Status: Checked against official sources on 18 October 2026
FREQUENT FLYER GLOSSARY
What is deep vein thrombosis (DVT)?
Deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, most often in the leg, and it comes up in air travel because long stretches of sitting still slow the flow of blood through the legs. It is a medical condition rather than a ticketing or loyalty rule: risk depends on a person's own health factors, and the notes below are general information, not medical advice. Airlines and aviation regulators publish health material for passengers who want to prepare before they fly. [3] [5]
Facts checked: 18 October 2026
Key takeaways
- DVT is a clot in a deep vein, usually in the leg; it appears in travel-health material because immobility lets blood move more slowly through the legs.
- The UK Civil Aviation Authority (CAA) carries medical information and medical travel guidance within its air passengers section, alongside assisted-travel and accessibility content. [3]
- Qantas publishes fitness-to-fly policies for travelling with selected medical conditions, explains how to obtain medical clearance if one is needed, and offers inflight health information with inflight exercises. [5]
- This entry explains the term. It is not medical advice and does not assess whether any individual is fit to fly.
Why is DVT linked to long flights?
A deep vein thrombosis is a clot that forms in a vein deep inside the body rather than in the veins close to the skin. The deep veins of the leg are the usual site, and the reason air travel enters the same conversation is immobility: when the legs stay still for a long stretch, blood moves more slowly through them, and slow flow is one of the circumstances in which clots are more likely to form.
That is why passenger health material tends to talk about movement as well as about medical conditions. Qantas includes an inflight health section in its travel information, with useful information and inflight exercises intended to help minimise the impacts of flying. [5] The CAA routes passengers through an air passengers section that carries medical information and medical travel guidance next to its assisted-travel material. [3]
What such pages cannot do is give one answer for every traveller. A clot risk belongs to a person rather than to a cabin, so a clinician weighs a passenger's own medical history and health factors, and the outcome differs from one passenger to the next.
What does "fitness to fly" mean?
Fitness to fly is the part of an airline's travel information that sets out how passengers with a medical condition travel, and what clearance is required before boarding. Qantas states its policies for travelling with selected medical conditions, including COVID-19, and explains how to obtain a medical clearance if one is needed. [5]
Two details matter for anyone reading that policy with DVT in mind. The policy is written for selected conditions rather than for every diagnosis, so the airline's own list decides whether a condition falls inside it. [5] Clearance is also framed as something needed "if needed", which makes it condition-dependent rather than automatic for every passenger. [5] Because these are Qantas's policies, they govern travel with Qantas; a passenger booked on another carrier has to check that carrier's equivalent rules. [5]
The CAA's air passenger pages take a broader view, grouping medical information and medical travel guidance with assisted travel, accessibility rights, assistance dogs and help at the airport. [3] Passengers who will need help moving through the terminal can read more about mobility aid carriage.
How should you prepare if you are worried about DVT?
Begin with a clinician rather than with a booking. Whether a clot risk makes a particular flight advisable, and what to do about it, is a medical judgement about one person; this page only explains the term.
Then deal with the paperwork in good time. If the airline's fitness-to-fly policy covers your situation, medical clearance is obtained through the process the airline describes, and the trip is planned around it. [5] Passengers travelling while pregnant may also want the separate notes on pregnancy and air travel.
On board, the practical advice in airline health material centres on movement: Qantas's inflight health information includes inflight exercises aimed at minimising the impacts of flying. [5] Anyone who develops symptoms that worry them, during a flight or afterwards, should seek medical advice promptly rather than wait for the next trip. Jet lag is a different travel-health subject and is covered under jet lag.
Exceptions and limits
- Not medical advice. This entry explains a term. It does not diagnose or rule out DVT, recommend treatment, or state that any individual is fit to fly.
- One airline's policy is not another's. The fitness-to-fly policies described here are Qantas's and apply to travel with Qantas; other airlines publish their own rules for medical conditions and clearance. [5]
- Selected conditions only. Qantas's fitness-to-fly policies cover selected medical conditions rather than every condition, and clearance applies only where that policy requires it. [5]
- Regulator guidance has a jurisdiction. The CAA material sits in the UK authority's air passengers section; passengers elsewhere may be covered by a different authority's guidance. [3]
- Flight length is not the test. Immobility is the reason DVT is discussed in travel health, but no single flight duration settles whether travel is advisable for a particular person; that is a clinical judgement.
Frequently asked questions
Do I need medical clearance to fly with a history of DVT?
That depends on the airline's fitness-to-fly policy for the condition in question. Qantas sets out policies for travelling with selected medical conditions and explains how to obtain a medical clearance if one is needed. [5]
Where do UK passengers find medical travel guidance?
The UK Civil Aviation Authority's air passengers section carries medical information and medical travel guidance, alongside assisted-travel and accessibility content. [3]
Does Qantas suggest exercises during a flight?
Yes. Its travel information includes an inflight health section with useful information and inflight exercises intended to help minimise the impacts of flying. [5]
Is this page a substitute for medical advice?
No. Risk depends on individual health factors, and a clinician is the right person to assess them; this glossary entry explains what DVT is and how airline health guidance is organised.
Sources
Sources accessed on 18 October 2026. Guidance from other airlines and other national aviation authorities is not covered here.
- UK Civil Aviation Authority — air passengers: medical information and medical travel guidance, checked 18 October 2026
- Qantas — travel information: fitness to fly and inflight health, checked 18 October 2026