Every year, venous thromboembolism — a category that includes deep vein thrombosis and pulmonary embolism — affects an estimated 900,000 Americans, according to the Centers for Disease Control and Prevention (CDC). It is one of the most preventable causes of hospital-related death, yet awareness of the biology behind clotting remains limited for most people outside of clinical settings.
Blood Clot Awareness Month, observed each March, is a dedicated opportunity to change that. Beyond recognising symptoms after the fact, there is real value in understanding the biological mechanisms that contribute to clot formation — and in knowing that coagulation activity can be measured and monitored through specific blood biomarkers.
This article is not about fear. It is about understanding how the body’s clotting system works, what markers are associated with that process, and how informed individuals can use biomarker awareness as part of a proactive approach to their health.
What Blood Clots Actually Are
A blood clot, or thrombus, forms when blood transitions from a liquid state to a solid or semi-solid mass. In normal physiology, this is a critical protective response — clots stop bleeding when a blood vessel is injured. The problem arises when clots form where they should not, or fail to dissolve properly after the threat has passed.
How Thrombosis Develops: Virchow’s Triad Explained Simply
Medical understanding of why abnormal clots form is often framed through a concept called Virchow’s Triad — three core contributing conditions identified in the 19th century that remain clinically relevant today.
The first is slowed or disrupted blood flow. When blood moves slowly through a vessel — during long periods of immobility, for example — it is more likely to pool and begin clotting. The second is vessel wall damage, which can occur from surgery, trauma, or chronic inflammation, triggering the clotting cascade even without active bleeding. The third is hypercoagulability, a state in which the blood is more prone to clotting than usual due to inherited traits, hormonal changes, cancer, or other systemic factors.
When two or more of these conditions are present simultaneously, the risk of abnormal clot formation increases meaningfully.
DVT vs. Pulmonary Embolism
Deep vein thrombosis (DVT) refers to a clot that forms in a deep vein, most commonly in the legs. Symptoms may include swelling, warmth, and aching in the affected limb — though DVT can also be entirely asymptomatic.
Pulmonary embolism (PE) occurs when a clot — often a fragment from a DVT — travels through the bloodstream and lodges in a pulmonary artery, obstructing blood flow to part of the lung. PE can be life-threatening and may present as sudden shortness of breath, chest pain, rapid heart rate, or dizziness. PE is a medical emergency requiring immediate care.
Together, DVT and PE are grouped under the term venous thromboembolism (VTE).
Why Blood Clot Awareness Month Matters
The Public Health Impact of Venous Thromboembolism
VTE contributes to an estimated 100,000 deaths in the United States each year, according to the CDC. It is the third most common cardiovascular diagnosis after heart attack and stroke. Despite this, public recognition of VTE risk factors and warning signs lags far behind awareness of those more well-known conditions.
The Surgeon General has previously issued a call to action on DVT and PE specifically because of the gap between the condition’s prevalence and the level of public awareness surrounding it. Blood Clot Awareness Month, championed by organisations such as the National Blood Clot Alliance (NBCA), aims to bridge that gap through education.
Who Is at Higher Risk?
Several circumstances and characteristics are associated with an elevated likelihood of VTE. These include recent surgery or hospitalisation, particularly with extended immobility during recovery. Long-distance travel — especially flights lasting more than four hours — is associated with increased clot risk due to prolonged sitting and reduced leg movement. Pregnancy and the postpartum period are high-risk times due to increased clotting factor activity and changes in blood flow dynamics.
Other factors include cancer and certain cancer treatments, hormone therapies including some oral contraceptives, obesity, older age, prior clot history, and inherited genetic variants that predispose individuals to hypercoagulability.
Key Biomarkers Linked to Clotting Activity
A range of laboratory tests is used to assess different aspects of the coagulation system. These biomarkers do not diagnose blood clots independently — but they offer measurable insight into how the clotting system is functioning and can support clinicians in evaluating individual risk profiles.
D-Dimer — A Marker of Clot Breakdown
D-dimer is a protein fragment produced when a blood clot dissolves. When clotting and clot breakdown (fibrinolysis) are occurring in the body, D-dimer levels in the blood tend to rise. This makes it a useful marker of clot-related activity.
It is important to understand what D-dimer can and cannot tell you. An elevated D-dimer does not confirm that a clot is present — it can be raised for many reasons, including recent surgery, infection, inflammation, pregnancy, or even vigorous exercise. A normal D-dimer result in a low-risk individual is considered more clinically informative than an elevated result alone. Diagnosis of DVT or PE requires imaging studies such as ultrasound or CT pulmonary angiography, interpreted by a clinician.
D-dimer is used in clinical settings primarily as part of a structured risk assessment, not as a standalone test.
Fibrinogen and Clot Formation
Fibrinogen is a protein produced by the liver that plays a central role in clot formation. When a vessel is injured, fibrinogen is converted into fibrin — the structural mesh that holds a clot together. Elevated fibrinogen levels are associated with increased clotting tendency and are also considered a marker of systemic inflammation.
Chronically elevated fibrinogen has been associated in research with heightened cardiovascular and thrombotic risk. Conversely, very low fibrinogen can impair the body’s ability to form clots when needed, increasing bleeding risk. Understanding one’s fibrinogen level provides a window into both clotting potential and the broader inflammatory environment.
PT/INR and aPTT — Measuring Clotting Time
Two commonly ordered tests measure how quickly the blood clots through different pathways.
Prothrombin time (PT) and its standardised expression as the International Normalised Ratio (INR) measure the time it takes for blood to clot via the extrinsic coagulation pathway. PT/INR is most commonly associated with monitoring patients on warfarin (a blood-thinning medication), but it also provides baseline information about how the clotting cascade is functioning.
Activated partial thromboplastin time (aPTT) assesses the intrinsic pathway of coagulation. It is sensitive to deficiencies in several clotting factors and is also used to monitor heparin therapy. Abnormal aPTT results can suggest inherited clotting factor deficiencies or the presence of lupus anticoagulant, an antibody associated with antiphospholipid syndrome and elevated clot risk.
Both tests are interpreted in context — a single result outside the reference range is a starting point for clinical investigation, not a conclusion.
Genetic Markers: Factor V Leiden and Prothrombin Mutations
Some individuals carry inherited genetic variants that make their blood more prone to clotting. The two most studied in this context are Factor V Leiden and the prothrombin G20210A mutation.
Factor V Leiden is the most common inherited thrombophilia in populations of European descent. It results from a mutation in the gene encoding clotting Factor V, making it resistant to a natural anticoagulant protein called activated protein C. Carriers of one copy of this mutation (heterozygous) have a moderately elevated lifetime risk of VTE; those with two copies (homozygous) face a substantially higher risk.
The prothrombin G20210A mutation leads to elevated levels of prothrombin in the blood, which is associated with increased clot formation activity. Like Factor V Leiden, it does not mean a clot will definitely occur — it indicates a biological predisposition that is meaningfully elevated relative to the general population.
Genetic testing for these markers can help individuals and their healthcare providers understand inherited background risk, especially in the context of high-risk situations such as pregnancy or surgery planning. A positive result indicates susceptibility, not certainty. Many carriers live their entire lives without experiencing a clot event.
What Clotting Biomarkers Can (and Cannot) Tell You
Screening vs. Diagnosis
A critical distinction for anyone exploring clotting biomarkers is the difference between awareness and diagnosis. None of the markers described above — D-dimer, fibrinogen, PT/INR, aPTT, or genetic testing — can diagnose a blood clot on their own. Diagnosis of DVT requires duplex ultrasound. Diagnosis of PE requires CT pulmonary angiography or a ventilation-perfusion scan. Both require clinical judgment and imaging, not laboratory results alone.
Biomarkers serve a supporting role. They provide measurable data that, when interpreted alongside symptoms, medical history, and physical examination, contribute to a more complete picture. They also help healthcare providers assess baseline clotting function, monitor individuals on anticoagulation therapy, and evaluate inherited risk before high-risk life events.
If you are experiencing symptoms of a possible clot — including sudden leg swelling, chest pain, or difficulty breathing — do not wait for lab results. Seek emergency medical care immediately.
Monitoring During High-Risk Periods
One of the more nuanced applications of clotting biomarkers is monitoring during periods of known elevated risk. For individuals recovering from surgery, travelling long distances, or navigating pregnancy, understanding where their clotting markers sit — and observing how they change — can support more proactive conversations with their healthcare team.
Serial monitoring does not replace clinical management, but it can help individuals feel more engaged with their biology during times when clot risk may be temporarily elevated. For people on anticoagulant therapy, regular PT/INR monitoring is already standard practice. For those not on therapy but with known risk factors, periodic awareness of markers like D-dimer or fibrinogen may prompt earlier clinical discussions.
Who May Benefit From Monitoring Clot-Related Biomarkers
Post-Surgery Recovery
Surgery — particularly orthopaedic procedures such as hip or knee replacement — carries a well-documented risk of postoperative DVT. Immobility during recovery, combined with the coagulation response to tissue injury, creates conditions closely aligned with Virchow’s Triad. Individuals in post-surgical recovery who are curious about their clotting markers may find value in discussing baseline and trending tests with their care team.
Frequent Long-Distance Travelers
Prolonged immobility in a seated position — on flights lasting four or more hours, or during long car or train journeys — is a recognised risk factor for DVT. This risk is sometimes referred to informally as “economy class syndrome,” though it is not limited to economy seating; the duration of immobility is the primary variable. Individuals who travel frequently for work or personal reasons may benefit from understanding their clotting biomarker baseline, particularly if other risk factors are also present.
Pregnancy and Postpartum
Pregnancy is associated with a natural increase in clotting factor activity — a physiological adaptation that reduces the risk of haemorrhage during delivery. However, this same hypercoagulable state elevates VTE risk throughout pregnancy and, importantly, during the six-week postpartum period. Women with a personal or family history of clotting disorders may particularly benefit from a discussion with their obstetrician or haematologist about clotting markers and inherited risk testing before or during pregnancy.
Individuals With Family History of Clotting Disorders
If a close family member — a parent or sibling — has been diagnosed with DVT, PE, Factor V Leiden, or another thrombophilia, there may be a meaningful inherited component to clot risk. Genetic testing for Factor V Leiden and the prothrombin mutation can help clarify whether that susceptibility is shared. This information is most valuable when used to inform clinical planning — not as a reason for anxiety, but as a piece of biological context that supports more informed health decisions.
Taking Ownership of Your Clot Risk Markers
How Direct-to-Consumer Testing Works
Direct-to-consumer (DTC) lab testing allows individuals to access certain blood tests without requiring a physician’s order. After selecting a test, the individual visits a certified local laboratory or collection point, provides a blood sample, and receives results through a secure digital platform — typically within a few days.
For clotting-related biomarkers, DTC options may include D-dimer, fibrinogen, PT/INR, CBC with platelet count, and in some cases genetic markers including Factor V Leiden. This kind of access supports health literacy by giving individuals data they can bring to clinical conversations, rather than waiting until a health event prompts formal evaluation.
DTC testing is a personal awareness tool. It does not replace clinical assessment, emergency care, or the management of known clotting disorders under physician supervision.
Tracking Biomarkers Over Time
The most meaningful use of biomarker data comes not from a single reading, but from observing patterns over time. Establishing a personal baseline for markers like D-dimer or fibrinogen — when you are well and not in a high-risk period — creates a reference point that gives future results more context.
If a result changes meaningfully over time, particularly during a period when risk factors are elevated, that shift becomes a useful prompt for a clinical conversation. Longitudinal tracking moves the experience from reactive to proactive — from waiting for a problem to present itself to actively engaging with the data your body is already generating.
The Role of Awareness Months in Preventive Health Literacy
Blood Clot Awareness Month is not just a symbolic occasion. It is a structured opportunity to raise the kind of biological literacy that genuinely supports better health outcomes — not by replacing clinical care, but by preparing individuals to engage with it more meaningfully.
VTE is one of the most preventable serious cardiovascular conditions. It is also one of the least discussed in everyday health conversations. Understanding what D-dimer measures, why fibrinogen matters, or what it means to carry a Factor V Leiden variant does not require a medical degree. It requires access to clear, accurate information and a framework for thinking about personal risk in a way that is empowering rather than frightening.
This March, consider what you know about your own coagulation health. If you have risk factors — a family history, a planned surgery, a frequent travel schedule, or a pregnancy — this awareness month is a fitting time to start that conversation with your healthcare provider. Bring data, ask questions, and approach your biology with curiosity rather than apprehension.
Proactive health ownership begins with understanding. Coagulation biomarker literacy is one important way to make that understanding concrete.
This article is for educational purposes only and does not constitute medical advice. Blood clot symptoms require immediate emergency medical attention — do not use biomarker testing as a substitute for urgent care. All laboratory results should be interpreted by a qualified healthcare professional in the context of a full clinical evaluation. Direct-to-consumer testing is a health awareness tool and does not diagnose, treat, or prevent any medical condition.
