Are people with autoimmune diseases more prone to blood clots?
People admitted to hospital with a wide range of immune-mediated diseases, especially lupus and polyarteritis nodosa, later had clearly higher rates of blood clots in the veins than a comparison group.
Source
Risk of venous thromboembolism in people admitted to hospital with selected immune-mediated diseases: record-linkage study
Study at a glance
- Design
- Cohort — Retrospective record-linkage cohort study in three hospital datasets (Oxford 1963-1998, Oxford 1999-2008, all of England 1999-2008), comparing age-, sex-, year- and area-standardised VTE rates after admission for each immune-mediated disease with a reference cohort admitted for minor conditions.
- N
- No single N: disease cohort sizes are given in a table not included in the text; reference cohorts had 313,716 (ORLS1), 187,609 (ORLS2) and 3,707,315 (England) people. The England multiple sclerosis cohort alone had 81,950 people.
- Population
- People admitted to NHS hospitals (or day-case care) in the Oxford region and England with one of many immune-mediated diseases, versus people admitted for mainly minor medical and surgical conditions
- Outcome
- Subsequent hospital admission for, or death from, venous thromboembolism (deep vein thrombosis or pulmonary embolism), as a standardised rate ratio
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Using linked hospital and death records from the Oxford region (two time periods) and from all of England, the researchers built cohorts of people at their first admission for each of many immune-mediated diseases, such as rheumatoid arthritis, lupus and multiple sclerosis. They compared how often these people were later admitted with, or died from, venous thromboembolism against a reference cohort admitted for mainly minor conditions. Rates were standardised for age, sex, year, area and, in England, deprivation, and risks within 90 days and after 90 days were compared.
What they found
Many diseases, including type 1 diabetes, multiple sclerosis, psoriasis, rheumatoid arthritis and lupus, showed raised VTE risk in all three datasets, and more showed raised risk in the larger England data. Lupus had the highest risk, about 3.61 to 4.60 times the reference rate, with polyarteritis nodosa similarly high. Where numbers allowed, the raised risk persisted beyond the first 90 days after admission. In England, about 1.8% of the multiple sclerosis cohort and 2.7% of the lupus cohort had a VTE admission during the study period.
The limits
What it doesn't show
The authors call the study exploratory: it used routine administrative data with no clinical, laboratory or treatment information, and no data on smoking or ethnicity, so drugs such as corticosteroids, immobility or disease severity could explain the link. Only hospitalised patients were included, likely the more severe cases, and cohorts began at first recorded admission rather than diagnosis. Many diseases were tested, so some weaker associations could be chance findings, and the huge England dataset made even small differences significant.
Key terms
- Venous thromboembolism (VTE)
- A blood clot in the veins, covering deep vein thrombosis (usually in the leg) and pulmonary embolism (a clot that travels to the lungs).
- Record-linkage study
- A study that joins separate routine records, such as hospital admissions and death certificates, for the same individuals over time.
- Rate ratio
- The event rate in an exposed group divided by the rate in a comparison group; here, after standardising for age, sex and other factors.
- Indirect standardisation
- Applying stratum-specific rates from a standard population to each group's make-up to compare groups fairly across age, sex and other strata.
- Thromboprophylaxis
- Measures, usually anticoagulant drugs or compression, given to prevent blood clots in people at risk, such as hospital patients.
- Virchow's triad
- The three classic contributors to venous clots: slowed blood flow, blood that clots more easily, and damage to the vessel wall.
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Quiz yourself
What type of study is this?
Common questions
Why compare with other hospital patients rather than the general public?
Everyone in the datasets had been admitted to hospital, so using a reference cohort admitted for a diverse range of minor conditions from the same database helps cancel out effects of hospitalisation itself, area and recording practices.
How could inflammation lead to clots?
Inflammation alters the lining of blood vessels and raises clotting factor levels, touching two parts of Virchow's triad. Immobility and treatments like corticosteroids could also contribute, and this study cannot separate these routes.
Should every patient with an autoimmune disease get anticoagulants?
No. The authors suggest considering thromboprophylaxis during admission, especially for high-risk diseases such as lupus and polyarteritis nodosa, but note the risk is still at least an order of magnitude lower than after surgery.
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