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The risk of pulmonary embolism (PE) is nearly four times higher in asthma patients than in the general population, European researchers report.
An expert not involved in their study, Dr Anetta Undas, said that based on the new findings and earlier research, pulmonary embolism should be ruled out when asthma patients don't respond well to therapy.
Dr Undas, from Jagiellonian University School of Medicine, Krakow, Poland, has reported before on links between atopic diseases and venous thromboembolism. "In clinical practise such patients should be monitored to diagnose venous thromboembolism promptly," she said.
"From my experience the prevalence of VTE in asthma is under diagnosed, since dyspnoea is perceived as a sign of asthma," Dr Undas said. "Asthma patients who respond to the current therapy suboptimally should be considered as having PE, and CT of the chest should be taken into account in clinical work-up. All severe asthma patients immobilised during exacerbations, especially if they receive steroids, are obese, or have family history of VTE, should receive thromboprophylaxis."
Patients with asthma have procoagulant and antifibrinolytic activity in their airways, leading the authors of the new study to look for a link with thromboembolic events.
Using data from three Dutch tertiary asthma clinics, Dr Christof J Majoor from Academic Medical Center, Amsterdam, The Netherlands and colleagues identified 648 outpatients with mild-moderate and severe asthma.
What the study found
The incidence of venous thromboembolism per 1 000 patient-years was 0.95 in patients with mild-moderate asthma, 1.29 in patients with severe asthma, and 0.46 in a sample selected from the general population of Norway, the research team reported.
The incidence of PE per 1 000 person-years was 0.33 in patients with mild-moderate asthma and 0.93 in patients with severe asthma, compared with only 0.18 in the general population. This translates into a 3.97-fold increase in PE risk for patients with mild-moderate asthma and an 8.93-fold increased risk in patients with severe asthma, the authors say.
In contrast, the risk of deep vein thrombosis (DVT) was not significantly higher in asthma patients, although the rates were numerically higher for patients with mild-moderate asthma (0.61) and severe asthma (0.36) than for the general population (0.28).
In multivariate Cox regression analysis, severe asthma and oral corticosteroid use were the only factors significantly associated with PE, whereas only body mass index was associated with DVT risk.
"Doctors should therefore increase their awareness and lower the threshold for the evaluation of patients with severe asthma for possible pulmonary embolism," the researchers conclude. "In addition, we believe that strategies to reduce the risk of pulmonary embolism, such as thromboprophylaxis, may be considered in patients with prednisone-dependent asthma."
Dr J D de Boer, also from Academic Medical Center, did not participate in this research, but has studied asthma and coagulation. He said, "I think that this article is of major importance for this field and has drawn our attention again on dysregulation of coagulation in asthma patients. We should better clarify the pathophysiology that is leading to this dysregulation."
"Allergic lung inflammation is characterised by dysregulation of pulmonary coagulation, yet we do not understand this well enough," Dr de Boer said. "It is of high interest trying to improve local coagulation parameters and see if this would beneficially alter lung inflammation. The activated protein C system and protease activated receptors are interesting cross-bridging mediators in (allergic lung) inflammation and coagulation and may further clarify altered coagulation parameters in asthma."
Dr Majoor did not respond to a request for comments about this report.
(Reuters Health, January 2013)
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