Process Evaluation of a Fully Automated Molecular Diagnostics System

Permanent magnet actuation for magnetic bead-based DNA extraction

BACKGROUND

Recently, automatic molecular diagnostic devices to extract DNA have been extensively developed using magnetic beads. While various methods can be applied to the control of the beads, the efficiency of the control when incorporated in automatic devices has not been studied. This paper proposes a compact magnet actuation method for the control of magnetic beads for DNA extraction, and compares the efficiency to the already available magnetic bead-based DNA extraction device. A permanent magnet was preferred for its compactness, while an electro-magnet provides easy operation. After investigating various methods to actuate the magnet with perspective to the size, circuit complexity, and power requirement, we determined the solenoid actuation method to be most efficient. To further reduce the dimension of the overall actuation device, direct actuation of the permanent magnet to control the hold/release of the beads was employed in this paper. The proposed method was compared with the conventional solenoid actuator with a metal plunger. An experimental fluidics device was set up with a fluidic channel and a syringe pump. The bead holding performance against the fluid speed was tested while a fixed amount of beads was loaded into the center of the channel. The group velocity of the beads was analyzed via image processing to determine whether the magnet was sufficient to hold the beads. The required power and space was analyzed and compared qualitatively and quantitatively.

RESULT

The proposed direct actuation method was capable of holding the beads at faster fluidic speed than the conventional solenoid actuator. The required power was comparable contemplating the high initial power of the solenoid actuator, and required much smaller space since no plunger was needed.

CONCLUSIONS

The direct actuation of the permanent magnet using a solenoid coil showed enhanced performance in holding the beads via permanent magnet, with less complexity of the actuation circuit and space. The proposed method therefore can efficiently improve the overall performance of the bead-based DNA extraction.

Comparison of Workflow, Maintenance, and Consumables in the GeneXpert Infinity 80 and Panther Instruments While Testing for Chlamydia trachomatis and Neisseria gonorrhoeae

BACKGROUND

The 2015 Sexually Transmitted Diseases Treatment Guidelines from the Centers for Disease Control and Prevention recommend testing for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) using nucleic acid amplification tests, and prompt treatment of infected persons on site under direct observation. Faster time to results may enable treatment and management outcomes.

METHODS

Workflow parameters for processing 1, 10, 48, 96, and 192 tests were determined in the GeneXpert Infinity 80 (Cepheid) and Panther (Hologic) instruments.

RESULTS

In an Xpert CT/NG cartridge, the time to first results on the Infinity 80 was 1 hour 30 minutes for single or multiple tests and final results for 10, 48, 96, and 192 tests were available at 1 hour 37 minutes, 1 hour 54 minutes, 3 hour 17 minutes, and 5 hour 7 minutes, respectively. With the Aptima CT/GC assay on the Panther, the respective times were 3 hr 45 min for the first test result, and 3 hour 51 minutes, 4 hour 38 minutes, 5 hour 26 minutes, and 7 hour 4 minutes to final results. The Panther required more time for maintenance and consumed a greater variety of plastics and reagents but required less hands-on time when testing larger numbers of specimens.

CONCLUSIONS

The Infinity 80 is a versatile instrument for continuous random access testing of small or large numbers of clinical specimens and may provide diagnostic results, in some settings, in time for treatment of CT and NG infections.

Comparison of cobas 4800, m2000, Viper XTR, and Infinity 80 Automated Instruments When Processing Urine Specimens for the Diagnosis of Chlamydia trachomatis and Neisseria gonorrhoeae

OBJECTIVES

North American and European advisory groups recommend testing for Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG) with nucleic acid amplification tests. Testing is often performed on automated instruments. The objectives of this study were to process urines for the diagnosis of CT and NG and to examine workflow procedures and outcomes.

METHODS

While processing 1, 24, 48, 96, and 192 urine specimens on 3 batch-mode systems which use 96-well plates: cobas 4800, m2000, and Viper XTR and the random access cartridge testing GeneXpert Infinity 80, we measured assay performance, hands-on time for processing and maintenance, reagents and plastics consumption, time required to obtain results, and testing accuracy.

RESULTS

The Infinity 80 required the least hands-on time for single specimens and smaller batches, whereas the Viper XTR and m2000 required the most hands-on time for all batch sizes. Cumulative daily, weekly, and monthly maintenance was highest for the Viper XTR and lowest for Infinity 80. All batch-mode instruments consumed large amounts of disposables. Time to results was shortest for the Infinity 80, and the Viper XTR provided the shortest time for the batch-mode instruments. All systems showed similar diagnostic accuracy.

CONCLUSIONS

Because detection performances were similar, issues of hands-on time, maintenance, time to results, and consumables are important operational factors for the diagnosis and treatment of CT/NG infections.

Comparison of time-motion analysis of conventional stool culture and the BD MAX™ Enteric Bacterial Panel (EBP)

Background

Conventional bacterial stool culture is one of the more time-consuming tests in a routine clinical microbiology laboratory. In addition, less than 5 % of stool cultures yield positive results. A molecular platform, the BD MAX™ System (BD Diagnostics, Sparks, MD) offers the potential for significantly more rapid results and less hands-on time. Time-motion analysis of the BD MAX Enteric Bacterial Panel (EBP) (BD Diagnostics, Quebec, Canada) on the BD MAX System was compared to conventional stool culture in the microbiology laboratory of a tertiary care pediatric hospital.

Methods

The process impact analysis of time-motion studies of conventional cultures were compared to those of EBP with 86 stool specimens. Sample flow, hands-on time, processing steps, and overall turnaround time were determined and analyzed. Data were obtained and analyzed from both standard operating procedures and direct observation. A regression analysis was performed to ensure consistency of measurements. Time and process measurements started when the specimens were logged into the accessioning area of the microbiology laboratory and were completed when actionable results were generated.

Results

With conventional culture, negative culture results were available from 41:14:27 (hours:minutes:seconds) to 54:17:19; with EBP, positive and negative results were available from 2:28:40 to 3:33:39.

Conclusions

This study supports the suggestion that use of the EBP to detect commonly encountered stool pathogens can result in significant time savings and a shorter time-to-result for patients with acute bacterial diarrhea.

Clinical performance of the BD Onclarity HPV assay using an adjudicated cohort of BD SurePath liquid-based cytology specimens

OBJECTIVES

To compare the performance of the BD Onclarity HPV Assay (BD Diagnostics, Sparks, MD) in BD SurePath liquid-based cytology media with that of Hybrid Capture 2 (HC2, Qiagen, Germantown, MD) samples co-collected in specimen transport medium in an adjudicated patient cohort.

METHODS

The performance of the BD Onclarity HPV Assay using BD SurePath media was compared with that of HC2 samples co-collected in specimen transport medium using 541 archived samples from a multicenter US clinical trial with histologically adjudicated cervical biopsy specimens.

RESULTS

The sensitivity for cervical intraepithelial neoplasia (CIN) 2 positivity (n - 104) was 90.4% (95% confidence interval [CI], 83-95) and 93.3% (95% CI, 87-97) and specificity was 76.9% (95% CI, 73-81) and 77.8% (95% CI, 74-82) for the BD assay and HC2, respectively. Nine cases of CIN 2+ had results discordant with the high-risk HPV assay. All were found to have been correctly classified with the BD assay using a novel WAVE denaturing high-performance liquid chromatography double-stranded DNA sequencing method.

CONCLUSIONS

The clinical performance of The BD Onclarity HPV Assay with respect to histology end points was similar to HC2. Moreover, discordant analysis revealed improved performance of the BD assay with respect to ability to provide extended genotyping information and lack of cross-reactivity with low-risk HPV types associated with cellular abnormalities. The relative risks for CIN 3 disease for HPV 31 and HPV 33/58 (combined) were comparable to that of HPV 18 in this population, suggesting that these genotypes may warrant monitoring in future studies.

Process evaluation of an open architecture real-time molecular laboratory platform

The needs of molecular diagnostic laboratories that perform both Food and Drug Administration-cleared as well as laboratory-developed tests are usually not met on a single analytical platform. Furthermore, little information is available about the direct impact of molecular automation on labor costs and efficiency in clinical laboratories. We performed a process impact analysis from time and motion studies of a novel molecular diagnostic robotic system designed to automate sample preparation, extraction, and analysis. All 27 preanalytical tasks were quantified for the amount of time spent preparing 24 specimens for analysis. These steps were completed in 899 s (14 min, 59 s) followed by 7887 s (131 min, 27 s) of instrument operation independent of operator control (walk-away time). Postanalytical results evaluation required 1 min per specimen. The instrument automatically extracted the nucleic acid from the specimen, added the eluted DNA to the amplification reagents, and performed the analysis. Only 12% of the total instrument operations required relatively unskilled human labor. Thus, the availability of automated molecular diagnostic instruments will facilitate the expansion of molecular testing in the clinical laboratory because they reduce operator costs with respect to time and complexity of the tasks they are asked to perform.

Workflow and maintenance characteristics of five automated laboratory instruments for the diagnosis of sexually transmitted infections

The choice of a suitable automated system for a diagnostic laboratory depends on various factors. Comparative workflow studies provide quantifiable and objective metrics to determine hands-on time during specimen handling and processing, reagent preparation, return visits and maintenance, and test turnaround time and throughput. Using objective time study techniques, workflow characteristics for processing 96 and 192 tests were determined on m2000 RealTime (Abbott Molecular), Viper XTR (Becton Dickinson), cobas 4800 (Roche Molecular Diagnostics), Tigris (Hologic Gen-Probe), and Panther (Hologic Gen-Probe) platforms using second-generation assays for Chlamydia trachomatis and Neisseria gonorrhoeae. A combination of operational and maintenance steps requiring manual labor showed that Panther had the shortest overall hands-on times and Viper XTR the longest. Both Panther and Tigris showed greater efficiency whether 96 or 192 tests were processed. Viper XTR and Panther had the shortest times to results and m2000 RealTime the longest. Sample preparation and loading time was the shortest for Panther and longest for cobas 4800. Mandatory return visits were required only for m2000 RealTime and cobas 4800 when 96 tests were processed, and both required substantially more hands-on time than the other systems due to increased numbers of return visits when 192 tests were processed. These results show that there are substantial differences in the amount of labor required to operate each system. Assay performance, instrumentation, testing capacity, workflow, maintenance, and reagent costs should be considered in choosing a system.

Evaluation of a new DNA test for detection of carcinogenic human papillomavirus

Using archived specimens, we evaluated a new automated real-time PCR assay (BD Diagnostics) that detects all carcinogenic human papillomaviruses (HPV) and provides HPV genotyping for seven of them, including HPV16 and HPV18, the two most carcinogenic HPV genotypes. We found comparable results with Hybrid Capture 2 (HC2) for detection of carcinogenic HPV (n = 473) and with Linear Array and Line Blot Assay (n = 371) for detection of individual HPV genotypes.