NHANES III Serum Latex Allergy (IgE) Data Analysis Issues
The analysis of the latex antibody data from NHANES III (1988-94) samples will not be completed due to data quality issues associated with data generated from the second half of the survey and method changes from the laboratory method used in the first half of the study.
In 1994, the Centers for Disease Control and Prevention (CDC) tested stored sera from phase 1 of the National Health and Nutrition Examination Survey (NHANES III 1988-91) from participants age 17-60 years to estimate the prevalence of latex specific IgE antibody in this representative sample of the U.S. population. The AlaStat assay was chosen for the study after being compared with three other latex immunoassays in a blinded comparison involving clinically-defined specimens; the results of this comparative study have been published in a peer-reviewed journal. Also, at the time of the study, this assay was the only FDA-approved method for detection of latex-specific IgE in sera. Absorbance readings were measured using a spectrophotometer. Testing was performed at the National Center for Infectious Diseases at CDC. To ensure competency in conducting the test, CDC personnel received on-site training by the manufacturer before testing began. As part of quality control measures, all specimens (N=5,500) tested by CDC were tested in duplicate and in some instances in triplicate runs.
From 1996-98, investigators at the Food and Drug Administration (FDA) tested stored sera from phase 2 NHANES III (1991-94) participants for latex antibody to further assess the prevalence of latex specific IgE antibody in the population. They requested and tested samples from all individuals age 6-19 years, those who were allergy skin-tested age 20-59 years, and all individuals age 60 and over. They also retested samples from phase 1 of the survey. The testing was performed at the FDA laboratory in Dallas, Texas. The test used was a newer AlaStat assay. It was assumed that the two assays were comparable since both were from the same manufacturer and used allergens in a liquid format with the newer assay using a microplate format. This assay is the currently marketed assay and is being used to test samples from the current NHANES survey.
Before CDC could release its analysis of phase 1 data, data became available to CDC from the FDA laboratory in fall 1998. Preliminary analysis of data from phase 1 and phase 2 of the survey yielded very different results. Among the phase 1 specimens retested in the FDA laboratory in 1998, only 50% had results similar to their phase 1 readings done at the CDC laboratory. Preparation of an analytic report to discuss these differences and completion of analyses on seroprevalence and risk factors for the presence of latex specific IgE antibody were being finalized early in 1999. At this time, the FDA laboratory informed CDC and FDA epidemiologists that there were quality control problems with some of the laboratory runs along with the possibility of errors in data transmittal. This called into question the quality of the phase 2 results. It also made definitive comparisons with phase 1 data more difficult.
An extensive internal review of the phase 2 results was begun by FDA in response to continuing questions raised, in the middle to latter part of 1999, about the validity and viability of the data. The review was completed in June 2000. Based upon this review, the FDA has concluded that the data cannot be used for scientific purposes. Numerous potential errors and faults were uncovered that indicated potential problems with instrument calibration and real-time data production review. It is not possible to separate the valid data from questionable data in any meaningful manner.
The current NHANES test for latex specific IgE antibody in the current NHANES (NHANES '99+) is being performed by CDC using the same AlaStat Microplate method that was used on the phase 2 specimens. Because there is no gold standard for latex IgE serologic tests and population screening in a general sample such as NHANES is known to produce more variable results than screening in high prevalence populations, CDC has instituted a rigid testing protocol. All samples are done in duplicate with concordant results reported. Data from the first 3 years of the present NHANES (1999-2001) should be available in a fully documented public release data set in 2002. Because the AlaStat assay has changed to an automated microplate method from the older manual tube method that was used to produce the latex allergy data from the first phase of NHANES III, analyses of these data should take this into account when comparing with results from other, more recent studies.