Use of Lambda-Mu-Sigma-Derived Z Score for Evaluating Respiratory Impairment in Middle-Aged Persons

Abstract

BACKGROUND:

The lambda-mu-sigma (LMS) method calculates the lower limit of normal for spirometric values as the 5th percentile of the distribution of Z scores. Conceptually, LMS-derived Z scores account for normal age-related changes in pulmonary function, including variability and skewness in reference data. Evidence is limited, however, on whether the LMS method is valid for evaluating respiratory impairment in middle-aged persons.

OBJECTIVE:

To evaluate the association of LMS-defined respiratory impairment (airflow limitation and restrictive pattern) with mortality and respiratory symptoms.

METHODS:

We analyzed spirometric data from white participants ages 45–64 years in the Third National Health and Nutrition Examination Survey (NHANES III, n = 1,569) and the Atherosclerosis Risk in Communities study (ARIC, n = 8,163).

RESULTS:

LMS-defined airflow limitation was significantly associated with mortality (adjusted hazard ratios: NHANES III 1.90, 95% CI 1.32–2.72, ARIC 1.28, 95% CI 1.06–1.57), and respiratory symptoms (adjusted odds ratios: NHANES III 2.48, 95% CI 1.75–3.51, ARIC 2.27, 95% CI 1.98–2.62). LMS-defined restrictive-pattern was also significantly associated with mortality (adjusted hazard ratios: NHANES III 1.98, 95% CI 1.08–3.65, ARIC 1.38, 95% CI 1.03–1.85), and respiratory symptoms (adjusted odds ratios: NHANES III 2.34, 95% CI 1.44–3.80, ARIC 1.89, 95% CI 1.46–2.45).

CONCLUSIONS:

In white middle-age persons, LMS-defined airflow limitation and restrictive-pattern were significantly associated with mortality and respiratory symptoms. Consequently, an approach that reports spirometric values based on LMS-derived Z scores might provide an age-appropriate and clinically valid strategy for evaluating respiratory impairment.