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The DensiCHEK™ Plus instrument is intended for use with the VITEK® and VITEK® 2 Systems to measure the optical density of a microorganism suspension. The instrument provides values in McFarland units, proportional to microorganism concentrations. DensiCHEK Plus is indicated for use with polystyrene and glass test tubes and the reading range is 0.0 - 4.0 McFarland. The DensiChek™ Plus has applications as an in vitro diagnostic device.

The DensiCHEK Plus generates a McFarland value using basic colorimetry, which is a method of measurement that relates the amount of color in a transparent medium (liquid) to the amount of a particular substance in the liquid. In general the concentration of the substance being measured is proportional to the intensity of the solution. The darker the color is, the higher the concentration. Absorbance (Abs) is a commonly used measure of the amount of light absorbed by the solution. Absorbance is given by: Abs = - log T or Abs = - log (Ir/10) Where: T = Transmittance Ir = Intensity of light transmitted through the sample 10 = Intensity of light entering the sample The DensiCHEK Plus measures the turbidity of the saline and microorganism suspension using a single wavelength, 580 nm. The absorption of light determines the McFarland value generated by the instrument. The more turbid the suspension is, the higher the McFarland standard measurement. The light source in the DensiCHEK plus is an LED that emits a narrow range of wavelengths, and an interference filter is used between the LED and the test tube (sample) to further narrow the wavelength to 580 nm. There are 2 calibration curves pre-programmed into the DensiCHEK Plus, one for glass tubes and one for plastic tubes. The absorbance is different for glass and plastic, therefore the laboratory technician using the DensiCHEK Plus must choose the appropriate tube type setting for the inoculum suspension based on whether it was prepared in a glass or plastic test tube: The instrument is first zeroed using a test tube filled with saline (blank). The technician then places the well-mixed organism suspension into the instrument and slowly rotates the test tube. The instrument will display a series of dashes followed by a McFarland reading.

The provided document K093224 describes a Special 510(k) Device Modification for the DensiCHEK™ Plus to add VITEK® 2 AST-YS to the list of products for which it can be used. It emphasizes that the device design and fundamental scientific technology were not altered. The submission confirms that the modified device demonstrated substantially equivalent performance to the unmodified device (K083536) during risk assessment studies.

However, the provided text does not contain explicit acceptance criteria or a detailed study report with specific performance metrics and statistical analyses to prove the device meets these criteria. The approval is based on "substantially equivalent performance during risk assessment studies," rather than a detailed performance study with defined criteria.

Given the absence of this information in the provided document, I cannot complete several sections of your request.

Here's a breakdown of what can and cannot be answered based solely on the provided text:

1. A table of acceptance criteria and the reported device performance

Explanation: The document states that the modified device demonstrated "substantially equivalent performance" to the predicate device. However, it does not provide specific numerical acceptance criteria (e.g., accuracy, precision ranges) or detailed performance data against such criteria.

2. Sample size used for the test set and the data provenance (e.g. country of origin of the data, retrospective or prospective)

Not available in the document. The text mentions "risk assessment studies" but does not detail the sample size, type of test sets used, or data provenance.

3. Number of experts used to establish the ground truth for the test set and the qualifications of those experts (e.g. radiologist with 10 years of experience)

Not applicable/available in the document. This device measures optical density (McFarland units) and does not rely on expert interpretation for ground truth establishment. The ground truth for such a device would typically be established by highly calibrated reference instruments or gravimetric methods. This information is not provided.

4. Adjudication method (e.g. 2+1, 3+1, none) for the test set

Not applicable/available in the document. As stated above, this device measures optical density directly, and its performance would be assessed against a known reference, not through an adjudication process involving human experts.

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 an automated optical density measurement instrument, not an AI-assisted diagnostic tool that involves human readers.

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

Yes, implicitly. The DensiCHEK Plus is a standalone instrument that measures turbidity and generates a McFarland value. Its performance evaluation would inherently be standalone, comparing its output to a reference standard. The document states it "demonstrated substantially equivalent performance" which implies standalone performance was evaluated.

7. The type of ground truth used (expert consensus, pathology, outcomes data, etc)

Not explicitly stated in the document. For an optical density measurement device, the ground truth would typically be established by a primary reference method for turbidity/concentration, such as gravimetric analysis or highly calibrated spectrophotometers/densitometers.

8. The sample size for the training set

The document describes a device modification, not the development of a new algorithm that would typically have a "training set" in the context of machine learning. The DensiCHEK Plus uses basic colorimetry and pre-programmed calibration curves. Therefore, this concept of a "training set" in the context of data-driven algorithm development is not applicable here. The calibration curves are likely established during manufacturing and validation, not through a "training set" in the AI sense.

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

As explained above, the concept of a "training set" for an algorithm like an AI model is not applicable to this device's description. The device uses pre-programmed calibration curves established from physical measurements and references, not a machine learning training process with corresponding ground truth data.

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