Predicted values are used in spirometry to compare the actual total volumes breathed out during the test with an average of the normal total volume for a person with the same personal stats of birth sex, ethnicity, height, weight, and age.
There are 5 different predicted value reference points we use that come from research with different scopes and goals: Quanjer 2012 (GLI 2012), NHANES III 1999 (Hankinson), ERS 1993, Crapo 1981, and Knudson 1976.
The importance of predicted values in interpreting spirometry results
Predicted values are an important comparison point when it comes to evaluating results. Because the calculations of the predicted values are done using data from research with substantial sample sizes, the predicted values and looking at where the results of the particular subject fall among those tell the healthcare team a great deal about the state and the capacity of the lungs.
How do these predicted value references differ from each other?
Quanjer 2012 (GLI 2012)
These references come from the European Respiratory Journal paper named Multi-ethnic reference values for spirometry for the 3–95-yr age range: the global lung function 2012 equations, prepared by the ERS Task Force.
The goal of the Task Force was to derive globally applicable continuous prediction references and their lower limits of normal. The data used (collected from around 100000 people) was shared with the ERS from 72 centers in 33 countries.
Using the data, references for healthy, nonsmoking people between the ages of 3 and 95 were created (around 57000 Caucasians, 3000 African-Americans, 5000 North East Asians, 8000 South East Asians).
FEV1 and FVC between ethnic groups differed proportionally enough to ensure that FEV1/FVC remained virtually independent of ethnicity.
These predicted values entail FEV1, FVC, FEV1/FVC, FEF25-75, and FEF75 values.
NHANES III 1999 (Hankinson)
The reference values in this case come from the third National Health and Nutrition Examination Survey (NHANES III) conducted from 1988 to 1994. The survey includes around 7500 healthy, non-smoking Caucasian, African-American and Mexican-American participants between the ages of 8 to 80. The participants consisted of a random sample of the nonsmoking U.S. population living in households, from 81 different counties.
NHANES III used the equipment and procedures that met the 1987 American Thoracic Society's spirometry recommendations. After the revised 1994 document came out just as NHANES III was completing data collection, to account for the changes in extrapolated volume and the reproducibility criteria, the raw data were also reanalyzed.
The participants completed a detailed administered questionnaire that gathered information on sex, race, ethnicity, health, and limited occupational history. Body measurements were also taken, including standing height, weight, and sitting height.
In the test, each subject attempted to perform at least five FVC maneuvers, with an additional goal of meeting the ATS acceptability and reproducibility criteria.
The reference equations were generated using data collected from three race/ethnic groups across a wide range of ages and geographic locations within the United States, and the quality control process and the compliance with ATS recommendations ensured that the results would be useful for diagnostic and research purposes.
These predicted values entail FEV1, FEV6, FVC, PEF, and FEF25-75 values.
ERS 1993 (Quanjer 1993)
The study was a product of European Community for Steel and Coal, and the standards mentioned are a reflection of what would be considered normal for the average steel and/or coal worker.
In the study, the lung volumes are subdivided into static and dynamic
lung volumes. The factors which determine the size of the normal lung for static lung volume include stature, age, sex, body mass, posture, habitus, ethnic group, reflex factors and daily activity patterns.
For the dynamic lung volumes, determining factors are the ability to move air rapidly in and out of the lungs, and any ventilatory impairment can arise from changes in the nervous system, the skeleto-muscular system, the skin and subcutaneous tissues, the lungs or the inhaled gas.
Reference values for lung volumes and forced ventilatory flows for adults of European descent are derived from studies carried out on subjects who were nonsmokers without (previous) disease which could compromise their ventilatory function.
These predicted values entail IVC, FVC, TLC, RV, FRC, RV/TLC, FRC/TLC, FEV1, FEV1/FVC, FEF25-75, PEF1, MEF75, MEF50, and MEF25 values.
Forced expiratory volumes and flows were measured in 251 healthy nonsmoking men and women using techniques and equipment that meet American Thoracic Society (ATS) recommendations in the study "Reference Spirometric Values Using Techniques and Equipment that Meet ATS Recommendations".
Each volunteer filled out a questionnaire, was examined by a pulmonary physician, and received a chest radiograph. The subjects used were lifetime nonsmokers (total of less then .5 packs a year and no smoking in the previous 6 months) and had no symptoms of lung, heart or chest wall disease, and their physician exam and radiograph were clear.
Subjects were weighed and measured in indoor clothing without shoes, and age was recorded to the nearest birthday. They consisted of a total of 126 women and 125 men and each age decade between the ages of 15 to 84 had an equal number of subjects.
The participants consisted greatly (around 90%) of Mormons and lived in 1400m altitude urban areas.
The study did not find that the addition of weight, body surface area, or transformations significantly improved the predictability of the regression equations using height and age alone.
The equations in this study were generated using the best test from three acceptable tracings. In the normal subjects of the study, there was no significant difference between selecting the largest FVC or FEV1 result or using the best test result.
These predicted values entail FVC, FEV0.5, FEV1, FEV3, FEF25-75, FEV1/FVC, and FEV3/FVC values.
In the study, a randomly selected population of 3115 people that represents the Caucasian population of Tuscon, Arizona were tested to gather flow-volume data. Of these, data from the 746 subjects who were totally free of symptoms or history of cardiorespiratory disease and who had never smoked were used in determining "normal" prediction equations for spirometric parameters and maximal expiratory flows.
Each subject that was 6 years or older performed at least 5 forced expiratory vital capacity (FVC) maneuvers. The utility of performing multiple tests of FVC was evaluated by examining, without regard to age, sex, or symptomatology, the FEV1 and FVC values obtained from all 3,115 subjects according to 3 criteria: (1) using the average values of the best 2 of 5 tests; (2) using the average of the best 2 of the first 3 tests; (3) using the single best value of the first 3 tests. Although both FEV1 and FVC initially increased and then decreased with age, the ratio of these 2 volume measurements tended to decrease consistently with age.
For this population sample defined as "normal," prediction equations were derived for flows at decile and quartile increments in 4 different age-sex groups, using age and standing height as independent variables.
These predicted values entail FEV0.5, FEV1, FEV2, FEV3, and FVC values.
- "Multi-ethnic reference values for spirometry for the 3–95-yr age range: the global lung function 2012 equations", European Respiratory Journal, 2012.
- "Spirometric Reference Values from a Sample of the General U.S. Population", American Journal of Respiratory and Critical Care Medicine, 1999.
- "Lung Volumes and Forced Ventilatory Flows",European Respiratory Journal, 1993.
- "Reference Spirometric Values Using Techniques and Equipment that Meet ATS Recommendations", American Review of Respiratory Disease, 1981.
- "The Maximal Expiratory Flow-Volume Curve - Normal Standards, Variability, and Effects of Age", American Review of Respiratory Disease, 1976.