Comparison of the sensitivities and viral load values of the AMPLICOR HIV-1 MONITOR version 1.0 and 1.5 tests.

This study compared the sensitivity and viral load values of the AMPLICOR HIV-1 MONITOR microwell version 1.0, microwell version 1.5, and COBAS version 1.5 tests. Based on the percentage of positive replicates, the microwell version 1.5 and COBAS version 1.5 tests are more sensitive than the microwell version 1.0 test. Viral load values obtained with the COBAS version 1.5 test are lower than those obtained with either the microwell version 1.0 or microwell version 1.5 test.

Assessment of agreement between the AMPLICOR HIV-1 MONITOR test versions 1.0 and 1.5.

The agreement of the microwell plate AMPLICOR HIV-1 MONITOR version 1.0 (MWP 1.0), the microwell plate AMPLICOR HIV-1 MONITOR version 1.5 (MWP 1.5), and the COBAS AMPLICOR HIV-1 MONITOR version 1.5 (COBAS 1.5) tests was evaluated using clinical specimens and well-characterized control material. Two hundred patient plasma specimens and a panel of known human immunodeficiency virus type 1 (HIV-1) subtypes were tested. All data were log(10) transformed prior to analysis. The 95% limits of agreement for the three tests at the average of 3.66 log(10) copies/ml were +/- 0.28 log(10), +/- 0.34 log(10), and +/- 0.34 log(10) copies/ml for MWP 1.0-MWP 1.5, MWP 1.0-COBAS 1.5, and MWP 1.5-COBAS 1.5, respectively. Ten specimens (6.1%) had differences exceeding the limits of agreement for the MWP 1.0 and MWP 1.5 tests. Correlation coefficients among the three tests were high (r >or=0.96). The viral-load values obtained with the MWP 1.0 test were only 2.1% higher on average than those measured with the MWP 1.5 test and 1.6% higher than those seen with the COBAS 1.5 test. The MWP 1.5 test values were 0.8% higher than the COBAS 1.5 test values. Overall, there was less agreement among the different tests for viral-load values near the lower limit of quantification. The MWP 1.0 test underquantified subtypes A, E, F, G, and H by 1.0 to 2.0 log(10) copies/ml; this problem was not observed with the MWP 1.5 test. The close agreement among the results obtained with the different test versions and formats suggests that it is not necessary to reestablish a baseline viral load when changing AMPLICOR HIV-1 MONITOR tests, unless the patient is known to be infected with a non-B subtype.

Clinical evaluation of two methods for genotyping hepatitis C virus based on analysis of the 5' noncoding region.

We compared the performance characteristics of a standardized direct sequencing method (TRUGENE HCV 5'NC; Visible Genetics Inc., Toronto, Ontario, Canada) and a reverse hybridization line probe assay (INNO-LiPA HCV II; Bayer Corp., Tarrytown, N.Y.) for genotyping of hepatitis C virus (HCV). Both methods are based on detection of sequence heterogeneity in the 5' noncoding (5'NC) region. Concordance between the genotyping methods was assessed by testing 172 samples representing the six major genotypes. Sequence analysis of the more phylogenetically informative nonstructural 5B (NS5B) region was also done with 148 (86%) samples to confirm the accuracy of and resolve discrepancies between the 5'NC genotyping results. The sensitivities of the methods were assessed by using the 5'NC amplicon from both the qualitative and quantitative AMPLICOR HCV tests (Roche Diagnostics Corp., Indianapolis, Ind.). The ability of the methods to detect mixed-genotype infections was determined with mixtures of two different genotypes at relative concentrations ranging from 1 to 50%. Both 5'NC methods were able to genotype 99.4% of the samples with type agreement for 99.5% and subtype agreement for 68.2% of the samples. No or ambiguous subtype results were found by the line probe assay for 16.5% and by the TRUGENE 5'NC test for 17.1% of the samples. Discrepancies occurred between the line probe assay and NS5B results at the type level for 1.4% of the samples and at the subtype level for 14.2% of the samples. Discrepancies also occurred between the TRUGENE 5'NC and NS5B results at the type level for 2% of the samples and at the subtype level for 8.1% of the samples. We also found two distinct strains of HCV classified as type 2 by analysis of the 5'NC region that were type 1 by analysis of the NS5B region. The sensitivities of the two 5'NC genotyping methods were comparable and dependent on the amplification test used ( approximately 10(3) IU/ml with the qualitative HCV RNA tests and approximately 10(5) IU/ml with the quantitative HCV RNA tests). Genotype mixtures were successfully identified at a relative concentration of 5% by the line probe assay and 10% by the TRUGENE 5'NC test. In conclusion, the performance characteristics of the 5'NC methods were similar and both methods produced accurate results at the genotype level but neither method should be used for subtyping.