LCx Assay Research Articles

Chlamydia Positivity in New Orleans Public High Schools, 1996–2005: Implications for Clinical and Public Health Practices

ObjectiveTo describe the trends in chlamydia positivity among New Orleans high school students tested in a schoolwide screening between 1996 and 2005, and to determine factors associated with chlamydia positivity among students during the 10-year period. MethodsBetween school years 1995–1996 and 2004–2005, students in New Orleans public high schools were tested for chlamydia using nucleic acid amplification tests (NAAT) in urine specimens (LCx assay until 1999–2000; BD assay from 2000–2001 to 2004–2005). For each year, we calculated chlamydia positivity by dividing the number of students testing positive by the total number of students tested. Data were analyzed separately by gender. Logistic regressions were performed to determine independent predictors of chlamydia positivity during the 10-year period. ResultsBetween 1996 and 2005, the average chlamydia positivity was 7.0% (95% confidence interval 6.6–7.4) in boys and 13.1% (95% confidence interval 12.6–13.7) in girls (P < .001). Chlamydia detection increased with the switch from LCx to BD assay. In multivariate analyses, chlamydia positivity among boys and girls was significantly associated with age, black race, and gonorrhea coinfection. Additionally, positivity was significantly different by school year among boys (P = .03) and by NAAT used among girls (P = .008). ConclusionsThe trends in chlamydia positivity observed between 1996 and 2005 more likely reflected a high and stable prevalence of chlamydia in the New Orleans school-age adolescent population. Any benefit of screening on individuals tested was likely to be mitigated by participants' uninterrupted social interactions with the dynamic forces that sustain the sexual transmission of chlamydia in the population.

Comparative Evaluation of the Performance of the Abbott Real-Time Human Immunodeficiency Virus Type 1 (HIV-1) Assay for Measurement of HIV-1 Plasma Viral Load following Automated Specimen Preparation

The performance of the new Abbott real-time human immunodeficiency virus type 1 (HIV-1) assay for HIV-1 RNA load determination in plasma was compared to that of the Abbott LCx HIV-1 RNA quantitative assay following automated RNA isolation by the Abbott m1000 extractor. The measured viral loads of 89 clinical specimens differed by mean 0.19 log10 copies/ml (95% confidence interval, 0.12 to 0.26 log10 copies/ml). Although the difference in viral load determinations was positively skewed in favor of the LCx assay, it did not reach statistical significance (P = 0.42). Results were linearly associated (R2 = 0.94) and strongly correlated (R = 0.96). Good performance was observed with HIV-1 subtypes other than B and circulating recombinant forms, although results obtained with two subtype G specimens and one H specimen showed a more substantial difference.

Clinical suspicion as a primary guidance to use commercial amplification tests for rapid diagnosis of pulmonary tuberculosis

The Abbott LCx (Abbott Park, IL) Mycobacterium tuberculosis complex is a commercial amplification assay discontinued from the European market in 2002. A prospective clinical study was carried out to evaluate the clinical utility of the above test as applied by specialists for the rapid diagnosis of active pulmonary tuberculosis (PTB). According to the physician's clinical judgment, patients were classified into 3 groups (low, intermediate, and high) aiming to estimate the probability of active disease. The gold standard for final diagnosis was based on microbiologic and clinical information including data from a 6-month follow-up period. Sensitivities and specificities of rapid microbiologic tests were compared with those based on an integrated approach including clinical evaluation plus the above tests. The incidence of PTB in 214 patients was 13.1%. The basis for initial treatment of PTB was smear-positive results in 46%, positive LCx results in 29%, and clinical suspicion in 18%. For the remaining 7%, therapy was started upon receipt of culture results. The sensitivity, specificity, and positive and negative predictive values of the LCx assay were 68%, 99%, 95%, and 95%, respectively. In comparison, they were 93%, 99%, 96%, and 99%, respectively, for the combination of clinical evaluation plus the LCx test. It is concluded that in patients with high-to-moderate pretest probabilities, the combination of clinical judgment and amplification results strongly enhances a rapid and correct diagnosis of PTB.

Evaluation of the clinical sensitivity for the quantification of human immunodeficiency virus type 1 RNA in plasma: Comparison of the new COBAS TaqMan HIV-1 with three current HIV-RNA assays—LCx HIV RNA quantitative, VERSANT HIV-1 RNA 3.0 (bDNA) and COBAS AMPLICOR HIV-1 Monitor v1.5

The COBAS TaqMan HIV-1 test (Roche Diagnostics) was compared with the LCx HIV RNA quantitative assay (Abbott Laboratories), the Versant HIV-1 RNA 3.0 (bDNA) assay (Bayer) and the COBAS Amplicor HIV-1 Monitor v1.5 test (Roche Diagnostics), using plasma samples of various viral load levels from HIV-1-infected individuals. In the comparison of TaqMan with LCx, TaqMan identified as positive 77.5% of the 240 samples versus 72.1% identified by LCx assay, while their overall agreement was 94.6% and the quantitative results of samples that were positive by both methods were strongly correlated ( r = 0.91). Similarly, in the comparison of TaqMan with bDNA 3.0, both methods identified 76.3% of the 177 samples as positive, while their overall agreement was 95.5% and the quantitative results of samples that were positive by both methods were strongly correlated ( r = 0.95). Finally, in the comparison of TaqMan with Monitor v1.5, TaqMan identified 79.5% of the 156 samples as positive versus 80.1% identified by Monitor v1.5, while their overall agreement was 95.5% and the quantitative results of samples that were positive by both methods were strongly correlated ( r = 0.96). In conclusion, the new COBAS TaqMan HIV-1 test showed excellent agreement with other widely used commercially available tests for the quantitation of HIV-1 viral load.

Comparison of strand displacement and ligase chain amplification for detection of Chlamydia trachomatis infection in urogenital specimens

Two amplification tests for the diagnosis of Chlamydia trachomatis infection, namely the ligase chain reaction (LCx) and the strand displacement assay (ProbeTec), were compared using samples from 1183 patients at sexually transmitted disease clinics. The overall prevalence of positive results was 8.0%, with agreement between the two assays of 98.8%. For endocervical, urethral and male urine samples, agreement was 99.3%, 99.4% and 97.7%, respectively. For ten discrepant samples, alternative amplification assays suggested that the LCx and ProbeTec assays gave erroneous results in six and four cases, respectively. Inhibition of amplification was observed with three (0.25%) urine specimens.

Impact of human immunodeficiency virus type 1 (HIV-1) genetic diversity on performance of four commercial viral load assays: LCx HIV RNA Quantitative, AMPLICOR HIV-1 MONITOR v1.5, VERSANT HIV-1 RNA 3.0, and NucliSens HIV-1 QT.

Human immunodeficiency virus type 1 (HIV-1) evolution and changing strain distribution present a challenge to nucleic acid-based assays. Reliable patient monitoring of viral loads requires the detection and accurate quantification of genetically diverse HIV-1. A panel of 97 HIV-1-seropositive plasma samples collected from Cameroon, Brazil, and South Africa was used to compare the performance of four commercially available HIV RNA quantitative tests: Abbott LCx HIV RNA Quantitative assay (LCx), Bayer Versant HIV-1 RNA 3.0 (bDNA), Roche AMPLICOR HIV-1 MONITOR v1.5 (Monitor v1.5), and bioMérieux NucliSens HIV-1 QT (NucliSens). The panel included group M, group O, and recombinant viruses based on sequence analysis of gag p24, pol integrase, and env gp41. The LCx HIV assay quantified viral RNA in 97 (100%) of the samples. In comparison, bDNA, Monitor v1.5, and NucliSens quantified viral RNA in 96.9%, 94.8%, and 88.6% of the samples, respectively. The two group O specimens were quantified only by the LCx HIV assay. Analysis of nucleotide mismatches at the primer/probe binding sites for Monitor v1.5, NucliSens, and LCx assays revealed that performance characteristics reflected differences in the level of genetic conservation within the target regions.

Use of Ligase Chain Reaction in Early Diagnosis of Tuberculous Meningitis

Introduction: Nucleic acid-based amplification tests are currently licensed only for the detection of Mycobacterium tuberculosis in pulmonary specimens. There are insufficient data for extrapulmonary specimens. The aim of this study is to investigate the diagnostic value of these investigations in tuberculous meningitis. Materials and Methods: We performed a prospective study using a commercial ligase chain reaction DNA amplification technique [Ligase chain result (LCx) M. tuberculosis; Abbott Laboratories, Abbott Park, IL, USA] on cerebrospinal fluid (CSF) to diagnose tuberculous meningitis and compared the results with standard microbiological data. Conflicting cases were resolved according to the final clinical diagnosis. A total of 54 CSF specimens from 54 patients were tested. Results: Six (11.1%) specimens were culture-positive for M. tuberculosis; of these, only 1 (1.9%) was smear-positive. The sensitivity, specificity, positive predictive value and negative predictive value of the LCx assay, compared with culture results, were 66.7%, 100%, 100% and 96%, respectively. After resolution according to clinical data, the sensitivity, specificity, positive predictive value and negative predictive value were 33.3%, 100%, 100% and 75%, respectively. All controls had negative LCx results. There were no false positives. Conclusion: LCx assay is highly specific and complements conventional laboratory diagnostic methods (CSF smear and culture) in the diagnosis of tuberculous meningitis. In the appropriate clinical context, a positive result is strongly suggestive of tuberculosis and could enable antituberculous treatment to be started immediately.

Clinical performance of the LCx ® HCV RNA quantitative assay

This study was conducted to assess the performance of the Abbott laboratories LCx ® HCV RNA Quantitative Assay (LCx assay) in the clinical setting. Four clinical laboratories measured LCx assay precision, specificity, and linearity. In addition, a method comparison was conducted between the LCx assay and the Roche HCV Amplicor Monitor, version 2.0 (Roche Monitor 2.0) and the Bayer VERSANT HCV RNA 3.0 Assay (Bayer bDNA 3.0) quantitative assays. For precision, the observed LCx assay intra-assay standard deviation (S.D.) was 0.060–0.117 log IU/ml, the inter-assay S.D. was 0.083–0.133 log IU/ml, the inter-lot S.D. was 0.105–0.177 log IU/ml, the inter-site S.D. was 0.099–0.190 log IU/ml, and the total S.D. was 0.113–0.190 log IU/ml. The specificity of the LCx assay was 99.4% (542/545; 95% CI, 98.4–99.9%). For linearity, the mean pooled LCx assay results were linear ( r = 0.994) over the range of the panel (2.54–5.15 log IU/ml). A method comparison demonstrated a correlation coefficient of 0.881 between the LCx assay and Roche Monitor 2.0, 0.872 between the LCx assay and Bayer bDNA 3.0, and 0.870 between Roche Monitor 2.0 and Bayer bDNA 3.0. The mean LCx assay result was 0.04 log IU/ml (95% CI, −0.08, 0.01) lower than the mean Roche Monitor 2.0 result, but 0.57 log IU/ml (95% CI, 0.53, 0.61) higher than the mean Bayer bDNA 3.0 result. The mean Roche Monitor 2.0 result was 0.60 log IU/ml (95% CI, 0.56, 0.65) higher than the mean Bayer bDNA 3.0 result. The LCx assay quantitated genotypes 1–4 with statistical equivalency. The vast majority (98.9%, 278/281) of paired LCx assay-Roche Monitor 2.0 specimen results were within 1 log IU/ml. Similarly, 86.6% (240/277) of paired LCx assay and Bayer bDNA 3.0 specimen results were within 1 log, as were 85.6% (237/277) of paired Roche Monitor 2.0 and Bayer specimen results. These data demonstrate that the LCx assay may be used for quantitation of HCV RNA in HCV-infected individuals.

Use of Ligase Chain Reaction for the Rapid Diagnosis of Lymph Node Tuberculosis

Ligase chain reaction amplification (LCx® Abbott Laboratories) was used to detect the presence of M. tuberculosis in 101 adenopathy specimens obtained from 98 patients. A total of 30 cases of lymph node tuberculosis were diagnosed, and the data were compared with results obtained using conventional techniques. The sensitivity of auramine staining and culture were 50.0% and 66.7%, respectively. The sensitivity, specificity, positive predictive value and negative predictive value of the LCx assay were 80.0, 98.6, 96.0, and 92.1% respectively. The results confirm the reliability of ligase chain reaction amplification for the detection of lymph node tuberculosis.

Performance attributes of the LCx ® HCV RNA quantitative assay

The LCx ® HCV RNA quantitative assay (Abbott Laboratories, North Chicago, IL) is designed to use competitive reverse transcriptase-polymerase chain reaction (RT-PCR) and microparticle enzyme immunoassay (MEIA), in combination with a modified Qiagen sample preparation method, to measure the level of hepatitis C virus (HCV) in human plasma and serum. The assay provides quantitative results in international units (IU) of HCV RNA/ml, in copies of HCV RNA/ml, or their log (base 10) equivalents. A conversion study determined that 1 IU equals 4.3 copies. The LCx HCV assay detected HCV RNA transcripts representative of genotypes 1–6 with near equal efficiency. The assay did not cross-react with high concentrations of 21 potentially cross-reactive microorganisms or with 100 HCV-negative specimens. The lower limit of detection was demonstrated to be 23 IU/ml. The LCx assay had similar sensitivity to the Roche Amplicor HCV (version 2.0) qualitative assay when used to test panels containing 6, 12, 23, and 47 IU/ml. The assay linear range was shown to extend from 23 to 2.3 million IU/ml. The intra-assay standard deviation (S.D.) was ≤0.066 log IU/ml for the four HCV positive samples tested, while for the same samples the observed inter-assay S.D. was ≤0.075 log IU/ml. The overall mean assay quantitation value for seven HCV-positive WHO-standardized Acrometrix NAP linearity panel members was within 0.06 log IU/ml of the mean assigned value. The assay was demonstrated to correlate acceptably against the Roche Amplicor HCV monitor test (version 2.0). These data suggest that the assay is standardized appropriately against the WHO standard across its linear range and can be used for quantitation of HCV. In addition, with a sensitivity of 23 IU/ml, the assay can be used to determine if post-therapy viral clearance has occurred.

Reliability of nucleic acid amplification methods for detection of Chlamydia trachomatis in urine: results of the first international collaborative quality control study among 96 laboratories.

The first European Quality Control Concerted Action study was organized to assess the ability of laboratories to detect Chlamydia trachomatis in a panel of urine samples by nucleic acid amplification tests (NATs). The panel consisted of lyophilized urine samples, including three negative, two strongly positive, and five weakly positive samples. Ninety-six laboratories in 22 countries participated with a total of 102 data sets. Of 204 strongly positive samples 199 (97.5%) were correctly reported, and of 506 weakly positive samples 466 (92.1%) were correctly reported. In 74 (72.5%) data sets correct results were reported on all samples, and 17 data sets (16.7%) showed either one false-negative or one false-positive result. In another 11 data sets, two or more incorrect results were reported, and two data sets reported a false-positive result on one negative sample. The Roche COBAS Amplicor test was performed in 44 (43%) data sets, the Abbott LCx assay was performed in 31 (30%) data sets, the Roche Amplicor manual assay was performed in 9 (9%) data sets, an in-house PCR was performed in 9 (9%) data sets, the Becton Dickinson ProbeTec ET assay was performed in 5 (4.9%) data sets, and the GenProbe TMA assay was performed in 4 (3.9%) data sets. The results of the Roche Amplicor manual (95.6% correct), COBAS Amplicor (97.0%), and Abbott LCx (94.8%) tests were comparable (P = 0.48). The results with the in-house PCR, BD ProbeTec ET, and GenProbe TMA tests were reported correctly in 88.6, 98, and 92.5% of the tests, respectively. Freeze-drying of clinical urine specimens proved to be a successful method for generating standardized, stable, and easy-to-transport samples for the detection of C. trachomatis by using NATs. Although the results, especially the specificity, for this proficiency panel were better than most quality control studies, sensitivity problems occurred frequently, underlining the need for good laboratory practice and reference reagents to monitor the performance of these assays.

Early identification of Mycobacterium tuberculosis complex in BACTEC cultures by ligase chain reaction.

A total of 1431 acid-fast bacilli (AFB) in Bactec culture vials from 1427 patients was differentiated by the Bactec NAP method and tested by the LCx Mycobacterium tuberculosis ligase chain reaction system. In all, 1321 of 1325 M. tuberculosis complex (MTBC) isolates were correctly detected by the LCx assay. All the 106 non-tuberculous mycobacteria (NTM) isolates were negative by the LCx assay. No false MTBC-positive result was obtained from NTM isolates. However, the LCx assay failed to detect four MTBC isolates from one patient. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 99.7, 100%, 100% and 96.4%, respectively. These data suggest that the LCx system can be used to identify MTBC in AFB-positive Bactec broth cultures when the growth index is > or = 100. The method gives a 100% PPV and allows a faster turnaround time for MTBC than the NAP test.

LCx Mycobacterium tuberculosis assay is valuable with respiratory specimens, but provides little help in the diagnosis of extrapulmonary tuberculosis

BACKGROUND. Commercial nucleic acid amplification tests, designed for the detection of Mycobacterium tuberculosis DNA/RNA in respiratory samples, are often applied also in nonrespiratory specimens in order to verify the diagnosis of extrapulmonary tuberculosis.AIM. To evaluate the value of the Abbott LCx Mycobacterium tuberculosis assay for the diagnosis of pulmonary and extrapulmonary tuberculosis based on routine clinical laboratory results.METHODS. The assay was used to analyse 350 respiratory and 826 nonrespiratory specimens from 961 patients, of whom 3.6% had culture-proven tuberculosis. The results obtained by the LCx assay were compared with the records on mycobacterial isolates of the national reference laboratory and, in the case of positive findings, with clinical data.RESULTS. In comparison with culture, the sensitivity, specificity and positive/negative predictive value of the assay on respiratory specimens were 87.5%, 99.7%, 93.3% and 99.4%, respectively. With nonrespiratory specimens, the overall sensitivity, specificity and positive/negative predictive value of the LCx assay were 73.3%, 98.0%, 40.7% and 99.5%, respectively. When clinical and histological data were also included, the positive predictive value of LCx with nonrespiratory specimens was 45.8%.CONCLUSION. Critical interpretation of the nucleic acid amplification results obtained from nonrespiratory specimens is necessary in both laboratory and clinical settings.

Is the detection of Mycobacterium tuberculosis DNA by ligase chain reaction worth the cost: experiences from an inner London teaching hospital

Aims—To evaluate the clinical usefulness and the costs of using a rapid, commercial ligase chain reaction test (LCx) to detect Mycobacterium tuberculosis directly from clinical samples. Methods—A prospective study of...

Performance of a multiplex qualitative PCR LCx assay for detection of human immunodeficiency virus type 1 (HIV-1) group M subtypes, group O, and HIV-2.

Early detection of human immunodeficiency virus (HIV) in blood and blood products can be achieved by a sensitive nucleic acid amplification-based assay. We report on the performance of a PCR-based qualitative assay that detects both HIV type 1 (HIV-1) and HIV-2 with a sensitivity of 20 to 50 copies/ml. The assay has a specificity of 99.6% and an inhibition rate of 1.7%. One milliliter of sample is processed with a manifold system and Qiagen columns, and one-third of the extracted sample is used for PCR amplification. An internal control sequence, which is processed and amplified with each sample, monitors for amplification inhibition. Samples are reverse transcribed and are then amplified by reverse transcription-coupled PCR, after which HIV-1- and HIV-2-specific probes are hybridized to the amplified products. Following hybridization, samples are detected in the LCx instrument by microparticle enzyme immunoassay techniques. The detection system has an automated inactivation step that controls for PCR contamination. The HIV-1/2 qualitative RNA assay detects HIV-1 group M subtypes A, B, C, D, E, F, and G and group O. Testing of several HIV-1 seroconversion panels has demonstrated that the HIV-1/2 qualitative RNA assay detects HIV infection on the average of 6 days before p24 antigen can be detected and 11 days before antibodies can be detected.

Ligase chain reaction assay is clinically useful in the discrimination of smear-positive pulmonary tuberculosis from atypical mycobacterioses

We evaluated the usefulness of the ligase chain reaction (LCR) (Abbott LCx Mycobacterium tuberculosis assay) during the initial diagnosis of tuberculosis. LCx was carried out in parallel with conventional methods for the analysis of clinical samples. Out of 86 patients who were examined clinically, 53 were suspected of having pulmonary tuberculosis, eight had residual X-ray scars from previous tuberculosis and 25 served as asymptomatic controls. Ten bronchoscopy samples and 237 sputum samples were analysed by direct microscopy, culture and LCx. All 11 smear-positive and two of three smear-negative tuberculosis patients had at least one LCx-positive specimen. All samples that were both LCx and smear-positive were culture-positive for M. tuberculosis. The smear-positive samples from the five patients with atypical mycobacteriosis were LCx-negative. There were three false-positive results: one in a smear-negative sample from a patient with M. malmoense infection and two from two pneumonia patients. All samples from controls and patients with previous tuberculosis were LCx-negative. The sensitivity, specificity and the positive and negative predictive values of LCx in patient analysis were 92.9%, 95.8%, 81.3% and 98.6%, respectively. LCx assay of M. tuberculosis is useful in rapid confirmation of tuberculosis or atypical mycobacteriosis from a smear-positive sample and may aid in diagnosing smear-negative tuberculosis.

Comparison of Abbott LCx Chlamydia trachomatis Assay With Gen‐Probe PACE2 and Culture

In this study the LCx assay (a nucleic acid amplification assay) for Chlamydia trachomatis in endocervical samples was compared with the Gen‐Probe PACE2 assay (a nucleic acid probe assay) for endocervical samples, and with endocervical culture. In addition, the efficacy of the LCx assay was determined for midstream clean‐catch urine samples because it is often necessary to obtain such a sample for routine urine culture and it is simpler to collect only a single sample without also collecting a first‐void urine for LCx. Endocervical specimens from 205 patients were tested for C. trachomatis via LCx and PACE2. Of these patients, 203 were tested by culture. Midstream cleancatch urine samples from 75 of these patients were tested by LCx. The sensitivities and specificities for these assays, after discrepant analysis, were 100 and 98.9% for LCx of endocervical samples, 52.4 and 100% for PACE2; and 71.4 and 100% for culture. The sensitivity/specificity of LCx for midstream clean‐catch urines was 66.7/98.5%. The apparent prevalence of C. trachomatis in our population was 10.2%. These data indicate that among the methods tested, LCx of endocervical samples had the highest sensitivity for C. trachomatis in this population. The senstivity of the urine LCx assay using midstream clean‐catch collected urines was considerably less than that reported in other studies that used first‐void urines but was higher than that of PACE2. Infect. Dis. Obstet. Gynecol. 8:112–115, 2000.

Multicenter evaluation of the Abbott LCx Mycobacterium tuberculosis ligase chain reaction assay.

Four Australian hospital laboratories evaluated the performance of the Abbott LCx Mycobacterium tuberculosis assay with 2,347 specimens (2,083 respiratory and 264 nonrespiratory specimens) obtained from 1, 411 patients. A total of 152 specimens (6.5%) were culture positive for Mycobacterium tuberculosis complex (MTBC); of these, 79 (52%) were smear positive. After resolution of discrepant data, the overall sensitivity, specificity, and positive and negative predictive values for the LCx assay were 69.7, 99.9, 99.1, and 97.7% respectively. For smear-positive respiratory specimens that were culture positive for MTBC, the values were 98.5, 100, 100, and 98.4%, respectively, while the values for smear-negative respiratory specimens were 41.5, 99.9, 96.4, and 98%, respectively. Relative operating characteristic curves were constructed to demonstrate the relationship between sensitivity and specificity for a range of possible cutoff values in the LCx assay. These graphs suggested that the assay sensitivity for respiratory samples could be increased from 70.2 to 78.6%, while the specificity would be reduced from 99.9 to 99.4% by inclusion of a grey zone (i.e., LCx assay values of between 0.2 and 0.99). An algorithm is presented for the handling of specimens with LCx assay values within this grey zone.

Multicenter evaluation of two commercial amplification kits (Amplicor, Roche and LCx, Abbott) for direct detection of Mycobacterium tuberculosis in pulmonary and extrapulmonary specimens

Direct detection of Mycobacterium tuberculosis was performed in parallel with the Amplicor M. tuberculosis test (Roche Diagnostic System, USA) and the LCx M. tuberculosis (Abbott Diagnostic Division, USA) on 697 samples, collected from 481 patients, in three different Italian laboratories. Though both systems are licensed only for pulmonary specimens, 113 extrapulmonary specimens (represented mainly by pleural fluids, cerebrospinal fluids and urines) were included in the study. Amplification results were compared with acid-fast microscopy, culture, and identification of isolates. Final clinical diagnosis was used to resolve discrepant results. M. tuberculosis was detected in 105 specimens by both assays, whereas 561 were agreeing negatives; 21 and 6 of the remaining true-positive samples scored positive with LCx only and with Amplicor only, respectively. There were three false-positives with LCx and one false-positive with Amplicor. The diagnostic sensitivity of both methods was significantly better when only respiratory specimens were considered (78% versus 59% in nonrespiratory samples with Amplicor, and 88% versus 65% with LCx). Our data reveal a significantly better sensitivity of the LCx ( p = 0.026) and a slight better specificity of the Amplicor assay. It is noteworthy that 16 of the 21 Amplicor-negative specimens in which LCx detected M. tuberculosis were culture negative, thus suggesting that the higher diagnostic sensitivity of the latter assay is attributable to its better analytical sensitivity. However, the majority of such samples originated from patients under antimicrobial treatment, which makes uncertain the clinical significance of such increased sensitivity. Considering true-positive for LCx and true-negative for Amplicor, the 16 culture-negative/LCx-positive/Amplicor-negative specimens resulted true-positives after the resolution of discrepancies, the final overall sensitivity and specificity values of the LCx assay were not significantly different from the ones of the Amplicor assay.

Evaluation of the Abbott LCx Mycobacterium tuberculosis assay for direct detection of Mycobacterium tuberculosis complex in human samples.

Seven hundred thirty-seven clinical samples from 460 patients were processed for direct detection of Mycobacterium tuberculosis complex by a semiautomated ligase chain reaction commercial assay, the LCx Mycobacterium tuberculosis Assay (LCx assay) from Abbott Laboratories. Results were compared to those of direct microscopy and standard microbiological culture. Of 26 patients (5.7%) with a culture positive for M. tuberculosis, 22 (84.6%) were found positive by the LCx assay. The sensitivity of the LCx assay was 98% for smear-positive samples and 27% for smear-negative samples. With an overall culture positivity rate for M. tuberculosis of 8.3% (61 of 737 samples) and after resolution of discrepant results according to clinical data, the sensitivity, specificity, and positive and negative predictive values of the LCx assay were 78, 100, 95, and 98%, respectively, compared to 85, 100, 100, and 98%, respectively, for culture and 67, 99, 87, and 97%, respectively, for acid-fast staining. In conclusion, the LCx assay proved satisfactory and appears to be an easy-to-use 1-day test which must be used with standard culture methods but can considerably reduce diagnosis time versus culture. However, its clinical interest appears to be limited in our population with low mycobacterial prevalence because of its cost considering the small gain in sensitivity versus direct microscopy.