Photo Credit: Andrey Popov

A recent study suggests that the Late-Life Function and Disability Instrument is an effective diagnostic instrument to assess COPD disability and function.

While disability and loss of function are crucial problems for patients with chronic obstructive pulmonary disease (COPD), validated tools to assess them are lacking.

Astrid Blondeel, PhD, and coauthors addressed the gap in a paper for the Annals of the American Thoracic Society. Specifically, the researchers examined the Late-Life Function and Disability Instrument (LLFDI) to determine whether it could assess function and disability in COPD populations.

To assess the instrument’s validity, Dr. Blondeel and colleagues recruited 605 participants with COPD from six European countries. The researchers assessed the LLFDI’s validity based on participants’ self-reported answers.

Determining Assessment Criteria

Researchers originally designed the LLFDI for community-dwelling older adults, but they have validated it in other patient populations, including people with cardiovascular disease, stroke, osteoarthritis, and wheelchair users. However, the instrument’s validity in populations with COPD hasn’t been studied in detail.

To test LLFDI’s validity in populations with COPD, the researchers assessed the instrument based on four criteria:

• Ceiling and floor effects.
• LLFDI domain and subdomain scores’ distribution and levels.
• Construct validity, a confirmatory factor analysis of LLFDI’s structure.
• Known group validity, comparing self-reported answers to identified symptoms.

The researchers recruited participants from 13 sites in Belgium, Germany, Greece, Spain, Switzerland, and the United Kingdom. To be included in the study, participants had to be older than 18, have a COPD diagnosis, be clinically stable, and have a smoking pattern of at least ten packs annually. Exclusion criteria included an inability to walk four meters, mobility limitations unrelated to COPD, lung cancer diagnosis, and undergoing lung volume reduction surgery or lung surgery in the 6 months before the study.

The LLFDI comprises 64 items, divided into three domains (disability-frequency, disability-limitation, and function domains) and seven subdomains. Along with providing self-reported answers to the LLFDI, participants wore a sensor that monitored physical activity throughout the study.

Evaluating LLFDI’s Domains & Subdomains

The researchers found no floor or ceiling for the domains or subdomains, with two exceptions. The disability-limitation management subdomain had a ceiling effect, with 30% of patients reporting the highest score. The function upper limb subdomain had 23% of patients reporting the highest score.

The researchers also concluded that all LLFDI domains fit the model moderately. An even distribution of scores (on a scale of 1-100) for each domain and subdomain revealed this (Table).

Regarding convergent validity, the researchers determined weak to no correlation for the disability frequency domain, weak to moderate correlation for disability-limitation, and moderate correlation for function. Domain and subdomain scores had significantly lower values as COPD severity increased. However, the disability-frequency personal subdomain didn’t vary as severity increased. The researchers stated that the assessment tool had adequate convergent validity.

Criterion four, known groups validated, demonstrated similar results. The researchers analyzed the distribution of LLFDI scores among patient subgroups (defined by the GOLD stages I, II, III, and IV and GOLD classification A, B, and E) and by use of walking aid and age group. The LLFDI had good known group validity across domains.

The researchers concluded that there’s a range of functioning levels and disability in populations with COPD, though functioning levels decrease in older populations. The LLFDI captured this function and disability spectrum with a minimal ceiling effect and no floor effect. The researchers also validated it based on three additional criteria.

“The LLFDI is a valid instrument that can be used in people living with COPD to investigate disability and function,” the researchers concluded. “In doing so, the current practice of measuring physical functioning or objective outcomes can be enhanced by capturing information on disability and function in important life tasks from a patient-reported perspective.”