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Rheumatology

Are people with autoimmune diseases more prone to blood clots?

Ramagopalan SV, Wotton CJ, Wotton CJ, et al. · BMC medicine · 2011

Open access · cc by · source: Europe PMC

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.

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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

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Key findings

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.

Methodology

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.

Limitations

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.

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