February 2017
Latest News

That Harmful Clot in Your Leg Veins: Understanding DVT

Dr Benjamin Chua
MBBS (S’pore) , MHsc(Duke), FRCSEd (Gen Surg)
Senior Consultant Vascular Surgeon and Medical Director
Vascular & Interventional Centre
Mt Elizabeth Novena Specialist Centre


This article appeared in the February 2017 issue of The Straits Times – Doctor-Is-In.



This is a condition in which blood clots form spontaneously in the deep veins of the lower or upper limbs. The deep veins of the limbs serve to carry de-oxygenated blood back to the heart and lungs. These veins are located near the major arteries of the limbs. It is more common to develop DVt of the lower limbs than upper limbs. Some underlying causes for the development of DVT include the following:

  • long-periods of immobility,
  • major surgery involving the limbs, pelvis or abdomen,
  • obesity,
  • dehydration,
  • major trauma or injury to the limbs.
  • an inheritable genetic pre-disposition to DVT due to the blood lacking the proteins to prevent spontaneous clotting or having excessive proteins that promote clotting,
  • abnormal blood vessel anatomy e.g May-Thurner syndrome or Paget-Schroetter Syndrome in which the draining veins of the limbs are compressed by either a neighbouring artery or by ribs in a tight space,
  • the presence of underlying cancer which can result in the blood in the veins being more prone to clotting (paraneoplastic syndrome), and
  • the “economy class syndrome” in which patients develop DVT of the legs after a long-haul flight. This results from a combination of immobility during the flight, sitting in cramped positions and dehydration in a pressurized plane cabin.



Most cases of DVT are fortunately not life-threatening and can be treated with medication. These are usually those cases with DVT involving the below knee segment of the legs or the forearm of the upper limb. However, patients with DVT extending above knee or upper arm towards the heart may be in greater danger as the clots in the DVT can break off in pieces and travel into the heart and lungs (embolize) resulting in a serious condition known as Pulmonary Embolism (PE) – this condition is life-threatening as it prevents oxygen transfer to the venous blood and is associated with significant risk of death.



Patients with DVT can present with a swollen and tender limb. In the legs, it may start in the calf and then extend towards the thigh and groin. In the upper limbs, it can start in the forearm and extend upwards.
Patients can also present with a fast heartbeat (tachycardia) and shortness of breath, either in isolation or related to the limb swelling. This is a worrying sign as it indicates the presence of Pulmonary Embolism.



To prevent DVT from “economy class syndrome”, travellers should keep well-hydrated by drinking lots of water during a long-haul flight. They should avoid excessive alcohol consumption and also avoid long-periods of immobility by getting out of the seat and walking around every 2 hours. The use of compression stockings during long-haul flights can also prevent the formation of DVT.
For patients about to undergo major limb, pelvic or abdominal surgery, prophylactic anti-coagulation (blood thinning) drugs can be given during the period before and after surgery. Sometimes, mechanical pumps that repeatedly compress on the calves at regular intervals can be applied to the patients throughout long surgery times.
If there is an underlying genetic pre-disposition to DVT, the patients may be started on long-term anti-coagulation drug therapy.



Diagnosis is based on a high index of suspicion – usually a positive risk factor history coupled with positive ultrasound scans showing the presence of clots in the deep veins. The scans can usually be done in the clinic. Other associated investigations include a CT scan of the pulmonary arteries and a ventilation-perfusion scan if there is a suspicion of PE.

Some other investigations that may be needed include a blood screen for pro-clotting factors and tumour markers if there is underlying suspicion of cancer.



The treatment of DVT depends on the severity of the disease as well as the underlying cause. All patients with DVT must be stated on blood thinning medication (anti-coagulation) unless there is a good reason to withhold it (e.g prone to bleeding in the gut or recent bleeding stroke in the brain). The objective of the anti-coagulation is to prevent more new blood clots from forming. The body usually helps in dissolving the existing vein blood clots over time, sometime up to 6 months. As such, all patients should be on the anti-coagulation medication during this period. In the interim, patients may sometimes be advised to wear leg compression stockings especially if they develop leg swelling.
If the DVT of the lower limb is extensive (e.g extending up the thigh and into the pelvic veins), it is sometimes necessary to use a combination of mechanical devices and special drugs to dissolve the clots. This process, known as thrombolysis, is usually done if the DVT is less than 2 weeks old and can be done via small groin vein punctures and under X-ray (fluoroscopy) guidance. It is recommended especially in cases where abnormal blood vessel anatomy is suspected as the cause i.e suspicion of the veins being compressed or narrowed by surrounding structures (May-Thurner syndrome). The thrombolysis is to prevent long-term problems associated with DVT such as chronic and repeated lower limb pain, swelling and formation of leg venous ulcers, a condition known as the Post-Thrombotic Syndrome (PTS. Aside from thrombolysis, metallic stents may be inserted at the narrowed part of the veins to keep them open.
For cases of upper limb DVT due to compression by surrounding structures (or Paget-Schroetter Syndrome), in addition to clot thrombolysis, it may sometimes be necessary to remove the 1st rib or surrounding muscle to reduce the tightness and compression of the upper limb veins as it travels in the region around the shoulder and clavicle.
In some cases, a metallic filter device that is able to trap loose clot fragments, may be inserted in the inferior vena cava (the largest vein in the abdomen, draining the leg veins towards the lung) to prevent clots that have broken off from the lower limb DVT from reaching the lung veins.
If a PE is detected, and there are severe symptoms of shortness of breath or chest pains with unstable blood pressure, emergency surgery may be needed to remove the blood clots in the lung through thrombolysis or open chest surgery.



Deep venous thrombosis is a highly preventable condition once patients are aware of the risk factors and take the necessary precautions. It also easily diagnosed by a simple examination and ultrasound scan. Effective treatment is also now widely available with good outcomes. Patients who suspect that they have a DVT should seek a vascular specialist referral for evaluation.



Dr Benjamin Chua is Senior Consultant Vascular Surgeon and Medical Director at the Vascular & Interventional Centre located at Mount Elizabeth Novena Specialist Centre. He is dedicated exclusively to the care of disorders of the circulatory system, primarily the arteries and veins. He provides comprehensive care for conditions affecting the arteries (aneurysms, PAD and carotid diseases) and veins (varicose veins, deep vein reflux and thrombosis) as well as vascular malformations and dialysis vascular access.

As a vascular surgeon, he is trained to perform all treatment options available to manage vascular diseases including medical management, minimally invasive procedures like angioplasty and stenting as well as traditional open bypass surgery and repairs His passion is in saving the limbs of diabetics with PAD as he feels that once their limbs are lost, it adversely affects their quality of life as well as that of their family members.