Tissue transglutaminase assay (IgA-TTG) and the IgA endomyseal antibody assay (IgA EMA) estimates the prevalence of celiac disease in the United States population. Celiac disease is an intolerance to dietary glutens that has protean manifestations. In population surveys in other countries, it is found in about 0.5 to 1 percent of the population. It may well be as common in the United States, but has not been adequately examined. Advances in diagnostic testing now allow accurate disease prevalence estimates using two step serological testing. To provide reliable population estimates, four to six years of data collection are required.
Participants aged 6 years and older were tested.
Serum specimens were processed, stored and shipped to the Mayo Clinic, Rochester, Minnesota. Detailed instructions on specimen collection and processing can be found in the NHANES Laboratory/Medical Technologists Procedures Manual (LPM)
Tissue transglutaminase assay (IgA-TTG)
An Enzyme-Linked Immunosorbant Assay (ELISA) for the semi-quantitative detection of IgA antibodies to tissue transglutaminase (endomysium) in human serum. Microwells are pre-coated with recombinant human tTG antigen. The calibrators, controls and diluted patient samples are added to the wells and autoantibodies recognizing the tTG antigen bind during first incubation. Unbound proteins are removed during washing and purified peroxidase conjugate is added which binds to the captured human autoantibody; excess is washed. TMB substrate is added which gives a blue reaction product, intensity is proportional to the concentration of autoantibody in the sample. Phosphoric acid is added to stop the reaction which gives the yellow color. Plate is read at 450 nm.
Endomyseal antibody assay (IgA EMA)
Endomysial antibodies of the IgA subclass present in the serum bind to the reticulin component of the endomysium of the smooth muscle in monkey esophagus tissue and can be detected by indirect immunofluorescence. Substrate-bound IgA antibody is identified with a fluorescein-conjugated anti-human IgA (Fab2-specific) conjugate. Positive staining is identified as a reticulated lace-like pattern on perimucosal smooth muscle bands. Sera positive for endomysial antibody are titered to end-point dilutions.
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 Laboratory/Medical Technologists Procedures Manual (LPM).
Refer to the 2011-2012 Laboratory Data Overview for general information on NHANES laboratory data.
The analysis of NHANES 2011-2012 laboratory data must be conducted using the appropriate survey design and demographic variables. The NHANES 2011-2012 Demographics File contains demographic data, health indicators, and other related information collected during household interviews as well as the sample weight variables. The Fasting Questionnaire File includes auxiliary information such as fasting status, the time of venipuncture, and the conditions precluding venipuncture. The demographics and fasting questionnaire files may be linked to the laboratory data file using the unique survey participant identifier (i.e., SEQN).
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.
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | Positive | 28 | 28 | |
| 2 | Negative | 6854 | 6882 | |
| 3 | Weakly positive | 21 | 6903 | |
| . | Missing | 918 | 7821 |
| Code or Value | Value Description | Count | Cumulative | Skip to Item |
|---|---|---|---|---|
| 1 | Positive | 25 | 25 | |
| 2 | Negative | 22 | 47 | |
| 3 | Weakly positive | 2 | 49 | |
| . | Missing | 7772 | 7821 |