Table of Contents

Locator Record

Title: Hepatic/Gallbladder Ultrasound and Hepatic Steatosis - Second Exam (HGUHSSE )
Contact Number: 1-866-441-NCHS
Years of Content: 1988 - 1994
First Published: January, 2011
Revised: NA
Access Constraints: None
Use Constraints: None
Geographic Coverage: National
Subject:Hepatic Gallbladder Ultrasound, Hepatic Steatosis, Fatty Liver
Record Source: NHANES 1988 - 1994
Survey Methodology: NHANES 1988 - 1994 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

Between 2009 - 2010, the hepatic steatosis (fatty liver) was assessed by re-reviewing the archived gall bladder ultrasound video images originally obtained in NHANES III between 1988 and 1994. The examination made it possible to grade the presence of fat within the hepatic parenchyma. The NHANES III Second Exam Sample was a sub-study of NHANES III, conducted for research purposes. These research files are intended to provide additional data for use with special statistical methods to improve estimates from the main survey data and for methodologic investigations. Be sure to read the documentation of the primary exam carefully before attempting any analysis.

 

Eligible Sample

No statistical sampling design was applied for the second exam. However, a nonrandom sample of about five percent was obtained by selecting approximately 20 participants from the roughly 400 sample persons examined at each survey location. The following general guidelines were used by the NHANES-Mobile examination center staff to select participants for the second exam: 1) select mainly adults, 2) half between the ages of 20-39 years, and half over 40 years; 3) select about half men and half women. The Hepatic/Gallbladder Ultrasound Examination Second/Replicate Examination sample consists of 1,121 adults 20-74 years of age, with ultrasounds performed on two separate occasions. Fasting was preferred but not required.

 

Protocol and Procedure

The second exams were scheduled after the first or primary exams, when possible at the same time of day as the first exam. The second exams were conducted over the same time period as the primary exams for a particular survey location by the same MEC staff, although priority was given to scheduling and completing primary exams. The second exams were administered following the same protocols as for the primary exam.

Ultrasound examinations were originally recorded using a Toshiba Sonolayer SSA-90A and Toshiba video recorder. The examinations were performed using standardized procedures (Gallbladder Ultrasonography Procedure Manual, Third National Health and Examination Survey, http://www.cdc.gov/nchs/data/nhanes/nhanes3/cdrom/nchs/manuals/gallblad.pdf), which had been developed to ensure that each examination was performed in a consistent manner and that the results of each examination were accurate and reliable.

For the hepatic steatosis assessments, the video tapes of the NHANES III ultrasound examinations were digitized using a DVD-VHS Video cassette Recorder (SONY RDR-VX560) onto a Recordable DVD (Memorex, +R or +RW). DVD video-images were reviewed using a Dell Flat Panel Monitor (2408WFP, active matrix, thin-film transistor, liquid crystal display, 24-inch (609.6 mm) viewable area display, 1920 x 1200 resolution).

Three ultrasound readers were trained and approved by a board certified radiologist who is specialized in hepatic imaging.

All ultrasound assessments for hepatic steatosis were conduct by readers who had no access to any other participant data and who were not aware if the study was a second exam, nor were aware of the results of the first exam.

For practical reasons, NHANES III Phase 2 ultrasounds were reviewed before Phase 1.

For more detailed information regarding the training and data collection data users are encouraged to review the Hepatic Steatosis Procedures Manual, NCHS 2010. http://www.cdc.gov/nchs/data/nhanes/nhanes3/Hepatic_Steatosis_Ultrasound_Procedures_Manual.pdf

 

Quality Assurance & Quality Control

A radiologist, with 21 years of experience in the interpretation of ultrasound images, trained, observed, and approved the readers. Routine monitoring of the reliability (both inter- and intra-reader) was conducted every three months, throughout the study to detect if there was any need for re-training.

A more detailed description of the Training, Quality Assurance and Quality Control is included in the Procedure Manual, Hepatic Steatosis, NCHS, 2010. http://www.cdc.gov/nchs/data/nhanes/nhanes3/Hepatic_Steatosis_Ultrasound_Procedures_Manual.pdf

 

Data Processing and Editing

The primary finding variable (GURHSPF), is a 4 level variable. A primary finding recode (GURHSPFR) variable was created from this variable. This is a two category variable: hepatic steatosis yes or no. The recode value of "Yes" indicates that moderate or severe hepatic steatosis was present. A recode value of "No" indicates that the liver was normal or had mild hepatic steatosis.

 

Analytic Notes

Due to the research nature of these data, special caution should be used in
analysis. All analyses should include thorough investigation of the potential selection bias of this small non-random sub-sample. Careful attention to identifying and evaluating differences in important characteristics (e.g., age and race-ethnicity) between the subsample and the main sample should be considered along with other issues.

The second exam data can be linked to the primary exam data and the household interview data using the unique identifier (SEQN). This is necessary to obtain the demographic data for the sample. NCHS recommends that the survey design variables (e.g., sample weights) not be linked with the second exam data, since the survey design variables were created for the full sample. There are no sample weights or other design variables specifically created for the second exam sample.

Because the second exams were identical to the primary exams, the file structure for the second exams is the same as for the primary exam files. The variable nomenclature is the same with the following important distinction: "R" was added to the primary exam variables names in the third positition.

Users are encouraged to use the primary finding recode (GURHSPFR) variable for all the analyses. This recode will help to avoid potential overlap between mild and moderate hepatic steatosis. The data file provides all the different parameters that were obtained for the assessment of hepatic steatosis: liver to kidney contrast, parenchymal brightness, deep beam attenuation, vessel walls definition, and gallbladder wall definition and the overall confidence in the assessment. These parameters should allow more experienced users to explore alternative criteria and to conduct sensitivity analyses.

GURHSQC (Hepatic Steatosis assessment status comment) is a quality control variable that allowed NCHS to monitor the status of the assessment and the reasons readers provided why an exam was not analyzed or missing. The variable is provided in the data release file to allow analysts to have some information on missing data. Image is present, but ungradable may indicate any of the following: VHS tape was damaged, the ultrasound has a very poor quality that impairs the assessment of hepatic steatosis (e.g. presence of gas, patient examined in a wheelchair). No image reflects the fact that there was no ultrasound available for the participant.

In addition, for each of the above mentioned parameters (liver to kidney contrast, parenchymal brightness, deep beam attenuation, vessel walls definition, and gallbladder wall definition), in cases where the ultrasound technique and coverage did not include the parameter, then we marked "cannot assess" (coded as 9).

 

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 20 YEARS - 74 YEARS

GURHSQC - HS Assessment Status

Variable Name:
GURHSQC
SAS Label:
HS Assessment Status
English Text:
HS Assessment Status
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Image is present and gradable 1121 1121
7 Image is present, but ungradable 13 1134
8 No image 822 1956
. Missing 0 1956

GURHSLKC - Liver to kidney contrast

Variable Name:
GURHSLKC
SAS Label:
Liver to kidney contrast
English Text:
Liver to kidney contrast
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 No 527 527
2 Yes 247 774
7 Image is present, but ungradable 13 787
8 No image 822 1609
9 Cannot assess 347 1956
. Missing 0 1956

GURHSPB - Parenchymal brightness

Variable Name:
GURHSPB
SAS Label:
Parenchymal brightness
English Text:
Parenchymal brightness
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Normal 656 656
2 Mild 71 727
3 Moderate 247 974
4 Severe 147 1121
7 Image is present, but ungradable 13 1134
8 No image 822 1956
9 Cannot assess 0 1956
. Missing 0 1956

GURHSDBA - Deep beam attenuation

Variable Name:
GURHSDBA
SAS Label:
Deep beam attenuation
English Text:
Deep beam attenuation
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Normal 838 838
2 Blurred 162 1000
7 Image is present, but ungradable 13 1013
8 No image 822 1835
9 Cannot assess 121 1956
. Missing 0 1956

GURHSVW - Vessel walls

Variable Name:
GURHSVW
SAS Label:
Vessel walls
English Text:
Vessel walls
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Normal 920 920
2 Absent 198 1118
7 Image is present, but ungradable 13 1131
8 No image 822 1953
9 Cannot assess 3 1956
. Missing 0 1956

GURHSDGB - Gallbladder wall

Variable Name:
GURHSDGB
SAS Label:
Gallbladder wall
English Text:
Definition of gallbladder wall
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Normal 682 682
2 Blurred 294 976
3 Obliterated 46 1022
7 Image is present, but ungradable 13 1035
8 No image 822 1857
9 Cannot assess 99 1956
. Missing 0 1956

GURHSPF - HS primary finding

Variable Name:
GURHSPF
SAS Label:
HS primary finding
English Text:
HS primary finding
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Normal 684 684
2 Mild 163 847
3 Moderate 186 1033
4 Severe 88 1121
7 Image is present, but ungradable 13 1134
8 No image 822 1956
. Missing 0 1956

GURHSPFR - HS primary finding, recode

Variable Name:
GURHSPFR
SAS Label:
HS primary finding, recode
English Text:
HS primary finding, recode
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 Normal-Mild 847 847
2 Moderate-Severe 274 1121
7 Image is present, but ungradable 13 1134
8 No image 822 1956
. Missing 0 1956

GURCHSC - Confidence in HS assessment

Variable Name:
GURCHSC
SAS Label:
Confidence in HS assessment
English Text:
Confidence in HS assessment
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 None 6 6
2 Doubtful 84 90
3 Confident 649 739
4 Absolute 382 1121
7 Image is present, but ungradable 13 1134
8 No image 822 1956
. Missing 0 1956

GURHSREV - HS exam reviewer number

Variable Name:
GURHSREV
SAS Label:
HS exam reviewer number
English Text:
HS exam reviewer number
Target:
Both males and females 20 YEARS - 74 YEARS
Code or Value Value Description Count Cumulative Skip to Item
1 1 730 730
2 2 305 1035
3 3 86 1121
7 Image is present, but ungradable 13 1134
8 No image 822 1956
. Missing 0 1956