Retesting Of Samples Research Articles

Impact of a Chemistry-Based DNA Extraction Method on Performance of a Commercial Amplification Assay for Detection of Mycobacterium tuberculosis Complex

Impact of a Chemistry-Based DNA Extraction Method on Performance of a Commercial Amplification Assay for Detection of <i>Mycobacterium tuberculosis</i> Complex

Evaluation and Implementation of Rapid HIV Tests: The Experience in 11 African Countries

Rapid HIV testing enables HIV prevention and care services to expand to settings with limited laboratory infrastructure. The World Health Organization recommends that prior to their implementation, rapid HIV tests first be evaluated at a reference laboratory and then at points-of-service, and that measures to ensure quality of testing be in place. We describe the experience of 11 African countries that implemented rapid HIV testing using this process. A questionnaire regarding rapid test evaluations and quality assurance measures was administered to personnel in ministries of health, reference laboratories, and Centers for Disease Control and Prevention programs in 11 African countries. In reference laboratory evaluations, median sensitivity was above 99% for 10 of 15 rapid tests and median specificity was above 99% for 13 of 15 rapid tests. Similar results were observed in evaluations at point-of-service sites. Rapid testing algorithms have been implemented in over 600 sites in nine of the countries. Concordance between point-of-service rapid testing and reference laboratory retesting of samples ranged from 95.7% to 99.5% (median: 98.7%). A systematic approach to the evaluation and implementation of rapid HIV tests was useful in ensuring accurate, decentralized testing even when conducted by persons with limited laboratory experience.

Resolving repeatedly borderline results of Hybrid Capture 2 HPV DNA Test using polymerase chain reaction and genotyping

The Hybrid Capture 2 HPV DNA Test (hc2) (Digene Corporation, Gaithersburg, MD) is at present the only FDA approved assay for routine detection of human papillomavirus (HPV) infections. A significant analytical inaccuracy of the hc2 near to cut-off was reported recently. To address this problem, 240 samples with repeatedly borderline/equivocal/indeterminate hc2 results (samples with repeated RLU/CO values between 0.4 and 4.0) were tested using the PGMY09/PGMY11 consensus PCR and genotyping in order to resolve their high-risk HPV status. All PGMY09/PGMY11 PCR negative samples were tested in addition using CPI/IIg consensus PCR. A false negative rate of 11.3% and false positive rate of 19.1% were recorded in the samples with repeatedly borderline hc2 results. The corresponding hc2 false reactivity rates in 95 samples selected at random which were clearly hc2 negative (samples with RLU/CO values less than 0.4) and 124 samples selected at random which were clearly hc2 positive (samples with RLU/CO values more than 4.0) were 4.2% and 5.6%, respectively. The proportion of hc2 false reactivity increased with proximity to the hc2 cut-off value. According to the results of the present study, the introduction of an hc2 grey-zone and retesting of samples with repeatedly borderline hc2 results by an alternate HPV detection method, such as the PGMY09/PGMY11 consensus PCR and genotyping, is recommended.

Prediction of autoantibody positivity and progression to type 1 diabetes: Diabetes Autoimmunity Study in the Young (DAISY).

Diabetes Autoimmunity Study in the Young (DAISY) has followed 1972 children for islet autoimmunity and diabetes: 837 first-degree relatives of persons with type 1 diabetes and 1135 general population newborns identified through human leukocyte antigen (HLA) screening. During follow-up of 4.06 yr (range, 0.17-9 yr), serial determination of autoantibodies to glutamic acid decarboxylase, protein tyrosine phosphatase IA2, and insulin has generated approximately 20,000 results. Among 162 children with at least one positive autoantibody, in 31% the test was false positive (autoantibodies were negative twice on blinded duplicate aliquots), in 31% it was transiently positive (confirmed on blinded duplicate aliquots but negative on follow-up), and in 36% it was persistently positive. Using proportional hazards modeling, the HLA-DR3/4 DQ8 genotype, another positive autoantibody at the first positive visit, and level of autoantibody were predictive of persistent positivity. Only HLA-DR3/4 DQ8 genotype was predictive of progression to diabetes in proportional hazards modeling. This prospective study reveals that cross-sectional determination of islet autoantibodies in a population with relatively low previous probability of autoimmunity identifies as "positive" a large number of individuals who are either false or transiently positive. Predictive value of autoantibodies increases with blinded duplicate and independent sample retesting and incorporation of the level of autoantibody in the predictive algorithm.