Table of Contents

Locator Record

Title: Exhaled Nitric Oxide (ENX_E )
Contact Number: 1-866-441-NCHS
Years of Content: 2007 - 2008
First Published: September, 2011
Revised: NA
Access Constraints: None
Use Constraints: None
Geographic Coverage: National
Subject:Fractional exhaled nitric oxide, ENO, FENO
Record Source: NHANES 2007 - 2008
Survey Methodology: NHANES 2007 - 2008 is a stratified multistage probability sample of the civilian non-institutionalized population of the U.S.
Medium: NHANES Web site; SAS transport files

Component Description

The measurement of Fractional Exhaled nitric oxide (FENO) was one of two NHANES 2007-8 examination components on respiratory health sponsored by the National Heart, Lung, and Blood Institute of the National Institute of Health. Spirometry, including a 2nd test post-Bronchodilator Spirometry was also conducted. Nitric Oxide (NO) is a chemical normally produced in the respiratory tract and can be detected in the exhaled breath. It is a noninvasive marker of airway inflammation. FENO has been shown to be higher in persons with asthma, chronic obstructive pulmonary disease (COPD) and other respiratory conditions as compared to levels found in healthy persons. FENO measurements have also been used as a tool to monitor compliance with treatment with inhaled steroids in asthmatics.

The objective of the nitric oxide data collection was to produce baseline FENO measurements and reference ranges for the U.S. healthy population as well as those with asthma and COPD, and those who are smokers. The data collection was also intended to help define the prevalence of undiagnosed airway inflammation in the US, and to examine the association between airway inflammation, other measurements of lung function and capacity, and physical and laboratory measures.

 

Eligible Sample

Survey participants, ages 6 to 79 years, were eligible for FENO testing. Examinees that had current chest pain or a physical problem with forceful expiration, or those who were using supplemental oxygen were medically-excluded from participating.

 

Protocol and Procedure

FENO was measured using the Aerocrine NIOX MINO®, a portable, hand-held NO analyzer (Aerocrine AB, Solna, Sweden) approved by the FDA in 2008. This device relies on an electrochemical sensor to detect exhaled NO levels and provides measurements of from 5 to 300 ppb in whole numbers. The testing was conducted with participants sitting in front of a mirror so they could see display prompts on the NO analyzer screen. Holding the device, participants were asked to first empty their lungs, then to place their mouth on the disposable analyzer's filter mouthpiece and to fill their lungs to capacity with NO-free air. Participants are then asked to blow out all of their air at a constant pressure while exhaled NO from the bronchial tree is measured. The NIOX MINO® has a dynamic flow restrictor to stabilize flow rate at 50 ml/sec. The device automatically provides auditory and visual cues to assist in performing the test correctly. The health technicians also coach participants to maintain the air flow at a slow, fixed, steady rate. The standard exhalation time, as specified by the manufacturer, was 10 seconds for examinees who were at or above 130 cm in height, and 6 seconds for those below 130 cm. The Respiratory Health ENO Procedures Manual provides detailed description of the examination procedure. The manual is available at : http://www.cdc.gov/nchs/nhanes/nhanes2007-2008/current_nhanes_07_08.htm

The test result, an integer between 5-300 ppb, is displayed on the screen of the device 140 seconds after a valid test is completed. Codes indicating a result either above or below the range of the device detection limit, as well as error codes are also displayed on the screen. It is common for current smokers to have repeat FENO levels below the limit of detection. Results indicating a value above the limit of detection are unusual, and subsequent measurements are most often within the normal range of the test device.

The NHANES protocol required two valid FENO measurements that were reproducible, in accordance with testing procedures recommended by the manufacturer and similar to those published by the American Thoracic Society and European Respiratory Society. If either or both of the first two valid FENO measurements was below 30 ppb and the measurements were within 2 ppb of each other, or if both measurements were over 30 ppb and within 10% of each other, then the test was considered reproducible and complete. Two values below the limit of detection were also considered reproducible. If the reproducibility criteria were not met within the first two exhalations, a participant had 2 additional exhalations to satisfy the criteria (up to a total of 4 trials). The examinee's exhalations for which the NIOX MINO® did not display a valid reading, i.e. exhalations that were either too strong or too weak, or any other reasons for failing to achieve a successful exhalation were recorded as attempts. Examinees were not always able to meet the criteria for a reproducible measurement even within the ten attempts allowed to perform the exhalation, as indicated by the exam status variable ENXSTAT.

 

Quality Assurance & Quality Control

The Chief Health Technician, at each MEC, monitored ongoing staff performance in the field. Health technician performance was also monitored using direct observation during periodic site visits. The NIOX MINO® monitor was cleaned and calibrated in accordance with the requirements via regularly scheduled quality control checks by the Health Technicians and verified by supervisory staff. Ambient air testing was conducted daily, and temperature and humidity collection in the respiratory health room was ongoing. A QC sensor verification was conducted at FENO levels of 15 and 75 ppb and and a QC filter checks were also conducted to check a “blank sample” at 0 ppb. Each pre-calibrated NIOX MINO® sensor has a maximum of 300 measurements and sensors were replaced in the device when 30 measurements remained. Generally, 2-3 sensors were used at each NHANES MEC location. The sensor shelf life is 1 year from the date of manufacture, and the device shelf life is 3.5 years from the date of manufacture, or up to 1500 uses. The Respiratory Health ENO Procedures Manual provides detailed descriptions of the quality assurance and quality control measures that were used over the course of the 2007-8 data collection period.

Periodically, batches of used sensors were returned to the manufacturer (Aerocrine) to determine if they still met the test specification quality control criteria. Results from these checks were provided to NCHS. A linear regression model based on the age of the sensor at the time of re-testing and the age of sensor at use was provided by the manufacturer to adjust any drift from the initial calibration specifications of 15% or greater at 200 ppb. The model for the adjustment assumes a linear drift over the lifetime of the sensor. In the NHANES 2007-8 data, less than 5% of the examinees had measurements that were adjusted. The median adjustment was 9% lower than the original measurement at the time of collection.

Data Processing and Editing

Data were reviewed and edited as necessary to ensure internal data consistency.

 

Analytic Notes

Screening Questions ENX040 –ENX100: A series of questions that vary by age were administered in the examination to support data analysis and interpretation. Examinees 12 and older were asked the questions while waiting for the test results after the first acceptable exhalation. Parents of youth 6-11 years were asked these questions, as well as the two medical exclusion questions (ENQ010 and ENQ020) prior to the exam.

Exhaled NO Status Code (ENXSTAT): This single variable provides a completion code for the component:

1: Two measurements met the reproducibility criteria (as described in the Protocol/Procedures section of this document). Only examinees with this status code have a calculated mean FENO value (ENXMEAN).
2: At least one acceptable measurement was obtained. For those with two or more measurements, results were not reproducible.
3: Unable to perform test. Attempted the exhalation up to 10 times but were not successful in achieving a measurement.
4: Medically excluded. Responded positively to or did not answer one of two exclusion questions (ENQ010, ENQ020) prior to the test.
5: Test was not conducted for reason described in ENXCMT.

ENXTR1G, ENXTR2G, ENXTR3G, ENXTR4G: These variables indicate a trial status, respectively, for each of the valid FENO readings that were obtained; i.e., whether an exhalation produced a measurement that was within range of the acceptable device specifications (5-300 ppb), or whether it was either above or below the instrument's limit of detection. If all attempts were used (up to 10 total, across all trials) or the examinee wished to terminate the exam, then a “could not obtain result ” response was recorded.

ENXTR1Q, ENXTR2Q, ENXTR3Q, ENXTR4Q: These variables indicate the numeric value for the FENO reading if it fell within the NIOX MINO® measurement range (5-300 ppb). If the trial status indicates that the measurement was not within the range or could not be obtained, then the FENO measurement will be missing.

ENXMEAN: For analytic purposes,this variable was created for the average of two reproducible measurements. Results from up to 4 successful exhalation trials (ENXTR1Q, ENXTR2Q, ENXTR3Q, ENXTR4Q) were used to assess reproducibility, and the two reproducible FENO measurements were averaged to create a mean value (ENXMEAN). Two measurements below the limit of detection of the device (i.e., less than 5 ppb) were also considered reproducible and given a “fill” value of 3.5 ppb. This value was determined using the same calculation applied to the NHANES laboratory data - the limit of detection divided by the square root of two. Analysts may choose to use an alternate value for FENO levels below the limit of detections, or to exclude records with these values from their analyses.

Sample Weights: The NHANES full sample 2-Year MEC Exam Weights (WTMEC2YR) should be used to analyze the 2007-8 FENO data. Please refer to the NHANES Analytic Guidelines (http://www.cdc.gov/nchs/nhanes/nhanes2003-2004/analytical_guidelines.htm) and the on-line NHANES Tutorial (http://www.cdc.gov/nchs/tutorials) for further details on the use of sample weights and other analytic issues.

Additional 2007-8 NHANES Data on Respiratory Health:
The NHANES 2007-8 Respiratory Health Component also included Spirometry (SPX_E) and Household Interview Questionaire data on a prior diagnosis of asthma and COPD (MCQ_E), recent respiratory symptoms such as cough and wheezing (RDQ_E), and data for the participant's current prescription medications (RXQ_RX_E; RXQ_DRUG). In addition raw data for the spirometry curves attempted by each participant is released in a separate dataset (SPXRAW_E). The raw data permits users to graph a participant's spirometry test curves. It is also intended for the use of data analysts who may want to perform more advanced modeling studies with the raw data.

 

References

Codebook and Frequencies

SEQN - Respondent sequence number

Variable Name:
SEQN
SAS Label:
Respondent sequence number
English Text:
Respondent sequence number
Target:
Both males and females 6 YEARS - 79 YEARS

ENXSTAT - Status code for ENO exam

Variable Name:
ENXSTAT
SAS Label:
Status code for ENO exam
English Text:
Status code for ENO exam
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Two reproducible FENO measurements 6188 6188
2 One or more FENO measurement; not reproducible 182 6370
3 Attempted exam; no FENO measurements 391 6761
4 Medical exclusion; no FENO measurements 196 6957
5 Exam not done; no FENO measurements 786 7743 ENXCMT
. Missing 0 7743

ENXCMT - Comment for ENO exams not done

Variable Name:
ENXCMT
SAS Label:
Comment for ENO exams not done
English Text:
Comment for ENO exams not done
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Safety exclusion 8 8
2 SP refusal 48 56
3 No time 26 82
4 Physical limitation 32 114
5 Communication problem 31 145
6 Equipment failure 21 166
7 SP ill/emergency 13 179
14 Interrupted 1 180
27 Proxy no information 3 183
56 Came late/left early 526 709
84 SP with child 43 752
99 Other 34 786
. Missing 6957 7743

ENQ010 - Breathing problem require oxygen?

Variable Name:
ENQ010
SAS Label:
Breathing problem require oxygen?
English Text:
Medical Exclusion Question
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 67 67 End of Section
2 No 6887 6954
7 Refused 0 6954 End of Section
9 Don't know 3 6957 End of Section
. Missing 786 7743

ENQ020 - Problem taking deep breath?

Variable Name:
ENQ020
SAS Label:
Problem taking deep breath?
English Text:
Medical Exclusion Question
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 121 121 End of Section
2 No 6761 6882
7 Refused 0 6882 End of Section
9 Don't know 5 6887 End of Section
. Missing 856 7743

ENQ040 - Smoked last hour?

Variable Name:
ENQ040
SAS Label:
Smoked last hour?
English Text:
Within the last hour have you smoked a cigarette, cigar, pipe , or used any other tobacco product?
Target:
Both males and females 16 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 368 368
2 No 4536 4904
7 Refused 0 4904
9 Don't know 0 4904
. Missing 2839 7743

ENQ050 - Exercised strenuously last hour?

Variable Name:
ENQ050
SAS Label:
Exercised strenuously last hour?
English Text:
[Within the last hour] have you exercised strenuously?
Target:
Both males and females 12 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 73 73
2 No 5366 5439
7 Refused 0 5439
9 Don't know 0 5439
. Missing 2304 7743

ENQ060 - Ate or drink last hour?

Variable Name:
ENQ060
SAS Label:
Ate or drink last hour?
English Text:
[Within the last hour] have you had anything to eat or drink?
Target:
Both males and females 12 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 3444 3444
2 No 1994 5438
7 Refused 0 5438
9 Don't know 1 5439
. Missing 2304 7743

ENQ070 - Ate NO-rich vegetables, 3 hours?

Variable Name:
ENQ070
SAS Label:
Ate NO-rich vegetables, 3 hours?
English Text:
Within the last three hours have you eaten beets, broccoli, cabbage, celery, lettuce, spinach or radishes?
Target:
Both males and females 12 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 214 214
2 No 5224 5438
7 Refused 0 5438
9 Don't know 1 5439
. Missing 2304 7743

ENQ080 - Ate NO-rich rich meats, 3 hours?

Variable Name:
ENQ080
SAS Label:
Ate NO-rich rich meats, 3 hours?
English Text:
Within the last three hours have you eaten bacon, ham, hot dogs or smoked fish?
Target:
Both males and females 12 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 207 207
2 No 5232 5439
7 Refused 0 5439
9 Don't know 0 5439
. Missing 2304 7743

ENQ090 - Used oral or inhaled steroids, 2 days?

Variable Name:
ENQ090
SAS Label:
Used oral or inhaled steroids, 2 days?
English Text:
Within the last two days {have you/has SP} used any oral or inhaled steroids? This list provides some examples
English Instructions:
SHOW HANDCARD
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 248 248
2 No 6118 6366
7 Refused 0 6366
9 Don't know 4 6370
. Missing 1373 7743

ENQ100 - Cough, cold, resp illness, 7 days?

Variable Name:
ENQ100
SAS Label:
Cough, cold, resp illness, 7 days?
English Text:
In the past 7 days, {have you/has SP} had a cough, cold, phlegm, runny nose or other respiratory illness? Do not count allergies or hay fever
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Yes 1354 1354
2 No 5013 6367
7 Refused 0 6367
9 Don't know 3 6370
. Missing 1373 7743

ENAATMPT - Total number of exhalation attempts

Variable Name:
ENAATMPT
SAS Label:
Total number of exhalation attempts
English Text:
Enter total number of attempts
English Instructions:
ENTER TOTAL NUMBER OF ENO ATTEMPTS
Target:
Both males and females 6 YEARS - 79 YEARS
Hard Edits:
1 to 10
Code or Value Value Description Count Cumulative Skip to Item
1 to 10 Range of Values 6761 6761
. Missing 982 7743

ENXTR1G - Trial 1 result status

Variable Name:
ENXTR1G
SAS Label:
Trial 1 result status
English Text:
Trial 1: Status of Exhalation Attempt
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Acceptable measurement 5585 5585
2 Could Not Obtain 391 5976
3 < 5 ppb 785 6761
4 > 300 ppb 0 6761
. Missing 982 7743

ENXTR1Q - Trial 1 FENO Measurement (ppb)

Variable Name:
ENXTR1Q
SAS Label:
Trial 1 FENO Measurement (ppb)
English Text:
Trial 1 measurement of fractional concentration of orally exhaled nitric oxide (FENO) in parts per billion
Target:
Both males and females 6 YEARS - 79 YEARS
Hard Edits:
5 to 300
Code or Value Value Description Count Cumulative Skip to Item
5 to 218 Range of Values 5585 5585
. Missing 2158 7743

ENXTR2G - Trial 2 result status

Variable Name:
ENXTR2G
SAS Label:
Trial 2 result status
English Text:
Trial 2: Status of Exhalation Attempt
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Acceptable measurement 5744 5744
2 Could Not Obtain 88 5832
3 < 5 ppb 530 6362
4 > 300 ppb 4 6366
. Missing 1377 7743

ENXTR2Q - Trial 2 FENO Measurement (ppb)

Variable Name:
ENXTR2Q
SAS Label:
Trial 2 FENO Measurement (ppb)
English Text:
Trial 2 measurement of fractional concentration of orally exhaled nitric oxide (FENO) in parts per billion
Target:
Both males and females 6 YEARS - 79 YEARS
Hard Edits:
5 to 300
Code or Value Value Description Count Cumulative Skip to Item
5 to 227 Range of Values 5744 5744
. Missing 1999 7743

ENXTR3G - Trial 3 result status

Variable Name:
ENXTR3G
SAS Label:
Trial 3 result status
English Text:
Trial 3: Status of Exhalation Attempt
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Acceptable measurement 1891 1891
2 Could Not Obtain 49 1940
3 < 5 ppb 119 2059
4 > 300 ppb 1 2060
. Missing 5683 7743

ENXTR3Q - Trial 3 FENO Measurement (ppb)

Variable Name:
ENXTR3Q
SAS Label:
Trial 3 FENO Measurement (ppb)
English Text:
Trial 3 measurement of fractional concentration of orally exhaled nitric oxide (FENO) in parts per billion
Target:
Both males and females 6 YEARS - 79 YEARS
Hard Edits:
5 to 300
Code or Value Value Description Count Cumulative Skip to Item
5 to 215 Range of Values 1891 1891
. Missing 5852 7743

ENXTR4G - Trial 4 result status

Variable Name:
ENXTR4G
SAS Label:
Trial 4 result status
English Text:
Trial 4: Status of Exhalation Attempt
Target:
Both males and females 6 YEARS - 79 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Acceptable measurement 227 227
2 Could Not Obtain 11 238
3 < 5 ppb 4 242
4 > 300 ppb 0 242
. Missing 7501 7743

ENXTR4Q - Trial 4 FENO Measurement (ppb)

Variable Name:
ENXTR4Q
SAS Label:
Trial 4 FENO Measurement (ppb)
English Text:
Trial 4 measurement of fractional concentration of orally exhaled nitric oxide (FENO) in parts per billion
Target:
Both males and females 6 YEARS - 79 YEARS
Hard Edits:
5 to 300
Code or Value Value Description Count Cumulative Skip to Item
5 to 171 Range of Values 227 227
. Missing 7516 7743

ENXMEAN - Mean, 2 reproducible FENO measures (ppb)

Variable Name:
ENXMEAN
SAS Label:
Mean, 2 reproducible FENO measures (ppb)
English Text:
Mean of two reproducible FENO measurements, in parts per billion
Target:
Both males and females 6 YEARS - 79 YEARS
Hard Edits:
3.5 to 301
Code or Value Value Description Count Cumulative Skip to Item
3.5 to 217.5 Range of Values 6188 6188
. Missing 1555 7743