you inhale or receive an injection of a tiny amount of radioactive material.
- The scan has two parts: ventilation (air flow) and perfusion (blood flow).
- It exposes you to a very low level of radiation, similar to a few chest X-rays.
- Results usually come back within a day or two.
VQ scans are a common test when a doctor suspects a pulmonary embolism and the person cannot have a CT scan (for example, due to kidney problems or a contrast allergy).
The test is used for people of any age who have symptoms like sudden shortness of breath, chest pain, or coughing up blood. It may also be used to check lung function before surgery.
Symptoms
- Sudden severe difficulty breathing
- Chest pain that feels crushing or squeezing
- Coughing up a large amount of bright red blood
- Fainting or loss of consciousness
- ⚠Unexplained shortness of breath that does not go away with rest
- ⚠Chest pain that comes and goes
- ⚠Swelling or pain in one leg (could be a deep vein thrombosis)
Common symptoms
- Sudden shortness of breath
- Sharp chest pain that gets worse when you breathe deeply or cough
- Coughing up blood
- Rapid heart rate
Symptoms in children
- Breathing faster than usual
- Pale or bluish skin
- Complaining of chest pain
- Unexplained fainting
Symptoms in older adults
- Sudden confusion or dizziness
- Shortness of breath with little activity
- Chest tightness or discomfort
- Feeling very weak or faint
Causes
Main causes
- A VQ scan does not diagnose causes – it detects blood flow problems. The most common reason for an abnormal result is a pulmonary embolism (a blood clot that traveled to the lungs).
- Other causes of abnormal blood flow include lung diseases like COPD or pneumonia, or a collapsed lung.
Risk factors
- Recent surgery or injury (especially hip or leg surgery)
- Prolonged immobility (long flights, bed rest)
- Cancer or cancer treatment
- Pregnancy or recent childbirth
- Obesity
- Smoking
- Previous blood clots or family history of clots
When to see a doctor
See a doctor urgently if:
- If you have sudden shortness of breath or chest pain, seek emergency care immediately.
Book a routine appointment if:
- If you have persistent leg swelling or pain, or unexplained breathlessness, make an appointment with your GP.
Diagnosis
A VQ scan is part of the diagnostic process for pulmonary embolism. Your doctor will first assess your symptoms, risk factors, and may do a blood test (D-dimer). If needed, they will refer you for a VQ scan.
Tests that may be done
- Ventilation scan: you breathe in a gas or aerosol containing a tiny amount of radioactive tracer.
- Perfusion scan: you receive an injection of a radioactive tracer into a vein in your arm.
- Both scans take about 30–60 minutes total.
What to expect at your appointment
You will lie on a table while a special camera (gamma camera) takes pictures from different angles. The test is painless. You can eat and drink normally beforehand. After the scan, you can go back to your usual activities. The radioactive tracer leaves your body naturally within a few hours.
Treatment
Treatment depends on what the VQ scan shows. If it detects a blood clot, the main treatment is medication to thin the blood and prevent new clots. If the scan is normal, no treatment for a clot is needed.
Self-care at home
- If you have a clot, take all medications exactly as prescribed.
- Stay active – gentle walking can help blood flow.
- Wear compression stockings if your doctor recommends them.
Medical treatments
Blood-thinning medications (anticoagulants) are the standard treatment for pulmonary embolism. These are usually given as injections or tablets for at least 3–6 months. In some cases, clot-dissolving drugs (thrombolytics) may be used in hospital for larger clots. Always follow your doctor’s advice on which treatment is right for you.
When is surgery considered?
Surgery is rarely needed. In very severe cases, a procedure called embolectomy (surgical removal of the clot) may be considered, or a filter placed in a large vein to catch clots.
Living with this condition
After a pulmonary embolism, most people recover fully. You may feel tired for a few weeks. Take things slowly and rest when needed. Your doctor will tell you when you can return to work, exercise, and normal activities.
Lifestyle tips
- Stop smoking – it greatly reduces your risk of future clots.
- Stay at a healthy weight.
- Move regularly – avoid sitting for long periods without getting up.
- Stay hydrated.
Diet and exercise
A heart-healthy diet (fruits, vegetables, whole grains, lean protein) can help. Gentle exercise like walking or swimming is encouraged after your doctor says it’s safe. Avoid vigorous activity until your symptoms have resolved.
Mental health and emotional wellbeing
A blood clot can be frightening. It is normal to feel anxious or worried about it happening again. Talk to your healthcare team about your concerns. They can offer support and resources.
Prevention
Many blood clots can be prevented. If you are at high risk (e.g., after surgery or long travel), your doctor may recommend blood-thinning medication or compression stockings. Staying active and hydrated also helps.
Screening programmes
Routine screening for clots is not recommended for most people. If you have a strong family history of clots, your doctor may suggest genetic testing or discuss preventive measures.
Complications
If left untreated
- An untreated pulmonary embolism can cause lasting damage to the lungs (pulmonary hypertension).
- It can also lead to heart failure or death in severe cases.
Long-term outlook
With prompt diagnosis and treatment, the outlook for pulmonary embolism is very good. Most people recover fully. The VQ scan helps doctors make the right diagnosis quickly, which greatly improves outcomes.
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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.