Deep Vein Thrombosis (DVT) and Lab Testing

What is Deep Vein Thrombosis (DVT)? It happens when a blood clot forms in a vein. DVTs mostly occur in a deep vein in the thigh or calf. Additionally, they can occur in deep veins in other parts of the body like arms, abdomen, or pelvis. These clots slow or block blood from returning to the lungs and heart by restricting the flow of blood.  

Clots occur easily in some people than others. Excessive blood clotting disorders can lead to the occurrence of DVTs. Pre-existing conditions, lifestyle choices, or medications increase the risk of blood clots. It is rare to have a predisposition because of inherited genes.  

Deep Vein Thrombosis keeps growing if left untreated. If DVT continues to grow, it obstructs the vein and cause pain, discoloration, swelling, inflammation, and may lead to permanent damage.  An increased risk for another DVT and long-term complications, known as postthrombotic syndrome (PTS), can occur after treatment. After a DVT, PTS can lead to chronic symptoms, such as long-term swelling, aching, pain, tiredness, heaviness, darkened skin, cramping, non-specific discomfort, or bluish tinge in the affected areas like arm or leg.  

However, the clot in its original location is not the greatest danger with DVT. The greatest danger is the risk of thromboembolism, which happens when a blood vessel is obstructed in a different part of the body. Pulmonary embolism (PE) occurs when part of a blood clot blocks blood flow to the lungs by breaking off and traveling to the lungs. PE is a medical emergency because it threatens life.  

Both PE and Deep Vein Thrombosis do not form in arteries, but they form in the body’s veins. So, they are grouped into venous thromboembolism (VTE). According to the Centers for Disease Control and Prevention (CDC), VTE affects around 900,00 people in the United States. Also, VTE kills 60,000 to 100,000 of the people affected, but most people die from PE. The first symptom of around 25% of people with PE is sudden death.  

DVT causes long term complications in around 30-50% of those with DVT. DVT and/or PE will occur within ten years in about 30% of people.  

Risk Factors 

Some conditions and factors increase the risk of DVT. For people with one or more conditions or factors, this increases their risk. And the resulting risk is cumulative. For instance, having an inherited risk increases the risk if the person uses oral contraceptives or smokes.  

You are not born with the most common risk factors. You acquire them later in life. Making changes can help lower the risk of blood clots in some of these factors.  

Here are some of the acquired risk factors:

  • Age – as you get older, the risk of clots increases.  
  • Chronic conditions like lung disease, kidney diseases such as nephrotic syndrome, heart disease such as congestive heart failure, and recent or recurrent cancer.  
  • Placing catheter in a central vein – a tube, which is placed into the main vein of the body, is used to administer fluids and medications. It is usually used when DVTs occur in the upper body.  
  • Hormone estrogen increasing – Hormone estrogen increases during pregnancy and after three months of delivery, and it increases from medications such as hormone replacement therapy or estrogen-based birth control. 
  • Your history of DVT – Having a blood clot increases the risk of having another one.  
  • Immobility – sitting or staying in bed for a long period slows blood flow. Why? The calf muscles do not help in blood circulation because they do not contract. Venous stasis, which is also known as “coach-class syndrome,” happens when something slows blood flow for several hours. This usually happens when someone is put on prolonged bed rest or during a long plane ride.  
  • Surgery – orthopedic surgeries like knee or hip surgeries and surgery that involves the pelvis or abdomen may lead to an activation of tissue factors. Activation of tissue factors increases the risk of immobility during surgery and the risk of clotting.  
  • Staying in hospital – 50% of blood clots happen after surgery or after a hospital stay and when the person is staying in the hospital.  
  • Antiphospholipid syndrome (APS) – this is an excessive clotting disorder 
  • Inflammatory bowel disease 
  • Injury to the vein – blood clots are formed by an injury to the walls of veins. Muscle injuries, fractures, or other trauma can cause injury to the vein.  
  • Smoking  
  • Obesity 
  • It is rare for inherited genetic variations to increase the risk of inappropriate clotting. The following are the common inherited risk factors. 
  • Deficiency in protein S, protein C, or antithrombin  
  • Factor II mutation – prothrombin 20210 mutation 
  • Activated protein C resistance – Factor V Leiden mutation  

Signs and Symptoms  

More than half of people with DVT do not have noticeable signs and symptoms. Although some of these people have a few noticeable signs and symptoms, however, symptoms can develop suddenly or gradually if you do not have them.

Here are the signs and symptoms:

  • You will see swelling due to the buildup of fluid in the affected leg. 
  • You will feel pain or tenderness in the affected leg. If clots develop rapidly, it can cause more pain.  
  • You will see redness or warmth of the skin in the leg.  
  • The clot may break and travel to the lungs, causing a pulmonary embolism (PE). The signs and symptoms of pulmonary embolism can develop quickly. The following are the signs and symptoms of PE.  
  • Your chest pains worsen when you take a deep breath or cough  
  • You cough up blood  
  • You have difficulty breathing  
  • You experience fast or irregular heartbeat  
  • You may faint or have very low blood pressure  

Laboratory Tests 

Evaluation is done to estimate the probability of the person having DVT before doing a test. When doing an evaluation, there are so many factors, such as signs and symptoms and the person’s medical history, that are taken into consideration.  

Once the valuation is complete, a D-dimer test is first done if the person’s pre-test probability is low to medium. If the result of the D-dimer test is negative, it rules out a DVT. A DVT or any other conditioner causes a positive result. For diagnosis, this requires one or more imaging tests. 

D-dimer test is not done if the person’s pre-test probability is high for a DVT. In this case, one or more imaging tests are done.  

These are the steps from the American College of Physicians (ACP), the American Academy of Family Physicians (AAFP), and the American Society of Hematology (ASH).  

An initial evaluation can be done with some general laboratory tests. Here are some of the general laboratory tests that can be done with an initial evaluation.  

Complete blood count – the test is for evaluating blood components like cell fragments and platelets that help in blood clotting   

partial thromboplastin time (PTT) and prothrombin time (PT) – these tests are for evaluating the amount and function of the blood clotting factors.  

A person diagnosed with a DVT and does not have classic risk factors, or a person is under 50 years and has DVT, or the person in an unusual location needs more tests. Additional tests are used for determining the underlying cause. Also, these additional tests are for determining the risk of having recurrent DVTs.  

There following are the tests that are done when a person is being treated for a DVT:

Antiphospholipid antibodies like lupus anticoagulant – for diagnosing antiphospholipid syndrome (APS) 

Prothrombin 20210 mutation (factor II) and factor V Leiden – for detecting inherited risk factors. It is done if the person has a recurrent blood clot. It is not done during the first DVT.  

Treatment for a DVT and the existing blood clots can affect some tests. So, the only way to do these tests is by treating and resolving the clot. Therefore, healthcare practitioners determine the cause of a person’s DVT by ordering the following test several weeks or months later. The tests are used for detecting deficiency in blood clotting factors.  


Protein S and protein C  

Here are the tests for monitoring treatment:

PT/INR – the test is for monitoring warfarin therapy  

PTT – the test is monitoring standard heparin therapy  

Heparin anti-Xa – the test is for monitoring both standard low molecular weight heparin (LMHW) therapy and heparin therapy   

Warfarin sensitivity testing – the test is done when warfarin therapy is prescribed, and the test is for determining sensitivity and resistance to warfarin. And it helps healthcare practitioners in selecting appropriate doses.