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The microINR System measures prothrombin time (PT) expressed in International Normalized Ratio (INR), for monitoring oral anticoagulant therapy with warfarin.

The microINR System consists of a meter and chips (test strips) and uses fresh capillary whole blood from a fingerstick. The microINR System is intended for patient self-testing use as well as for healthcare professionals at Point of Care settings.

The microINR System is intended for use in patients 18 years old or older. Patients must be stable on warfarin medication for at least 6 weeks before starting to use the microINR System.

For self-testing use: The system is intended for properly trained users under specific prescription of a physician.

Caution: The microINR System is not intended for use in patients who are transitioning from heparin treatment to warfarin therapy. The microINR System is not intended to be used for screening purposes.

The microINR System is comprised of a portable measuring device (microINR, microINR Link and microINR Expert meter) and test strips (microINR Chips) in which the capillary blood sample flows through capillary action.

The microINR Chip contains a reagent in dried form which consists of thromboplastin, and contains two symmetrical regions, the measuring channel and a control channel. The microINR meters measure International Normalized Ratio (INR) based on a Prothrombin Time (PT) assay carried out in the microINR Chip based on microfluidic technology with machine vision detection.

The microINR System has a multi-level On-board Quality Control. Multiple key functions and elements of the system are checked and if deviations are detected, error messages are displayed and test results are not reported.

The microINR System measures prothrombin time (PT) expressed in International Normalized Ratio (INR) for monitoring oral anticoagulant therapy with warfarin.

Here's an analysis of the acceptance criteria and the study that proves the device meets them, based on the provided FDA 510(k) clearance letter:

1. Table of Acceptance Criteria and Reported Device Performance

The document does not explicitly state pre-defined "acceptance criteria" in terms of specific thresholds for slope, intercept, Pearson correlation, SD, or CV%. Instead, it presents the performance characteristics demonstrated by the studies. The comparison to predicate devices, and the conclusion of substantial equivalence, imply that these reported performance values were considered acceptable.

Note: The "Acceptance Criteria (Implied)" are derived from the typical expectations for such medical devices and the fact that these results led to FDA clearance, indicating they met regulatory standards.

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

• Accuracy Study (microINR System vs. Laboratory Reference Device):

  • N: 1016 microINR System results.
  • Data Provenance: Capillary blood samples from control subjects and patients recruited at ten clinical sites. This suggests a prospective collection from multiple geographical locations, though specific countries are not mentioned.

• Accuracy Study (Self-testing patients vs. Laboratory Reference Device):

  • N: 248 INR test results obtained by self-testing patients (compared to laboratory systems).
  • Data Provenance: Collected at seven clinical sites. This also implies prospective data collection.

• Accuracy Study (Self-testing patients vs. Healthcare Professionals using microINR System):

  • N: 461 INR test results.
  • Data Provenance: Collected at seven clinical sites, comparing self-testers to healthcare professionals. This is likely prospective.

• Precision Study (microINR System):

  • N: Duplicate measurements from 502 control subjects and patients.
  • Data Provenance: Performed at ten clinical sites, suggesting prospective collection.

• Precision Study (Trained PSTs):

  • N: Duplicate measurements from 111 patients ("Paired results").
  • Data Provenance: Performed at four clinical sites. Implies prospective collection.

• Precision Study (Untrained PSTs with high INR values):

  • N: Duplicate measurements from 13 patients ("Paired results").
  • Data Provenance: Performed at three clinical sites. Implies prospective collection.

The general provenance is from multiple clinical sites, suggesting a diverse patient population, but specific countries are not detailed. All studies appear to be prospectively collected for the purpose of validating the device performance.

3. Number of Experts Used to Establish the Ground Truth and Qualifications

• The document mentions comparisons to "laboratory systems ACL TOP 500 or ACL TOP 750" as reference methods. These are established laboratory analyzers.
• For the "Accuracy of the microINR System by self-testing patients" study, the comparison also includes "Healthcare professionals (HCP) using the microINR System." While HCPs are involved, specific qualifications beyond their professional role are not detailed for the purpose of establishing a "ground truth" other than operating the device.
• The ground truth for the clinical method comparison studies seems to be based on the results from the ACL TOP 500 or ACL TOP 750 laboratory systems, which are considered the gold standard for PT/INR measurement, rather than human experts adjudicating individual cases.
• The document does not explicitly describe "experts" in the sense of radiologists reviewing images; rather, it refers to standardized laboratory methods and healthcare professionals. Therefore, the specific "number of experts" or their "qualifications" for establishing ground truth, beyond the inherent accuracy of the reference laboratory devices, is not provided.

4. Adjudication Method for the Test Set

No explicit adjudication method (e.g., 2+1, 3+1) is mentioned. Given that the ground truth appears to be established by comparison to highly accurate and standardized laboratory reference instruments (ACL TOP 500/750), a human adjudication process for individual test results is typically not required or described in such device submissions. The comparison is quantitative against these reference devices.

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

No MRMC comparative effectiveness study, detailing how much human readers improve with AI vs. without AI assistance, was performed or presented. This device is a standalone diagnostic system (a meter and test strips) and not an AI-assisted diagnostic tool that aids human interpretation of complex medical images or data. The "readers" in this context are the device users (patients or healthcare professionals), and the study compares their results directly to a laboratory reference, or compares self-testers to healthcare professionals using the same device, rather than measuring an improvement in human diagnostic accuracy with an AI assist.

6. Standalone Performance

Yes, standalone performance was done. The entire set of performance characteristics, particularly the "Accuracy of the microINR System" (comparing the microINR System against a laboratory reference device) and "Precision of the microINR System," represents the standalone performance of the device without explicit human-in-the-loop interpretation beyond operating the device as intended. The system itself measures and displays the INR.

7. Type of Ground Truth Used

The primary ground truth used is comparison to established laboratory reference methods, specifically ACL TOP 500 or ACL TOP 750 laboratory systems, which measure PT/INR from citrate venous plasma samples. This is a highly standardized and accepted method for determining INR.

8. Sample Size for the Training Set

The document does not provide details on a specific "training set" for the device, as it is not an AI/machine learning model in the typical sense that requires a training and a separate test set. The changes implemented are "only SW changes... for increasing the INR measuring range... and the removal of the limitation for LVAD patients," implying a modification to an existing algorithm rather than a completely new, data-trained AI model. The studies presented are for validation of these changes.

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

As noted above, no specific "training set" is mentioned in the context of a machine learning model. The device's underlying principle relies on microfluidic technology and machine vision detection of a prothrombin time assay. The calibration of the chips is done against "International Reference Thromboplastin of the World Health Organization," which serves as a fundamental standard rather than a "ground truth" for a training set in data science terms.

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