METHOD AND APPARATUS FOR BACKGROUND CURRENT ARRANGEMENTS FOR A BIOSENSOR

• US 20070135696A1
• Filed: 11/14/2006
• Published: 06/14/2007
• Est. Priority Date: 11/22/2005
• Status: Active Grant

• Current Assignee: Konamite Limited
• Original Assignee: Isense Corporation
• Inventors: Ward, W.
• Granted Patent: US 7,729,737 B2
• Time in Patent Office: Days
• US Class Current: 600/345
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1486 using enzyme electrodes, e.g. with immobilised oxidase

Abstract

Embodiments of the present invention provide for raising a background current setting for a biosensor above the actual (measured) background current present (i.e., overestimating the background current), particularly in the hypoglycemic range, to improve sensor accuracy and decrease the chance of glucose value overestimation by the sensor.

Claims

1. A method, comprising:

determining an initial background current value of an analyte sensor;

determining for the analyte sensor in use an initial analyte sensor output value using the initial background current value;

adjusting the initial background current value by a factor based on the determined initial analyte sensor output value to form an adjusted background current value; and

forming an adjusted analyte sensor output value using the adjusted background current value.

2. The method of claim 1, wherein said factor is a multiplication factor applied to the initial background current value.

3. The method of claim 2, wherein said multiplication factor is less than 3.

4. The method of claim 1, wherein said factor comprises an increase or decrease of the initial background current value to an adjusted background current value selected from a predefined list of acceptable adjusted background current values.

5. The method of claim 4, wherein said predefined list of acceptable adjusted background current values comprises 0, 0.8, 1.5, 2.2, and 3.0 nA.

6. The method of claim 1, wherein the adjusted background current value is greater than the initial background current value.

7. The method of claim 1, wherein said based on the initial analyte sensor output value comprises determining whether the initial analyte sensor output value falls within a predetermined range.

8. The method of claim 7, wherein said predetermined range is 70 mg/dl and below.

9. The method of claim 8, wherein said adjusted background current value is approximately 1.3-1.7 nA.

10. The method of claim 7, wherein said predetermined range is above 70 mg/dl.

11. The method of claim 10, wherein said adjusted background current value is approximately 0.6-1.0 nA.

12. The method of claim 1, wherein said determining an initial background current value comprises providing an arbitrary background current level within a range of approximately 0.5 to 2.0 nA.

13. The method of claim 1, wherein said adjusted analyte sensor output value is displayed on an associated display device.

14. The method of claim 1, wherein said adjusted background current value is further adjusted in real time as the adjusted analyte sensor output value changes.

15. The method of claim 1, wherein said using the initial background current value comprises subtracting the initial background current value from a first measured analyte sensor output value to form said initial analyte sensor output value, and said using the adjusted background current value comprises subtracting the adjusted background current value from a second measured analyte sensor output value to form said adjusted analyte sensor output value.

16. An apparatus comprising:

a storage medium having stored therein a plurality of programming instructions designed to enable the apparatus, when the programming instructions are executed, to determine an initial background current value of an analyte sensor, determine for the analyte sensor in use an initial analyte sensor output value using the initial background current value, adjust the initial background current value by a factor based on the determined initial analyte sensor output value to form an adjusted background current value, and form an adjusted analyte sensor output value using the adjusted background current value; and

a processor coupled to the storage medium to execute the plurality of programming instructions.

17. A method, comprising:

subtracting a first background current value of an analyte sensor from a first analyte sensor output value to form a first net analyte sensor output value;

obtaining a capillary glucose value of an individual;

dividing the first net analyte sensor output value by the capillary glucose value to form a sensitivity value;

determining a second background current value of the analyte sensor;

determining for the analyte sensor a second analyte sensor output value using the second background current value;

adjusting the second background current value by a factor based on the determined second analyte sensor output value to form a third background current value;

subtracting the third background current value from the second analyte sensor output value to form a second net analyte sensor output value; and

dividing the second net analyte sensor output value by the sensitivity value to form an estimated glucose value.

18. The method of claim 17, wherein said sensitivity value is formed from a time-weighted series of previous net analyte sensor output values and previous capillary blood glucose values.

19. A method for obtaining an analyte value of a sample using an analyte sensor, comprising:

determining a fixed background current value to be used for the analyte sensor;

bringing the analyte sensor into contact with the sample to form an initial analyte sensor current value;

subtracting the fixed background current value from the initial analyte sensor current value to form a net analyte sensor current value;

dividing the net analyte sensor current value by a sensitivity value of the analyte sensor to form an estimated glucose value; and

displaying said estimated glucose value if said estimated glucose value is above a predefined threshold, and applying a reducing factor if said estimated glucose value is at or below said predefined threshold to form an adjusted glucose value and then displaying said adjusted glucose value.

20. The method of claim 19, wherein said fixed background current value is from 0.0 nA to 10 nA.

21. The method of claim 19, wherein said sensitivity value is determined by dividing the net analyte sensor output value by a measured capillary glucose value.

22. The method of claim 19, wherein said predefined threshold is 90 mg/dl.

23. The method of claim 19, wherein said applying a reducing factor comprises applying a reducing factor of approximately 15% or less to said estimated glucose value.