Understanding the Causes and Risk Factors of Deep Vein Thrombosis
When explaining DVT to your patient, emphasize that blood clots form when three key conditions come together: slow blood flow, blood vessel injury, and increased clotting tendency—and most patients have multiple risk factors working together from different categories. 1
Three Main Categories of Risk Factors
Your patient's DVT likely resulted from a combination of factors across three categories that work together to increase clotting risk 1:
Patient-Related Factors (Personal Characteristics)
Age and Body Factors:
- Advanced age (over 60 years) increases DVT risk by about 34% and accounts for roughly 4% of overall risk 1, 2
- Obesity (BMI over 30) independently raises DVT risk 1, 2
- Male gender shows slightly higher rates in older age 3
Previous Clotting History:
- Prior DVT is the single strongest predictor—increasing risk 6-fold and representing about 23% of total risk 1, 2
- This makes recurrence prevention critically important 1
Inherited Blood Clotting Disorders:
- Inherited thrombophilia (protein C, protein S, or antithrombin deficiency) increases risk nearly 6-fold 1, 2
- Factor V Leiden mutation (affects ~5% of Caucasians) 2
- Prothrombin gene mutations 2
- Note: These inherited factors are less important in cancer patients 1
Common Medical Conditions:
- Active infection increases risk by 48% and contributes about 5% of total risk 1, 2
- Heart failure 1
- Kidney disease 1
- Pregnancy 1
Disease-Related Factors (Active Medical Problems)
Cancer is a Major Driver:
- Active cancer increases DVT risk 4- to 7-fold and causes approximately 20% of all community DVT cases 1, 2
- Highest-risk cancers include pancreatic, brain, lung, ovarian, kidney, stomach, bladder, and testicular tumors 1, 2
- Blood cancers (lymphoma, acute leukemia, multiple myeloma) carry particularly high risk 1
- Metastatic disease dramatically amplifies risk—nearly 20-fold compared to localized cancer 1, 2
- The first 3 months after cancer diagnosis represents peak thrombotic risk 2
Critical Illness:
- ICU admission increases risk 1.7- to 2.1-fold, contributing 6-14% of total risk 1, 2
- Poor performance status 1
Treatment-Related Factors (Medical Interventions and Immobility)
Immobility is Critical:
- Prolonged bed rest or immobility increases risk over 3-fold and accounts for 14% of overall risk 1, 2
- Hospitalization alone causes over 547,000 DVT cases annually in the US (239 per 100,000 hospitalized patients) 1, 2
- Acute paralysis (spinal cord injury) increases risk nearly 3-fold 1, 2
Surgical and Trauma Factors:
- Recent major surgery roughly doubles DVT risk in cancer patients and triples fatal PE risk 2
- Lower extremity fractures 2
- Pelvic fractures 4
- Traumatic injury, especially in patients over 60 2
Cancer Treatments:
- Active chemotherapy raises risk about 6.5-fold 2, 5
- Anti-angiogenic drugs (thalidomide, lenalidomide, bevacizumab) substantially increase risk 1, 2
- Hormonal therapies (tamoxifen, oral contraceptives, hormone replacement) elevate DVT incidence 1, 2
- Erythropoiesis-stimulating agents (ESAs) increase thrombotic risk 1, 2
Indwelling Devices:
- Catheters, pacemakers, and defibrillators put patients at highest risk for upper-extremity DVT 1
Laboratory Warning Signs
Your doctor may have noticed these blood test abnormalities that predict DVT risk:
- Elevated platelet count (thrombocytosis) before chemotherapy 1, 2
- High white blood cell count (leukocytosis) 1, 2
- Low hemoglobin (anemia below 10 g/dL) 1
- Elevated D-dimer and fibrinogen levels 2
- Elevated C-reactive protein 2
Key Clinical Considerations
Common Pitfalls to Avoid:
- DVT risk factors rarely occur in isolation—most patients have multiple contributing factors from all three categories 1
- In cancer patients, hospitalization combined with active disease creates particularly high risk 1
- Recurrence risk is substantially higher in cancer patients (21% vs 7% at 12 months) compared to non-cancer patients 1
Understanding Your Personal Risk: