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The cobas 8000 ISE module is a fully automated ion-specific analyzer intended for the in vitro potentionetric determination of chloride, potassium, and sodium in serum, plasma, and urine ion-selective electrodes. Measurements obtained by this device are used in the diagnosis and treatment of diseases or conditions involving electrolyte imbalance.

The cobas 8000 ISE module is an Ion-Selective Electrode (ISE) system for the determination of sodium, potassium, and chloride in serum, plasma, and urine. The cobas 8000 ISE module and the ISE Gen 2 reagents were previously cleared for serum and plasma sample types under K100853 and urine sample type on K123726. This premarket notification seeks to obtain FDA review and clearance for the urine sample type for the ISE Gen 2 reagents on the cobas 8000 ISE module using an expanded measuring range for sodium and chloride analytes at the low end of the measuring range and the new calibration method cleared in K132418. An ISE makes use of the unique properties of certain membrane materials to develop an electrical potential (electromotive force, EMF) for the measurements of ions in solution. The electrode has a selective membrane in contact with both the test solution and an internal filling solution. The internal filling solution contains the test ion at a fixed concentration. Because of the particular nature of the membrane, the test jons will closely associate with the membrane on each side. The membrane EMF is determined by the difference in concentration of the test ion in the test solution and the internal filling solution. The EMF develops according to the Nernst equation for a specific ion in solution (see package insert for further explanation). Please refer to K 100853 for detailed hardware and software information relating to the cobas 8000 modular analyzer series.

This document describes the performance of the cobas 8000 ISE Indirect Na, K, Cl for Gen. 2 device, specifically focusing on its use for urine samples with an expanded measuring range for sodium and chloride.

1. Acceptance Criteria and Reported Device Performance

The device performance is compared to a predicate device (cobas 8000 ISE Module using Low/High/Serum Compensator calibration cleared under K123726) and a reference method (flame photometry for Na and K, coulometry for Cl). The acceptance criteria are implicitly demonstrated by showing substantial equivalence to the predicate device and by meeting established performance metrics for analytical devices (repeatability, intermediate precision, linearity, detection limits).

Notes on Acceptance Criteria:

• The document implies that the device meets acceptance criteria if its performance is substantially equivalent to the predicate device and the reference methods, and if the within-run precision (repeatability), total precision (intermediate precision), and detection limits are within acceptable analytical limits for clinical chemistry devices.
• For the expanded measuring range for Sodium and Chloride (20-59.9 mmol/L), the acceptance criteria are demonstrated by the stated precision (repeatability and intermediate precision) within that new range.
• The high correlation coefficients (e.g., 0.9995 for Sodium to reference method) and slopes close to 1 with small intercepts indicate good agreement with the reference methods and predicate.

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

• Test Set Sample Sizes for Method Comparison Studies:
  • Sodium:
    • Method Comparison to Reference (flame photometer): N = 106
    • Method Comparison to Predicate: N = 92
  • Potassium:
    • Method Comparison to Reference (flame photometry): N = 99
    • Method Comparison to Predicate: N = 92
  • Chloride:
    • Method Comparison to Reference (coulometry): N = 100
    • Method Comparison to Predicate: N = 92
• Data Provenance: The document does not explicitly state the country of origin of the data. The "Date Prepared: May 8, 2014" and the submitter being Roche Diagnostics (Indianapolis, IN, USA) with manufacturing in Mannheim, Germany (K100853 reference), suggests an international context, but the specific location of sample collection for the studies is not specified. The studies appear to be prospective as they are conducted to demonstrate the performance of the candidate device for a 510(k) submission.

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

This type of analytical device (Ion-Selective Electrode system for chemical determination) relies on established reference methods (e.g., flame photometry, coulometry) rather than expert interpretation of images or clinical cases. Therefore, the concept of "experts establishing ground truth" in the way it applies to diagnostic imaging or clinical decision support systems is not directly applicable here. The "ground truth" is typically defined by the accurate results obtained from the reference methods, which are performed by trained laboratory personnel following standardized protocols. No specific number or qualification of "experts" for ground truth establishment is mentioned, as it's an analytical performance study.

4. Adjudication Method for the Test Set

Not applicable. As noted above, this is an analytical performance study of a laboratory device measuring chemical analytes, not a diagnostic interpretation task requiring adjudication of results from multiple observers.

5. If a Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study Was Done

No. An MRMC study is relevant for diagnostic devices that involve human interpretation (e.g., radiologists reading images). This device is an automated in vitro diagnostic instrument; its performance is evaluated through analytical studies, not human reader performance.

6. If a Standalone (Algorithm Only Without Human-in-the-Loop Performance) Was Done

Yes, the studies presented are standalone performance evaluations. The data provided (repeatability, intermediate precision, method comparison, detection limits) are direct measurements of the instrument's analytical capabilities without human intervention in the measurement process itself, beyond standard laboratory operation and quality control.

7. The Type of Ground Truth Used

The ground truth for the method comparison studies was established using reference methods:

• Sodium: Flame photometer
• Potassium: Flame photometry
• Chloride: Coulometry

For repeatability, intermediate precision, and detection limit studies, the "ground truth" is intrinsic to the statistical analysis of the measurements themselves, often against a known concentration of controls or calibrators.

8. The Sample Size for the Training Set

The document does not explicitly mention a "training set" in the context of machine learning. This device is an automated analytical instrument based on established electrochemical principles (Ion-Selective Electrodes) and conventional calibration methods, not an AI/ML-based device that learns from a training dataset in the same way. The instrument is "trained" or calibrated using "ISE Standard Low, High, High" (LHH) calibrators, which are commercially available standards with known concentrations. The exact number of calibrator measurements for system calibration or "training" (in the sense of instrument calibration) is not provided but is typically specified by the manufacturer's protocol.

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

Not applicable as an AI/ML training set. The "ground truth" for the device's calibration refers to the assigned values of the calibrator materials (ISE Standard Low, High, High). These values are established by the manufacturer, typically through highly accurate and traceable reference methods, and are verified for consistency and accuracy. The document mentions that "Aqueous ISE standards Low and High were cleared under K053165. The LHH calibration scheme was cleared under K132418," indicating that the standards themselves and the calibration methodology have been previously reviewed and deemed acceptable.

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