Interpreting Lung Function Tests

A Step-by Step Guide

Bruce R. Thompson, Brigitte M. Borg, Robyn E. O'Hehir

• Publisher: Wiley-Blackwell
• Year: 2014
• ISBN:
  9781118405468
• Edition: 1
• Topic: Medicine
• Subtopic: Pulmonary & Thoracic Medicine

Lung function assessment is the central pillar of modern respiratory diagnosis, providing invaluable information to assist in clinical decision making and management strategies. Interpreting Lung Function Tests: A Step-by Step Guide is a practical "how-to" training manual, which provides the reader with the necessary skills to interpret lung function test results, and to write a concise and informative report on the outcome.

Interpreting Lung Function Tests: A Step-by Step Guide

• provides unique guidance on the reporting of pulmonary function tests, including illustrative cases and sample reports.
• utilizes the many references available on interpretation of lung function and provides a teaching/reference tool for report writing of lung function results routinely performed in clinical practice.
• provides the reader with the skill to interpret and write a concise, yet informative report
• provides examples of results and written reports (with commentary where necessary as further explanation).
• focuses primarily on tests performed as part of routine clinical testing: spirometry, static lung volumes, gas transfer, bronchial provocation tests, and maximal respiratory pressures.

Interpreting Lung Function Tests: A Step-by Step Guide is a superb new resource to educate medical students, junior doctors, family physicians, as well as advanced trainee physicians specializing in respiratory medicine, respiratory scientists, and respiratory physicians

Chapter 1
General features of interpretation and report writing

There are features in the interpretation of lung function tests and report writing that are common to most tests of lung function. This chapter explores these general features.

General features of interpretation

The general features of interpretation are (1)

1. assessing test validity;
2. assessing the adequacy of reference values for the particular subject;
3. determining normality or abnormality using upper and/or lower limits of normal;
4. classifying detected abnormalities based on known patterns of disease;
5. determining the severity of an abnormality;
6. comparing current and previous results to identify significant changes over time;
7. attempting to address clinical question(s) mentioned in the referral.

Assessing test validity

• Interpretation of results should begin with a review of test quality. Good test quality is important as suboptimal quality tests may impact negatively on the interpretation of results and hence on clinical decision making. Information regarding indicators of test quality is provided in the test-specific chapters and in Chapter 7.
• The identification of suboptimal quality results can be gleaned from examination of the raw test data, technical comments provided by the test operator or a combination of both.
• When a suboptimal quality test is obtained, a cautionary statement identifying the magnitude and direction of the impact of the suboptimal quality results should be included in the report. For example:

Results should be interpreted with caution as test performance for spirometry was suboptimal due to coughing at end expiration, and may result in potential underestimation of forced vital capacity (FVC).

Assessing the adequacy of reference values for the particular subject

• Lung function results are interpreted by comparing the obtained results to a known reference range.
• The reference range/equations chosen need to reflect the population(s) tested and the test methods used in the laboratory (1).
• The reference range used for each test, as well as the limits of the variables (e.g. age, height, weight) of the reference equations, should be known to those reporting.
  If reference values are extrapolated beyond the limits of the variables (for example, a subject's age is 85 years, but the age range of the reference set used is 8–80 years), then a cautionary statement should be included as there is uncertainty regarding the validity of the reference data. For example: Reference values for spirometry have been extrapolated for age and should be used with caution.
• Lung function may be affected by race. Clear differences between Caucasian and African-American populations in the United States have been shown (2). Ideally, the subject's race (or the race they identify within the case of mixed race) should be taken into account in selecting appropriate reference sets. There are, however, practical issues in identifying and using appropriate reference sets for multiple races, and appropriate reference sets for some tests do not exist.
  The Global Lung Initiative has published a multiethnic set of spirometry reference values (3), which goes some way to addressing the issue of race in reference values. At the time of writing, the Global Lung Initiative is working towards race-specific reference values for T_LCO also.
  A useful, but less than ideal solution for this problem, is the application of a race correction factor (e.g. 0.88 for FEV₁ and FVC (forced vital capacity)) to Caucasian reference values when testing non-Caucasian subjects (1). This method is by no means ideal and when a correction factor is applied, a cautionary statement should be used to inform the reader that the reference values have been adjusted for race. For example: Reference values have been adjusted for race and should be used with caution.

Determining normality or abnormality using upper and/or lower limits of normal

The normal range

• The normal range is defined by the range in which there is confidence for inclusion of 95% of the normal population.
• The 95% confidence limits are determined using the mean predicted value (MPV) calculated from the reference equations and the residual standard deviation (RSD) that d...