Calibration concept for amperometric creatinine sensor correcting for endogenous modulators

1. A method for calibrating device sensitivity of an enzymatic amperometric device for measuring a concentration of creatinine and/or creatine in a sample comprising one or more enzyme modulators, wherein said device sensitivity is the sensitivity of the device to the sample, the method comprising:

providing an enzyme amperometric device;

providing two or more calibration solutions wherein the two or more calibration solutions comprise creatinine and/or creatine;

measuring device output for the two or more calibration solutions;

determining calibration sensitivities of the device to each of the two or more calibration solutions by calculating a ratio between the output of the device in each of the two or more calibration solutions and a known concentration of creatinine and/or creatine in each of the two or more calibration solutions, wherein each calibration solution has a different amount of enzyme modulator;

determining a degree of modulation for each of the two or more calibration solutions by estimating enzyme modulation based on the amounts of enzyme modulators in each of the two or more calibration solutions;

determining a degree of modulation for the sample to be measured based on the amounts of enzyme modulators in the sample;

calculating the device sensitivity wherein said calculating comprises adjusting the calibration sensitivity of the device to one of the two or more calibration solutions by a factor, and

calibrating the device based on the calculated device sensitivity;

wherein the factor is a function of the determined degree of modulation of the sample and of one of the two or more calibration solutions, and

wherein the calibration sensitivity that is adjusted is the calibration sensitivity of the one or more calibration solutions that has a degree of enzyme modulation closest to the degree of enzyme modulation of the sample.

2. The method of claim 1 , wherein the one or more enzyme modulators include an acid or an alkali or a salt thereof.

3. The method of claim 1 , wherein the one or more enzyme modulators comprise one or more of bicarbonate, acetate, formate, Ca 2+ , Zn 2+ , and pH.

4. The method of claim 1 , wherein said determining a degree of modulation for each of the calibration solutions comprises receiving a value of said degree of modulation.

5. The method of claim 1 , wherein the device is a creatine and/or creatinine sensor, and wherein the device further comprises a membrane covering the device and facing the sample and said function further comprises a ratio between enzyme activity and permeability of the sensor.

6. The method of claim 1 , wherein one of the two or more calibration solutions has a level of enzyme modulation and another calibration solution has a higher level of enzyme modulation.

7. The method of claim 1 , wherein one of the two or more calibration solutions has a level of enzyme modulation.

8. The method of claim 1 , wherein the device is a creatine and/or creatinine sensor.

9. A computer readable medium comprising instructions which when executed by one or more processors of an electronic device, cause the electronic device to operate in accordance with the method as claimed in clam 1 .

10. An electronic device comprising:

one or more processors; and

memory comprising instructions which when executed by one or more of the one or more processors cause the electronic device to operate in accordance with the method claimed in claim 1 .