National Health and Nutrition Examination Survey

Among children ages 6-19 years who participated in NHANES III and had stored serum specimens available, food specific IgE (to cow’s milk, hen’s egg, peanut and shrimp) were measured by ImmunoCAP, a commercially available method of quantifying allergen specific IgE. This panel of food specific IgE was selected to match those measured in NHANES 2005-6, and the analysis method was the same as for NHANES 2005-6.

All children aged 6 to 19 years who participated in NHANES III.

Stored specimens were shipped to Elmhurst Memorial Hospital, Elmhurst, Illinois.  Forty microliters (40 μL) of sample is required for each assay. The ImmunoCAP assay (Thermo Fisher, Kalamazoo, MI) is a sandwich immunoassay. The specific allergen of interest, covalently coupled to the ImmunoCAP™ cellulose carrier (sponge), reacts with the allergen-specific IgE in the participant serum sample. After washing away non-specific IgE, enzyme-labeled antibodies against IgE are added to form a complex. After incubation, unbound anti-IgE is washed away and the remaining bound complex is incubated with a developing agent. After stopping the reaction, the sponge is compressed and the fluorescence of the resulting eluate is measured. The higher the response value, the more allergen-specific IgE is present in the sample. To evaluate the test results, the response for the patient samples is compared directly to the response for the calibrators. Data are reported as concentration of Allergen specific Units (kU/L).

Detailed instructions on specimen collection and processing can be found in the Laboratory Procedures Used for the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994, https://wwwn.cdc.gov/nchs/data/nhanes3/manuals/labman.pdf

The ImmunoCAP measurements were done as recommended by the manufacturer. All QA/QC procedures recommended by the manufacturer were followed.

For samples below the lower limit of detection (LLOD, 0.35kU/L), fill values equal to the LLOD divided by the square root of 2 are used in the public release dataset (0.25). The upper limit of detection (ULOD) was 1000 kU/L. Values above the ULOD were reported as 1001 kU/L.

Two variables are provided for each IgE analyte. The variable name “SS__LC”, with the underscore filled by an allergen-specific code, indicates whether the result was either measurable, below the LLOD or above the ULOD. There are three values: “0”, “1”, and “2”. A “0” value means that the result was measureable. A “1” indicates that the result was below the LLOD. A “2” indicates that the result was above the ULOD.

The other variable type, prefixed “SSX__”, provides the analytic result for that analyte. The variables released are the following :
Sequence number= Sample person identification number
SSF13=Serum IgE antibody to peanut (kU/L)
SSF13LC=Peanut IgE comment code
SSIF1=Serum IgE antibody to egg (kU/L)
SSIF1LC= Egg IgE comment code
SSIF2= Serum IgE antibody to milk (kU/L)
SSIF2LC=Milk IgE comment code
SSF24=Serum IgE antibody to Shrimp (kU/L)
SSF24LC=Shrimp comment code

The analysis of the NHANES III stored samples must be conducted with the key survey design variables and weights incorporated into the analysis. Please refer to the NHANES Analytic Guidelines and the online NHANES Tutorial for further details on the use of sample weights and other analytic issues.