National Health and Nutrition Examination Survey

The estimated prevalence of human immunodeficiency virus (HIV) infection in the United States population is an important measure of the extent of the medical and financial burden the nation faces due to this virus. The current NHANES (1999-present) and HIV antibody data from NHANES III (1988–94) serves as a baseline for monitoring the changes in the epidemic over time in the general population of the United States.

Examined participants aged 18–59 years were eligible.

 HIV antibody blood assay test results:

All specimens were tested using the Synthetic Peptide Enzyme Immunoassay (EIA) (Genetic Systems HIV-1/HIV-2 Peptide EIA) for the detection of antibody to human immunodeficiency virus type 1 or type 2 (HIV-1 or HIV-2) or both (Bio-Rad Laboratories, Redmond, WA). Any specimen that reacted in an initial test was retested in duplicate with the Genetic Systems HIV-1/HIV-2 Peptide EIA. Initially, reactive specimens that were reactive in either one or both duplicates from the repeat testing are referred to as “repeatedly reactive.” These repeatedly reactive specimens were then tested with a more specific test, the Cambridge Biotech HIV-1 Western Blot Kit (Calypte Biomedical Corporation, Rockville, MD).

The combination of electrophoretic separation of complex mixtures of antigens with the highly sensitive immunoblotting technique has been useful in characterizing the antigenic profile of HIV-1 and describing the immune response to this virus in exposed or infected persons.

The Cambridge Biotech HIV-1 Western Blot Kit, when used as directed, will detect antibodies to HIV-1 when present in human serum or plasma. The position of bands on the nitrocellulose strips allows this antibody reactivity to be associated with specific viral antigens.

The Cambridge Biotech HIV-1 Western Blot Kit is manufactured by Calypte Corporation from HIV-I propagated in an H9/HTLV-IIIb T lymphocyte cell line. The partially purified virus is inactivated by treatment with psoralen, ultraviolet light, and detergent disruption. Specific HIV-1 proteins are fractionated according to molecular weight by electrophoresis on a polyacrylamide slab gel in the presence of sodium dodecyl sulfate (SDS).

The separated HIV-1 proteins are elecrotransferred from gel to a nitrocellulose membrane, which is then washed, blocked (to minimize nonspecific immunoglobulin binding), and packaged. Individual nitrocellulose strips are incubated with serum or plasma specimens, or controls. During incubation, if HIV-1 antibodies are present in the specimen, they will bind to the viral antigens bound to the nitrocellulose strips. The strips are washed again to remove unbound material.

Visualization of the human immunoglobulins specifically bound to HIV-1 proteins is accomplished in situ by using a series of reactions with goat anti-human IgG conjugated with biotin, avidin conjugated with horseradish peroxidase (HRP), and the HRP substrate 4-chloro-1-naphthol. If antibodies to any of the major HIV-1 antigens are present in the specimen in sufficient concentration, bands corresponding to the position of one or more of the following HIV-1 proteins (p) or glycoproteins (gp) will be seen on the nitrocellulose strip: p17, p24, p31, gp41, p51, p66, gp120, gp160 (number refers to apparent molecular mass in kilodaltons).

Refer to the Laboratory Method Files section for detailed laboratory procedure manual(s) of the methods used.

There were no changes to the lab method, lab equipment, or lab site for this component in the NHANES 2013-2014 cycle.

HIV Antibody / HIV Western Blot Confirmatory Test (October 2015)

Serum specimens were processed, stored, and shipped to the Division of AIDS, STD, and TB, National Center for HIV, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, GA for analysis.

Detailed instructions on specimen collection and processing are discussed in the NHANES Laboratory Procedures Manual (LPM). Vials are stored under appropriate frozen (–30°C) conditions until they are shipped to the Division of AIDS, STD, and TB, National Center for HIV, STD, and TB Prevention for testing.

The NHANES quality assurance and quality control (QA/QC) protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed QA/QC instructions are discussed in the NHANES LPM.

Mobile Examination Centers (MECs)

Laboratory team performance is monitored using several techniques. NCHS and contract consultants use a structured quality assurance evaluation during unscheduled visits to evaluate both the quality of the laboratory work and the quality-control procedures. Each laboratory staff member is observed for equipment operation, specimen collection and preparation; testing procedures and constructive feedback are given to each staff member. Formal retraining sessions are conducted annually to ensure that required skill levels were maintained.

Analytical Laboratories

NHANES uses several methods to monitor the quality of the analyses performed by the contract laboratories. In the MEC, these methods include performing blind split samples collected on “dry run” sessions. In addition, contract laboratories randomly perform repeat testing on 2% of all specimens.

Progress reports containing any problems encountered during shipping or receipt of specimens, summary statistics for each control pool, QC graphs, instrument calibration, reagents, and any special considerations are submitted to NCHS quarterly. The reports are reviewed for trends or shifts in the data. The laboratories are required to explain any identified areas of concern.

All QC procedures recommended by the manufacturers were followed. Reported results for all assays meet the Division of AIDS, STD, and TB, National Center for HIV, STD, and TB Prevention’ quality control and quality assurance performance criteria for accuracy and precision.

The data were reviewed. Incomplete data or improbable values were sent to the performing laboratory for confirmation.

Refer to the 2013 - 2014 Laboratory Data Overview for general information on NHANES laboratory data.

Demographic and Other Related Variables

The analysis of NHANES laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2013-2014 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample design variables. The recommended procedure for variance estimation requires use of stratum and PSU variables (SDMVSTRA and SDMVPSU, respectively) in the demographic data file.

The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture.

This laboratory data file can be linked to the other NHANES data files using the unique survey participant identifier (i.e., SEQN).

The serum specimens were first tested by enzyme immunoassay (EIA) and confirmed by Western blot (WB). If the EIA was repeatedly negative, the HIV antibody result was coded as negative. If the EIA was positive and the WB was positive, the result was coded as positive. If the EIA was positive or indeterminate but the WB was negative, the result was coded as negative. If the EIA was positive or indeterminate but the WB was indeterminate, the result was coded as indeterminate.

Detection Limits

Since this data is reported as qualitative data the use of lower LLODs isn’t applicable.

Exam sample weights should be used for analyses. Please refer to the NHANES Analytic Guidelines and the on-line NHANES Tutorial for further details on the use of sample weights and other analytic issues.