(90 days)
The LIAISON PLEX Yeast Blood Culture (BCY) Assay is a qualitative nucleic acid multiplex in vitro diagnostic test intended for use on the LIAISON PLEX System for simultaneous detection and identification of multiple potentially pathogenic fungal organisms in positive blood culture. The LIAISON PLEX BCY Assay is performed directly on blood culture samples identified as positive by a continuous monitoring blood culture system and which contain fungal organisms as determined by Gram Stain. The LIAISON PLEX BCY Assay detects and identifies the following fungal organisms:
Candida albicans
Candida auris
Candida dubliniensis
Candida famata
Candida glabrata
Candida guilliermondii
Candida kefyr
Candida krusei
Candida lipolytica
Candida lusitaniae
Candida parapsilosis
Candida tropicalis
Candida haemulonii / duobushaemulonii
Cryptococcus neoformans / gattii
The detection and identification of specific fungal nucleic acids from individuals exhibiting signs and/or symptoms of bloodstream infection aids in the diagnosis of bloodstream infection when used in conjunction with other clinical information. The results from LIAISON PLEX BCY Assay are intended to be interpreted in conjunction with Gram stain results and should not be used as the sole basis for diagnosis, treatment management decisions.
Negative results in the setting of a suspected bloodstream infection with pathogens that are not detected by this test. Positive results do not rule out co-infection with other organisms; the organism(s) detected by LIAISON PLEX BCY Assay may not be the definite cause of disease. Additional laboratory testing (e.g. sub-culturing of positive blood cultures for identification of organisms not detected by LIAISON PLEX BCY Assay, susceptibility testing and differentiation of mixed growth) and clinical presentation must be taken into consideration in the final diagnosis of bloodstream infection.
The LIAISON PLEX "Yeast Blood Culture Assay (BCY Assay) is performed directly on blood culture media using blood culture bottles identified as positive by a continuous monitoring blood culture system, and which contain a fungal organism, as determined by a Gram stain. The system consists of an instrument, a single-use disposable test cartridge, and a transfer pipette. The user loads the sample into the sample port of the LIAISON PLEX Yeast Blood Culture Assay Cartridge. Next, the user sets up the sample order on the LIAISON PLEX System by first entering the sample information or scanning the barcode ID located on the sample tube, then scanning the barcode ID located on the test cartridge. Last, the user inserts the test cartridge into the processing module to initiate the test. The LIAISON PLEX System identifies the assay being run and automatically initiates the proper testing protocol to process the sample, analyze the data, and generate test results.
The LIAISON PLEX System automates the BCY Assay sample analysis through the following steps: a) Sample Preparation: Nucleic acid extraction via mechanical and chemical cell lysis and magnetic bead-based nucleic acid isolation; b) Amplification: Multiplex PCR based amplification of the extracted nucleic acid to generate target specific amplicons; c) Hybridization: Amplified DNA hybridizes to specific capture DNA arrayed on a glass slide in a microarray format and the bound target DNA, in turn, hybridizes with mediator and gold-nanoparticle probes; d) Signal Analysis: Gold nanoparticle probes bound specifically to target-containing spots in the microarray are silver-enhanced, and light scatter from the spots is measured and further analyzed to determine the presence (Detected) or absence (Not Detected) of a target.
Acceptance Criteria and Device Performance for LIAISON PLEX Yeast Blood Culture Assay
The LIAISON PLEX Yeast Blood Culture (BCY) Assay is a qualitative nucleic acid multiplex in vitro diagnostic test for the simultaneous detection and identification of multiple potentially pathogenic fungal organisms in positive blood cultures. The study summarized below aimed to demonstrate the device meets its acceptance criteria through analytical and clinical performance evaluations.
1. Table of Acceptance Criteria and Reported Device Performance
The acceptance criteria for the LIAISON PLEX BCY Assay clinical study were predefined as:
- Sensitivity: ≥ 90% for all targets
- Specificity: ≥ 95% for each target
- Failure rate: ≤ 15%
The clinical performance data, combining prospective and pre-selected specimens, is summarized in the table below, comparing it against the acceptance criteria.
Table 1: LIAISON PLEX BCY Assay Clinical Performance (Acceptance Criteria vs. Reported Performance)
| Pathogen Target | Acceptance Criteria (Sensitivity) | Reported Sensitivity/PPA (Combined) | Acceptance Criteria (Specificity) | Reported Specificity/NPA (Combined) | Overall Failure Rate (Initial Run) | Overall Failure Rate (After Retest) | Acceptance Criteria (Failure Rate) |
|---|---|---|---|---|---|---|---|
| Candida albicans | ≥ 90% | 100.0% (34/34) | ≥ 95% | 99.0% (97/98) | 2.9% (Overall) | 0.2% (Overall) | ≤ 15% |
| Candida auris | ≥ 90% | 100.0% (4/4) | ≥ 95% | 100.0% (128/128) | |||
| Candida dubliniensis | ≥ 90% | NA (0/0) | ≥ 95% | 100.0% (132/132) | |||
| Candida famata | ≥ 90% | NA (0/0) | ≥ 95% | 100.0% (132/132) | |||
| Candida glabrata | ≥ 90% | 100.0% (46/46) | ≥ 95% | 100.0% (86/86) | |||
| Candida guilliermondii | ≥ 90% | NA (0/0) | ≥ 95% | 100.0% (132/132) | |||
| Candida haemulonii/C. duobushaemulonii | ≥ 90% | NA (0/0) | ≥ 95% | 100.0% (132/132) | |||
| Candida kefyr | ≥ 90% | 100.0% (1/1) | ≥ 95% | 100.0% (131/131) | |||
| Candida krusei | ≥ 90% | 100.0% (4/4) | ≥ 95% | 100.0% (128/128) | |||
| Candida lipolytica | ≥ 90% | NA (0/0) | ≥ 95% | 100.0% (132/132) | |||
| Candida lusitaniae | ≥ 90% | 100.0% (2/2) | ≥ 95% | 100.0% (130/130) | |||
| Candida parapsilosis | ≥ 90% | 100.0% (17/17) | ≥ 95% | 99.1% (114/115) | |||
| Candida tropicalis | ≥ 90% | 100.0% (6/6) | ≥ 95% | 97.6% (123/126) | |||
| Cryptococcus neoformans/Cryptococcus gattii | ≥ 90% | 100.0% (5/5) | ≥ 95% | 100.0% (127/127) |
NA = Not applicable, as there were no positive cases for this target in the combined prospective/pre-selected dataset to calculate sensitivity, or no negative cases to calculate specificity.
The reported performance demonstrates that the LIAISON PLEX BCY Assay met all defined acceptance criteria.
2. Sample Sizes Used for the Test Set and Data Provenance
The test set for the clinical performance evaluation utilized a combination of prospective, pre-selected, and contrived specimens:
- Prospective Specimens (Clinical Study): 69 unique specimens from four geographically diverse clinical sites in the United States. These were collected prospectively between June 2023 and October 2023. One initial specimen was excluded due to an inconclusive Gram stain result.
- Pre-selected Specimens (Clinical Study): 63 remnant, de-identified specimens sourced from 6 different sites/vendors in the United States. The data provenance is retrospective clinical specimens that were pre-characterized.
- Contrived Specimens: 829 specimens were artificially generated. These were blinded, randomized, and tested at all four testing sites during June 2023. These are contrived data.
3. Number of Experts Used to Establish Ground Truth for the Test Set and Qualifications
The provided document does not explicitly state the number of experts or their specific qualifications (e.g., radiologist with 10 years of experience) used to establish the ground truth for the test set.
However, the ground truth for the clinical study was established by comparing the LIAISON PLEX BCY Assay's performance against a Standard of Care culture followed by identification by Matrix Assisted Laser Desorption/Ionization coupled to time-of-flight Mass Spectrometry (MALDI-TOF MS) for all fungal targets. For the pre-selected specimens, it is mentioned that they were "characterized by an FDA cleared molecular assay prior to enrollment in the study." This implies that the ground truth relied on established laboratory methodologies and potentially an FDA-cleared reference method.
4. Adjudication Method for the Test Set
The document does not describe an adjudication method like "2+1" or "3+1" using human experts for the clinical study. The comparison was made against a "Standard of Care culture followed by identification by MALDI-TOF MS" as the reference method, which serves as the definitive ground truth for the presence and identification of the fungal organisms. For the pre-selected specimens, an "FDA cleared molecular assay" was used for characterization prior to study entry. These are objective laboratory methods rather than subjective expert interpretations requiring adjudication.
5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study was done
No, a Multi-Reader Multi-Case (MRMC) comparative effectiveness study was not reported. This device is an in vitro diagnostic (IVD) assay designed for automated detection and identification of fungal organisms directly from blood culture samples. Its performance is evaluated against laboratory reference methods (culture and MALDI-TOF MS, or existing molecular assays), not against human reader interpretation of images or other subjective assessments. Therefore, there is no discussion of how human readers improve with or without AI assistance, as AI assistance is not part of the described use case for this IVD device.
6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) was done
Yes, the performance presented for the LIAISON PLEX BCY Assay in the analytical and clinical performance sections is for the standalone algorithm/device performance directly on the sample, without human interpretation or intervention in the diagnostic output. The system automates sample analysis, including nucleic acid extraction, amplification, hybridization, and signal analysis, to generate detected or not detected results. The indication for use clearly states the results are "intended to be interpreted in conjunction with Gram stain results and should not be used as the sole basis for diagnosis, treatment management decisions," but this refers to the clinical application context, not a human-in-the-loop for the device's fundamental diagnostic accuracy calculation.
7. The Type of Ground Truth Used
The primary ground truth used for the clinical study was:
- Standard of Care culture followed by identification by Matrix Assisted Laser Desorption/Ionization coupled to time-of-flight Mass Spectrometry (MALDI-TOF MS). This is a laboratory-based, objective method for identifying microorganisms.
- For pre-selected specimens, ground truth was established by an previously FDA-cleared molecular assay.
- For contrived specimens, the ground truth was inherently known based on how the samples were prepared (spiking known organisms).
8. The Sample Size for the Training Set
The document does not report specific sample sizes for a separate training set for this device. The information provided heavily details analytical and clinical verification/validation (test set) studies. For diagnostic devices like this (nucleic acid assays), the development process typically involves extensive analytical characterization (Limit of Detection, Inclusivity, Exclusivity, Interference, Reproducibility) and then clinical validation. It is probable that internal development, optimization, and early verification studies used various sets of samples, but these are not explicitly termed "training sets" in the context of machine learning model training as one might expect for AI/ML-based diagnostic software.
9. How the Ground Truth for the Training Set Was Established
As no explicit "training set" is documented (in the context of AI/ML), there is no description of how ground truth was established for such a set. However, for the analytical studies and development of the assay, ground truth would have been established through well-characterized reference strains and clinical isolates, quantified using standard microbiology techniques (e.g., CFU/mL for Limit of Detection). These methods involve culturing, molecular characterization, and established laboratory practices to confirm the identity and concentration of the microorganisms.
§ 866.3365 Multiplex nucleic acid assay for identification of microorganisms and resistance markers from positive blood cultures.
(a)
Identification. A multiplex nucleic acid assay for identification of microorganisms and resistance markers from positive blood cultures is a qualitative in vitro device intended to simultaneously detect and identify microorganism nucleic acids from blood cultures that test positive by Gram stain or other microbiological stains. The device detects specific nucleic acid sequences for microorganism identification as well as for antimicrobial resistance. This device aids in the diagnosis of bloodstream infections when used in conjunction with other clinical and laboratory findings. However, the device does not replace traditional methods for culture and susceptibility testing.(b)
Classification. Class II (special controls). The special control for this device is FDA's guideline document entitled “Class II Special Controls Guideline: Multiplex Nucleic Acid Assay for Identification of Microorganisms and Resistance Markers from Positive Blood Cultures.” For availability of the guideline document, see § 866.1(e).