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The T2Bacteria Panel run on the T2Dx Instrument is a qualitative T2 Magnetic Resonance (T2MR) test for the direct detection of bacterial species in K2EDTA human whole blood specimens with suspected bacteremia. The T2Bacteria Panel identifies six species of bacter baumannii, Enterococus faccium, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus.

The T2Bacteria Panel is indicated as an aid in the diagnosis of bacteremia and results should be used in conjunction with other clinical and laboratory data. Concomitant blood cultures are necessary to recover organisms for susceptibility testing or further identification and for organisms not detected by the T2Bacteria Panel.

Results from the T2Bacteria Panel are not intended to be used as for diagnosis, treatment, or other patient management decisions in patients with suspected bacteremia.

The T2Bacteria Panel detects and identifies six bacterial target species directly from whole blood specimens and independent of blood culture using nucleic acid amplification and proprietary T2MR detection technology. The assay is performed on the proprietary T2Dx platform. The whole blood specimen, drawn into a blood collection tube containing K₂EDTA is used for the test. The blood collection tube containing a minimum of 3 mL of blood is loaded directly onto the T2Dx instrument as part of the assembled Cartridge, a single use self-contained unit that contains all of the reagents and disposables required to run a single test. Fully automated on the T2Dx, the blood specimen is mixed with the Lysis Reagent to lyse the red blood cells and the bacterial cells are concentrated by centrifygation. The Internal Control is added to the concentrated bacterial cells, which then undergo a bead beating step to lyse the bacteria cells. The supernatant containing the DNA from the lysed bacterial cells and the Internal Control are amplified with the target and Internal Control specific primers. The generated amplicon is then aliquoted into individual tubes containing target specific conjugated particles for Acinetobacter baumannii, Enterococcus faecium, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and the Internal Control. These individual tubes are read in the MR reader and a signal is generated.

Up to seven specimens can be loaded onto the T2Dx Instrument in parallel. When running a single specimen, the first result is reported in 3.5 hours from the specimen is loaded onto the instrument. The results are interpreted using the T2Dx applications software as valid or invalid, and if valid, target specific results are reported as Positive or Target not Detected. For one target, the Escherichia coli channel, results are reported as Positive, Indeterminate, or Target not Detected. An Indeterminate result is a valid result, but the presence or absence of Escherichia coli cannot be definitively assessed, and the indeterminate status applies only to the Escherichia coli channel. Results are displayed on the T2Dx touchscreen and can be printed. Raw T2MR data are not available to the end user.

Here's a summary of the acceptance criteria and study details for the T2Bacteria Panel, specifically concerning the addition of Acinetobacter baumannii detection:

Acceptance Criteria and Device Performance for Acinetobacter baumannii

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The T2Biothreat Panel is a qualitative, multiplexed, nucleic acid-based in vitro diagnostic test intended for use with the T2Dx Instrument. The T2Biothreat Panel detects nucleic acids from the following organisms directly from K2EDTA whole blood samples:

1. Bacillus anthracis (plasmids pXO1 and pXO2)
2. Francisella tularensis
3. Burkholderia spp. (B. mallei/B. pseudomallei)
4. Yersinia pestis
5. Rickettsia prowazekii

The T2Biothreat Panel will not distinguish between detection of Burkholderia mallei and Burkholderia pseudomallei but will present valid detections as a positive detection of Burkholderia species.

The T2Biothreat Panel is intended to test individuals with signs and symptoms of infection from biothreat agents and/or individuals who are at risk for exposure or may have been exposed to these agents. The T2Biothreat Panel is indicated as an aid in the diagnosis of anthrax, tularemia, melioidosis, glanders, typhus fever and plague in response to suspected or confirmed bioterrorism events or outbreaks. Diagnosis of infection must be made in conjunction with clinical, epidemiologic and other laboratory data. Results are for the presumptive identification of Bacillus anthracis, Francisella tularensis, Burkholderia spp. (B. mallei), Yersinia pestis and Rickettsia prowazekii. Results are meant to be used in conjunction with other clinical, epidemiologic, and laboratory data, in accordance with the guidel by the relevant public health authorities. The definitive identification of Bacillus anthracis, Francisella tularensis, Burkholderia mallei, Burkholderia pseudomallei, Yersinia pestis or Rickettsia prowazekii requires additional testing and confirmation procedures in consultation with the appropriate public health authorities for whom reports may be required. Positive results do not rule out co-infections with pathogens not included on the T2Biothreat Panel. Negative results do not preclude infection with the biothreat microbial agents targeted by the device and should not be used as the sole basis for diagnosis, treatment, or other patient management decisions.

The T2Biothreat Panel is indicated for use in laboratories that have the appropriate biosafety equipment, personal protective equipment (PPE), containment facilities, and personnel trained in the safe handling of clinical specimens potentially containing biothreat organisms.

The T2Biothreat Panel is indicated for use in laboratories that follow public health guidelines that address appropriate biosafety conditions, interpretation of test results, and coordination of findings with public health authorities.

This assay is not FDA-cleared or approved for testing blood or plasma donors.

The T2Biothreat Panel is a qualitative, multiplexed, nucleic acid-based in vitro diagnostic test intended for use with the T2Dx Instrument. The T2Biothreat Panel detects nucleic acids from the following organisms directly from K2EDTA whole blood samples: Bacillus anthracis (plasmids pXO1 and pXO2), Francisella tularensis, Burkholderia spp. (B. mallei/B. pseudomallei), Yersinia pestis, and Rickettsia prowazekii. The T2Biothreat Panel is run on the T2Dx, a fully automated, benchtop instrument. During processing on the T2Dx, intact pathogen cells are concentrated directly in whole blood, then lysed to release the target DNA. After amplification, target amplicon is hybridized with superparamagnetic particles and then detected by T2MR. The Internal Control on the T2Biothreat Panel monitors performance for each sample. The T2Biothreat Panel is a qualitative molecular diagnostic assay that employs whole blood compatible PCR amplification followed by T2 Magnetic Resonance (T2MR) detection. The T2Biothreat Panel is performed on the T2Dx Instrument, which executes all steps after specimen loading, with the capability of loading up to seven blood specimens at the same time. Individually, a KeEDTA whole blood specimen containing a minimum of 3 mL is loaded directly onto the T2Biothreat Sample Inlet, which is then placed on the T2Biothreat Cartridge along with the T2Biothreat Reagent Tray. The Cartidge and Reagent Tray contain the lysis reagent, internal control, primers, enzyme, buffer and probe-coupled superparamagnetic particles for each detected tarqet. After loading into the T2Dx. the blood specimen is mixed with the red blood cell lysing reagent and the bacterial cells and human cellular debris are concentrated by centrifygation. The internal control is added to the concentrated pellet and a bead-beating process lyses the bacterial cells. The supernatant containing the DNA from the lysed bacterial cells and the internal control is amplified using the target and internal control-specific primers. The generated amplified product is aliquoted into individual tubes containing target-specific probe conjugated particles for each detected target and the internal control. The amplified to target-specific probes attached to superparamagnetic particles causing clustering of the particles. The hybridization occurring in individual tubes is analyzed in the T2MR reader and a signal for each target is generated, which indicates the presence of the target organism(s). This automated process is the same process followed by the FDA cleared T2Candida and T2Bacteria Panels performed on the T2Dx Instrument system. When running a single specimens simultaneously, the first specimen will be reported in approximately 4 hours from the specimen is loaded onto the instrument. The results are interpreted by the device software as valid or invalid (based on the result of the internal control or target detections), and if valid, results are reported as "Positive" or "Target not Detected" for each specific target.

Here's a breakdown of the acceptance criteria and study information for the T2Biothreat Panel, based on the provided text:

Acceptance Criteria and Device Performance

Study Information

The provided document describes standalone performance studies for the T2Biothreat Panel. It does not mention any multi-reader multi-case (MRMC) comparative effectiveness study.

2. Sample Sizes and Data Provenance

• Test Set (Clinical Performance):
  • Negative Arm: Undisclosed number of K2EDTA whole blood samples from healthy donors (no signs/symptoms of infection) and febrile donors (fever ≥ 100.4 °F).
  • Positive Arm: Sequence-verified clinical bacterial strains spiked into whole blood collected from febrile donors. The sample sizes for the positive arm are listed as:
    • B. anthracis (pXO1 & pXO2): 6 (

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The T2Bacteria Panel run on the T2Dx Instrument is a qualitative T2 magnetic resonance (T2MR) test for the direct detection of bacterial species in K2EDTA human whole blood specimens with suspected bacteremia. The T2Bacteria Panel identifies five species of bacteria: Enterococcus faecium, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus.

The T2Bacteria Panel is indicated as an aid in the diagnosis of bacteremia and results should be used in conjunction with other clinical and laboratory data. Concomitant blood cultures are necessary to recover organisms for susceptibility testing or further identification, and for organisms not detected by the T2Bacteria Panel.

Results from the T2Bacteria Panel are not intended to be used as the sole basis for diagnosis, treatment management decisions in patients with suspected bacteremia.

The T2Bacteria Panel detects and identifies five bacterial target species directly from whole blood specimens and independent of blood culture using nucleic acid amplification and proprietary T2MR® detection technology. The assay is performed on the proprietary T2Dx platform.

The whole blood specimen, drawn into a blood collection tube containing K₂EDTA is used for the test. The blood collection tube containing a minimum of 3 mL of blood is loaded directly onto the T2Dx instrument as part of the assembled Cartridge, a single use self-contained unit that contains all of the reagents and disposables required to run a single test.

Fully automated on the T2Dx, the blood specimen is mixed with the Lysis Reagent to lyse the red blood cells and the bacterial cells are concentrated by centrifugation. The Internal Control is added to the concentrated bacterial cells, which then undergo a bead beating step to lyse the bacteria cells. The supernatant containing the DNA from the lysed bacterial cells and the Internal Control are amplified with the target and Internal Control specific primers. The generated amplicon is then aliquoted into individual tubes containing targetspecific conjugated particles for Enterococcus faecium, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and the Internal Control. These individual tubes are read in the MR reader and a signal is generated.

Up to seven specimens can be loaded onto the T2Dx Instrument in parallel. When running a single specimen, the first result is reported in 3.5 hours from the time the specimen is loaded onto the instrument. The results are interpreted using the T2Dx applications software as valid or invalid, and if valid, target specific results are reported as Positive or Target not Detected. For one target, the Escherichia coli channel, results are reported as Positive, Indeterminate, or Target not Detected. An Indeterminate result is a valid result, but the presence or absence of Escherichia coli cannot be definitively assessed, and the indeterminate status applies only to the Escherichia coli channel. Results are displayed on the T2Dx touchscreen and can be printed. Raw T2MR data are not available to the end user.

Here's a breakdown of the acceptance criteria and study information for the T2Bacteria Panel, based on the provided text:

1. Acceptance Criteria and Reported Device Performance

The document does not explicitly state "acceptance criteria" for the clinical study in a dedicated table format. However, it presents the performance metrics (PPA and NPA) for each target species. We can infer the implicit acceptance criteria from these reported values, typically striving for high sensitivity (PPA) and specificity (NPA). For the purpose of this response, I will list the reported performance from the combined prospective and contrived arms as the "reported device performance."

Note: PPA (Sensitivity) was calculated against samples with titer levels at or above the limit of detection (LoD) in the Contrived Arm and blood culture positives in the Prospective Arm. NPA (Specificity) was calculated from all samples (including below LoD and unspiked negative samples) as the total number of negative channels divided by total number of non-spiked channels in the Contrived Arm and blood culture negatives in the Prospective Arm.

2. Sample Size Used for the Test Set and Data Provenance

• Prospective Arm: 1,427 subjects tested. The study was conducted at eleven sites within the US. The data is prospective.
• Contrived Arm: 250 contrived specimens (50 strains of each of the five bacterial species) and an additional 100 blood samples not spiked with T2Bacteria Panel members. These were evaluated at three sites. The data is contrived (laboratory-prepared).

3. Number of Experts Used to Establish the Ground Truth for the Test Set and the Qualifications of Those Experts

The document does not explicitly state the number of experts or their qualifications used to establish the ground truth for the test set.

For the Prospective Arm, the ground truth was "the reference method of blood culture," with species identification performed on all positive bacteria cultures using methods like Gram stain, bioMerieux Vitek® 2, bioMerieux or Bruker MALDI TOF, and PCR. This implies standard laboratory professionals and potentially clinicians reviewed and confirmed results, but specific details on expert involvement for ground truth establishment are not provided.

For the Contrived Arm, the ground truth was established by spiking known concentrations of bacterial species into healthy donor whole blood. This is a controlled, laboratory-defined ground truth, not reliant on expert interpretation for "truth" but rather on the setup of the experiment.

4. Adjudication Method for the Test Set

The document does not explicitly state an adjudication method (such as 2+1, 3+1, etc.) for establishing ground truth from the blood cultures in the clinical study. It refers to "species identification was performed on all positive bacteria cultures and methods included Gram stain, bioMerieux Vitek® 2, bioMerieux or Bruker MALDI TOF, and PCR." Discordant analysis for T2(+)/BC(-) cases was performed, identifying "strong evidence of infection" based on other blood cultures or sequencing, or "other evidence of infection" from non-blood cultures, but this is a reconciliation process rather than an initial ground truth adjudication.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done, If So, What Was the Effect Size of How Much Human Readers Improve with AI vs. Without AI Assistance

Not applicable. This device is a diagnostic test (T2Bacteria Panel) that directly detects bacterial species using T2 magnetic resonance technology. It is not an AI-assisted diagnostic tool for human readers; it provides a direct result. Therefore, no MRMC comparative effectiveness study involving human readers improving with or without AI assistance was performed.

6. If a Standalone (i.e., algorithm only without human-in-the-loop performance) Was Done

Yes, this was a standalone performance study. The T2Bacteria Panel is an automated diagnostic instrument. "Results are interpreted using the T2Dx applications software as valid or invalid, and if valid, target specific results are reported as Positive or Target not Detected." The clinical performance evaluation directly compares the device's results to blood culture results. There isn't a human-in-the-loop component for interpreting the T2Bacteria Panel's output described in the document.

7. The Type of Ground Truth Used (Expert Consensus, Pathology, Outcomes Data, Etc.)

The primary ground truth used was blood culture results with species identification. For the contrived arm, the ground truth was the known spiked bacterial species and concentrations.

For the discordant analysis of T2(+)/BC(-) results, additional forms of evidence were used to assess the likelihood of a true positive, which included:

• Other blood cultures positive for the same organism within ±14 days.
• Sequencing of concurrently drawn blood samples.
• Other non-blood matrices cultured positive for the same organism within ±14 days.

8. The Sample Size for the Training Set

The document does not explicitly mention a separate "training set" for the T2Bacteria Panel. This is typically a characteristic of machine learning models. For a molecular diagnostic assay like this, development usually involves analytical studies to optimize reagents and parameters (LoD, specificity, etc.), rather than a distinct "training set" in the machine learning sense. The performance data presented (LoD, Reproducibility, Inclusivity, Exclusivity, Competitive Inhibition, Interfering Substances) represent analytical validation studies.

9. How the Ground Truth for the Training Set Was Established

As no explicit "training set" is mentioned in the machine learning context, this question is not applicable. The ground truth for analytical validation studies (which could be considered analogous to development/optimization) was established through controlled laboratory experiments, such as spiking known organisms at specific concentrations into whole blood.

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T2Candida 1.1 Panel and T2Dx Instrument is a qualitative T2 Magnetic Resonance (T2MR) assay for the direct detection of Candida species in K2EDTA human whole blood specimens from patients with symptoms of, or medical conditions predisposing the patient to, invasive fungal infections. The T2Candida 1.1 Panel identifies five species of Candida and categorizes them into the following three species groups:

1. Candida albicans and/or Candida tropicalis
2. Candida parapsilosis
3. Candida glabrata and/or Candida krusei
   The T2Candida 1.1 Panel is indicated for the presumptive diagnosis of candidemia. The T2Candida 1.1 Panel is performed independent of blood culture. Concomitant blood cultures are necessary to recover organisms for susceptibility testing or further identification. The T2Candida QCheck Positive and T2Dx QCheck Negative External Controls are intended to be used as quality control samples with the T2Candida 1.1 Panel when run on the T2Dx Instrument. These controls are not intended for use with other assays or systems.

The T2Candida 1.1 Panel run on the T2Dx® Instrument is a qualitative T2 Magnetic Resonance (T2MR®) assay for the direct detection of Candida species in EDTA human whole blood specimens from patients with symptoms of, or medical conditions predisposing the patient to, invasive fungal infections. The T2Candida Panel identifies five species of Candida and categorizes them into the following three groups:

• 1. Candida albicans and/or Candida tropicalis,
• 2. Candida parapsilosis
• 3. Candida qlabrata and/or Candida krusei
     The T2Candida 1.1 Panel does not distinguish between C. albicans and C. tropicalis. The T2Candida 1.1 Panel does not distinguish between C. glabrata and C. krusei. The T2Candida Panel is indicated for the presumptive diagnosis of candidemia. The T2Candida Panel is performed independent of blood culture. Concomitant blood cultures are necessary to recover organisms for susceptibility testing or further identification. The T2Candida positive (T2Candida QCheck) and negative External Controls (T2Dx QCheck) are intended to be used as quality control samples with the T2Candida 1.1 Panel when run on the T2Dx Instrument. These controls are not intended for use with other assays or systems. The T2Candida 1.1 Panel utilizes magnetic resonance-based detection (T2®MR technology) to qualitatively detect the same five species of Candida direct from K2EDTA-treated human whole blood. The T2Candida 1.1 Panel, run on the T2Dx instrument, performs sample concentration and Candida target DNA amplification for direct detection of species-specific amplicon. The test incorporates an Internal Control (IC) for monitoring test performance. The workflow for T2Candida 1.1 Panel is the same as the original cleared test and can only be performed on the T2Dx instrument, a bench-top, automated sample-to-result system, which performs all steps in the test after specimen loading. A design change was made to remove two foil-sealed tubes containing calcium hypochlorite ("bleach tubes") from the T2Candida Cartridge configuration and modify the software to remove the bleach transfer steps from the T2Dx workflow.

Here's an analysis of the acceptance criteria and study findings for the T2Candida 1.1 Panel, based on the provided text:

1. Acceptance Criteria and Reported Device Performance

• A/T Channel: 100.0 (97.1-100.0)
• P Channel: 99.2 (95.7-99.9)
• K/G Channel: 99.2 (95.7-99.9)
• Overall: 99.5 (98.1-99.9)
  Compared favorably to the predicate (T2Candida Panel DEN140019) specificity. |
  | Improved Product Stability (ability to achieve acceptable shelf-life) | Product shelf-life demonstrated at 8 months, with studies ongoing to extend it. Stability issues observed with the predicate panel due to bleach byproducts were mitigated. |

2. Sample Size and Data Provenance

• Test Set Sample Size: Not explicitly stated as a single number. Two specificity studies were conducted, each involving:
  • Human whole blood pooled from healthy donors.
  • Samples triple-spiked with high titer (100 CFU or 1000 CFU) of Candida species (C. albicans, C. parapsilosis, C. glabrata or C. tropicalis, C. parapsilosis, C. krusei).
  • Negative samples were human whole blood from the same pool without spiking.
  • Samples were loaded such that Negative Samples and Positive APG or TPK were positioned in adjacent drawers.
• Data Provenance: The studies appear to be conducted internally by the manufacturer (T2 Biosystems, Inc.) in a controlled laboratory setting. The origin of the healthy donor whole blood is not specified (e.g., country of origin). The studies are retrospective modifications to an existing device, validating the changes.

3. Number of Experts and Qualifications

This information is not provided in the text. The study focuses on laboratory performance metrics (specificity, stability) rather than human interpretation or expert-adjudicated ground truth.

4. Adjudication Method

This information is not applicable/provided in the text. The device is a qualitative diagnostic assay, and the study evaluates its direct detection performance against known spiked concentrations. There's no mention of human adjudication of results.

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

• No MRMC study was done. The device is a standalone diagnostic panel, not one designed for human-in-the-loop assistance. The study focuses on the device's technical performance.

6. Standalone Performance

• Yes, a standalone performance study was done. The specificity studies described directly evaluate the T2Candida 1.1 Panel's ability to accurately detect Candida species (or their absence) in blood samples, without human intervention in the diagnostic process beyond sample loading and result interpretation.

7. Type of Ground Truth Used

• Known Spiked Samples: The ground truth for the specificity studies was established by preparing blood samples with known concentrations (high titer: 100 CFU or 1000 CFU) of specific Candida species or known negative (unspiked) blood samples. This is a form of controlled laboratory spiking to simulate infection.

8. Sample Size for Training Set

• Not explicitly provided. The document describes a Special 510(k) submission for a modified version (1.1) of an already cleared device. It states the fundamental scientific technology and principle of operation are equivalent to the original T2Candida Panel (cleared as DEN140019). Information regarding the training set for the original algorithm or the 1.1 update is not presented in this document.

9. How Ground Truth for Training Set Was Established

• Not explicitly provided. As with the training set size, this document focuses on the validation of the modified device. Details on how the ground truth was established for the original algorithm's development (training) are not included.

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The T2Candida Panel and T2Dx® Instrument is a qualitative T2 Magnetic Resonance (T2MR®) assay for the direct detection of Candida species in EDTA human whole blood specimens from patients with symptoms of, or medical conditions predisposing the patient to, invasive fungal infections. The T2Candida Panel identifies five species of Candida and categorizes them into the following three species groups:

1. Candida albicans and/or Candida tropicalis,
2. Candida parapsilosis
3. Candida glabrata and/or Candida krusei

The T2Candida Panel does not distinguish between C. albicans and C. tropicalis. The T2Candida Panel does not distinguish between C. glabrata and C. krusei.

The T2Candida Panel is indicated for the presumptive diagnosis of candidemia. The T2Candida Panel is performed independent of blood culture. Concomitant blood cultures are necessary to recover organisms for susceptibility testing or further identification.

The T2Candida positive and negative External Controls are intended to be used as quality control samples with the T2Candida Panel when run on the T2Dx® instrument system. These controls are not intended for use with other assays or systems.

The T2Candida panel and T2Dx® Instrument is comprised of the T2Candida Panel performed on the T2Dx® Instrument. The T2Candida Panel is a qualitative molecular diagnostic assay that employs a whole blood compatible PCR amplification followed by T2 magnetic resonance (T2MR) detection. The T2Candida Panel is performed on the T2Dx Instrument which executes all steps after specimen loading. A K2 EDTA whole blood specimen is loaded onto the T2Candida Sample Inlet, which is then placed on the T2Candida Base along with the T2Candida Reagent Pack. The Reagent Pack contains the internal control, amplification reagent, enzyme and the probe-coupled superparamagnetic particles for each Candida target. Three milliliters of the blood specimen is transferred to the T2Dx® Instrument where lysis of the red blood cells, concentration and lysis of the Candida cells and amplification of the Candida DNA takes place. Amplification products are detected by T2MR detection using species-specific probes which are attached to the superparamagnetic particles. At the end of each assay, the T2Dx® Instrument uses a bleach solution to neutralize all liquids on the cartridge to mitigate the risk of amplicon contamination. The assay provides an identification of Candida albicans and/or Candida tropicalis, Candida parapsilosis, and Candida glabrata and/or Candida krusei. The test does not distinguish between C. albicans and C. tropicalis. The test does not distinguish between C. glabrata and C. krusei.

Acceptance Criteria and Device Performance Study for T2Candida Panel and T2Dx® Instrument

1. Table of Acceptance Criteria and Reported Device Performance

The provided document does not explicitly present a table of acceptance criteria in numerical values for clinical performance metrics (like minimum desired PPA/NPA). Instead, it describes various studies and their results, implying that these results were deemed acceptable for market clearance. For the purpose of this response, I will interpret "acceptance criteria" as the performance metrics that were reported and considered satisfactory by the FDA for the device to be classified.

2. Sample sizes used for the test set and data provenance

• Test Set (Clinical Study - Contrived Samples):

  • Sample Size: 250 positive contrived samples (50 isolates for each of the five Candida targets, spiked at specific concentrations) + 50 negative unspiked blood specimens = 300 total samples.
  • Data Provenance: The human blood specimens were collected from patients at three clinical sites in K2EDTA tubes. These specimens were then transported to T2 Biosystems for preparation of contrived samples. The prepared samples were de-identified and shipped to testing sites. The data is thus a mix of prospective (blood collection) and contrived (spiking) for the positive samples, and prospective for the negative samples. The isolates used for spiking were obtained from a reference laboratory and a clinical laboratory (US, implicitly).

• Test Set (Clinical Study - Prospective Samples):

  • Sample Size: 1501 blood specimens from adult patients.
  • Data Provenance: Prospective. Specimens were collected at nine geographically diverse sites.

3. Number of experts used to establish the ground truth for the test set and their qualifications

The document does not explicitly state the number or qualifications of experts used to establish the ground truth for the test set.

• For the Contrived Samples: The "ground truth" (presence and concentration of Candida species) was established through controlled laboratory spiking (colony count testing) and sequencing of isolates. This is an analytical determination, not typically requiring expert consensus on diagnosis.
• For the Prospective Samples: The "ground truth" for candida presence/absence was primarily established by blood culture results, which is a standard laboratory reference method. The identification of isolates was confirmed by sequence analysis of the ITS2 region. While a clinical microbiologist or pathologist would interpret these results, the document does not specify a panel of experts for adjudication.

4. Adjudication method for the test set

• For the Contrived Samples: No formal adjudication method involving multiple human readers is described for the contrived samples. The ground truth was based on the known spiking composition and verified colony counts. Discrepancies (e.g., initial LoD not validated) led to retesting.
• For the Prospective Samples: The "gold standard" was blood culture. For false positive T2Candida results (where blood culture was negative), a chart and case history review was conducted. This review process itself can be seen as a form of clinical adjudication, attempting to find clinical evidence supporting or refuting the T2Candida result when the primary reference method (blood culture) disagreed. However, the document does not specify an "adjudication method" in the sense of a consensus panel (e.g., 2+1, 3+1).

5. If a multi-reader multi-case (MRMC) comparative effectiveness study was done, If so, what was the effect size of how much human readers improve with AI vs without AI assistance

No. A multi-reader multi-case (MRMC) comparative effectiveness study involving human readers or AI assistance was not conducted or described. The T2Candida Panel and T2Dx® Instrument is a molecular diagnostic assay that provides a direct result for Candida species; it is not an image-based AI device that would typically involve human readers interpreting AI output.

6. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done

Yes. The studies described for the T2Candida Panel and T2Dx® Instrument represent standalone (algorithm only) performance. The device fully automates the processing and analysis steps after manual specimen loading, and "the T2Dx® Instrument reports a positive or negative result for each detection channel." The performance metrics (sensitivity, specificity, PPA, NPA, precision, LoD, etc.) are all indicative of the device's inherent capability to detect Candida species from whole blood without real-time human interpretation or modification of its direct output.

7. The type of ground truth used

• For Analytical Studies (Precision, LoD, Analytical Sensitivity, Co-infection, Analytical Specificity): The ground truth was established by controlled laboratory preparation of samples with known Candida species and concentrations, verified by colony count testing and sequence analysis of isolates. Negative controls were known to be free of Candida.
• For Clinical Studies (Contrived Samples): The ground truth was established by controlled laboratory spiking of blood specimens with specific, verified Candida isolates at known concentrations. Negative samples were unspiked blood.
• For Clinical Studies (Prospective Samples): The ground truth for the presence or absence of Candida infection was primarily based on blood culture results, which is a widely accepted laboratory reference standard for candidemia. For "false positives" by T2Candida where blood culture was negative, chart and case history review was used to provide further context.

8. The sample size for the training set

The document does not explicitly specify a "training set" in the context of machine learning model development. For molecular diagnostic assays like the T2Candida Panel, the development process typically involves extensive analytical studies to establish assay design, primer/probe specificity, cutoff values, and performance characteristics, rather than training a machine learning algorithm on a distinct dataset.

However, the assay cut-off values (Table 12) for the T2MR signal were established using a "limit of blank study" with negative blood specimens from 113 healthy and 39 unhealthy patients (total 152 samples), tested with two different reagent lots. This serves a similar purpose to training data for setting a threshold.

9. How the ground truth for the training set was established

As noted above, there isn't a "training set" in the traditional machine learning sense. However, the ground truth for establishing the assay cut-off (analogous to a threshold used in training) was:

• Negative blood specimens: Confirmed to be negative for Candida (implied by sourcing from healthy/unhealthy patients and used to determine the upper limit of T2 signal distribution for negative measurements).
• Positive internal control measurements: Used to determine the lower limit of T2 signal for positive internal controls. The internal control itself is a known DNA sequence amplified and detected within each sample.

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