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Related Concept Videos

Pulmonary Function Tests01:25

Pulmonary Function Tests

Pulmonary Function Tests (PFTs)
Pulmonary Function Tests are crucial diagnostic tools for assessing respiratory function, particularly in patients with chronic respiratory disorders. They comprehensively evaluate lung volumes, ventilatory function, breathing mechanics, diffusion, and gas exchange. These tests help diagnose pulmonary diseases and play a significant role in monitoring disease progression, evaluating disability, and assessing response to therapy.
PFTs involve using a spirometer, a...
Chronic Obstructive Pulmonary Disease-IV: Assessement and Diagnostic Studies01:27

Chronic Obstructive Pulmonary Disease-IV: Assessement and Diagnostic Studies

Assessing and diagnosing Chronic Obstructive Pulmonary Disease (COPD) involves a detailed approach that includes a comprehensive review of medical history, physical examination, and a variety of diagnostic tests. This thorough evaluation is essential to ensure an accurate diagnosis and guide effective management strategies.
Medical History
Chronic Obstructive Pulmonary Disease-I: Introduction01:20

Chronic Obstructive Pulmonary Disease-I: Introduction

Chronic Obstructive Pulmonary Disease (COPD) is a long-lasting respiratory condition requiring continuous attention and care. It is a progressive lung disease that leads to breathing challenges due to airflow obstruction. It manifests as persistent respiratory symptoms and restricted airflow resulting from abnormalities in the airways and alveoli, usually due to long-term exposure to harmful particles or gases. COPD mainly consists of two primary conditions: emphysema and chronic bronchitis.
Introduction to z Scores01:05

Introduction to z Scores

A z score (or standardized value) is measured in units of the standard deviation. It indicates how many standard deviations the value x is above (to the right of) or below (to the left of) the mean, μ. Values of x that are larger than the mean have positive z scores, and values of x that are smaller than the mean have negative z scores. If x equals the mean, then x has a zero z score. It is important to note that the mean of the z scores is zero, and the standard deviation is one.
z scores help...
Introduction to z Scores01:06

Introduction to z Scores

A z score (or standardized value) is measured in units of the standard deviation. It tells you how many standard deviations the value x is above (to the right of) or below (to the left of) the mean, μ. Values of x that are larger than the mean have positive z scores, and values of x that are smaller than the mean have negative z scores. If x equals the mean, then x has a zero z score. It is important to note that the mean of the z scores is zero, and the standard deviation is one.
z scores help...
Respiratory Volumes01:15

Respiratory Volumes

Respiratory volumes are crucial metrics, meticulously measured to quantify the air exchanged in and out of the lungs during various phases of the breathing cycle. These precise measurements are vital for assessing lung function, diagnosing respiratory conditions, and monitoring overall respiratory health. Each parameter provides specific insights into the mechanics of breathing and the functional capacity of the lungs.
Tidal Volume (TV) Tidal volume (TV) is the air inhaled or exhaled in a...

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Employing the Forced Oscillation Technique for the Assessment of Respiratory Mechanics in Adults
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Z-scores for Spirometry Interpretation: Implications for Classifying Impairments in Lung Function.

J Henry Brems1,2, Sarath Raju1, Nirupama Putcha1

  • 1Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD.

Annals of the American Thoracic Society
|June 9, 2026
PubMed
Summary
This summary is machine-generated.

New spirometry guidelines using z-scores reclassify lung function severity. This shift particularly impacts COPD patients, often to a less severe category, correlating with reduced health risks.

Keywords:
COPDSpirometrypercent predictedz-scores

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Area of Science:

  • Pulmonary Medicine
  • Diagnostic Spirometry
  • Clinical Interpretation

Background:

  • Recent spirometry interpretation guidelines advocate for z-scores over percent-predicted values for classifying lung function impairment severity.
  • The clinical implications of adopting z-scores for spirometry interpretation remain largely unexamined.

Purpose of the Study:

  • To determine the proportion of individuals whose lung function severity classification changes when transitioning from percent-predicted values to z-scores.
  • To assess the association between altered severity classifications and respiratory symptoms, as well as clinical outcomes.

Main Methods:

  • Two cohorts were analyzed: NHANES III participants and patients with COPD from Johns Hopkins Health System.
  • Individuals were classified using both percent-predicted and z-score thresholds based on FEV1, categorizing them as normal, mild, moderate, or severe.
  • Changes in classification (less severe, more severe, unchanged) were evaluated for associations with symptoms (dyspnea, cough, etc.) and outcomes (mortality, exacerbations, hospitalizations) using regression analyses.

Main Results:

  • The analysis included 14,863 (NHANES) and 14,238 (COPD) individuals.
  • Z-scores led to reclassification to a lesser severity in 10% of the NHANES cohort and 49% of the COPD cohort; no individuals were reclassified to a higher severity.
  • Reclassification to a lesser severity was associated with a reduced risk of dyspnea, mortality, COPD exacerbations, and other outcomes, excluding cough.

Conclusions:

  • Transitioning to z-scores for spirometry interpretation significantly reclassifies lung function severity, especially in COPD patients.
  • Individuals reclassified to a lesser severity using z-scores exhibit a lower risk of clinically significant outcomes.
  • These findings support the adoption of z-score thresholds for more accurate spirometry interpretation and risk stratification.