title: 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.
authors: Clinical Epidemiology Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, CT, USA. carlos.fragoso@yale.edu
authors: Carlos A
authors: CA
authors: Vaz Fragoso
authors: Thomas M
authors: TM
authors: Gill
authors: Gail
authors: G
authors: McAvay
authors: Peter H
authors: PH
authors: Van Ness
authors: H Klar
authors: HK
authors: Yaggi
authors: John
authors: J
authors: Concato
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