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Fixed ratio yields higher rate of airflow limitation diagnosis in elderly patients

A fixed-ratio criterion was more likely to yield a diagnosis of airflow limitation in elderly patients than was a lower limit of normal value criterion, according to recent research.

“As expected, the incidence rate is consistently higher when using the fixed-ratio criterion rather than the [lower limit of normal value (LLN)] criterion and there are effects of age and smoking,” Johannes A. Luoto, of the department of health sciences and division of geriatric medicine at Scania University Hospital and Lund University in Malmö, Sweden, and colleagues wrote. “This would imply that in a geriatric population higher age and active smoking habits are independent risk factors for developing COPD even when LLN criteria are used.”

The researchers compared measurements of airflow limitation using LLN and fixed-ratio spirometric criteria in 984 participants — with an acceptable spirometry — aged between 65 years and 100 years, according to the abstract. They defined airflow limitation as both the ratio of forced expiratory volume in 1 second and forced vital capacity of less than 0.7 and less than LLN.

Using a fixed-ratio criterion, the incidence of airflow limitation was 1.41-fold higher than using LLN (28.2 per 1,000 person-years vs. 11.7 per 1,000 person-years), according to the abstract. Further, using a fixed-ratio criterion, age significantly increased the incidence of airflow limitation, but the increase was less significant using LLN.

The likelihood of 5-year mortality increased when using LLN vs. fixed-ratio.

Luoto and colleagues also noted a higher incidence of COPD in women recruited to the study.

“A potential sex effect for LLN incidence has, at least partially, been observed previously for younger subjects, and previous studies have suggested that females may be more susceptible to tobacco smoke than males,” Luoto and colleagues wrote. “Other potential mechanisms behind the sex effect may include effects of sex hormones, susceptibility due to dimensional differences and morphological differences suggesting a difference in the natural history of COPD.” – by Jeff Craven

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