Calibration concept for amperometric creatinine sensor correcting for endogenous modulators

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.