Method and device for analyzing a body fluid

1. A method for analyzing a body fluid, in particular for blood glucose determination, in which body fluid is applied to a test element for single-use in a test device and the test element is optically coupled to a photometric measuring unit by means of an optical transmission system, the method comprising:

recording a time course of measurements after the body fluid has been applied in order to detect a component of the body fluid on the test element,

monitoring the transmission behavior of the optical transmission system by recording measurements at two different measurement wavelengths, and

determining a difference in the transmission behavior of the optical transmission system before and after applying the body fluid from a wavelength-dependent comparison of the measurements.

2. The method according to claim 1 , wherein a correction of the measurements is carried out or the test result is rejected depending on the difference that is determined.

3. The method according to claim 1 , wherein the two measurement wavelengths are not more than 50 nm away from each other in an absorption range of the test element that is usable for the detection of the component.

4. The method according to claim 1 , wherein one measurement wavelength is in an absorption range of the test element that is usable for detecting the component and the other measurement wavelength lies outside thereof.

5. The method according to claim 1 , wherein a dry blank value is recorded by a measurement before the body fluid is applied to the test element as a measure for the initial transmission behavior of the optical transmission system.

6. The method according to claim 1 , wherein a reference value for the transmission behavior of the optical transmission system is extrapolated from the time course of the measurements at the two measurement wavelengths to a starting time after application of the body fluid.

7. The method according to claim 6 , wherein the reference value is used as an offset correction of the measurements when it is below a predetermined maximum tolerance deviation from the dry blank value.

8. The method according to claim 1 , wherein the measurements recorded in a wavelength-dependent manner are correlated to one another by calculating ratios so that interferences having an effect at both measurement wavelengths are eliminated.

9. The method according to claim 1 , wherein the measurement values are recorded essentially simultaneously at the two measurement wavelengths at time intervals over a predetermined measurement period.

10. The method according to claim 1 , wherein the measurement wavelengths are defined by irradiating spectrally resolved excitation light by means of light-emitting diodes.

11. The method according to claim 1 , wherein at least a part of the optical transmission system is moved and/or deformed in the course of applying the body fluid to the test element.

12. A device for analyzing a body fluid, in particular for blood glucose determination, comprising a portable test device having a photometric measuring unit and a test element coupled to the measuring unit by means of an optical transmission system, where body fluid is applied to the test element for a single-use test, the measuring unit is configured such that the transmission behavior of the optical transmission system is monitored by recording measurements at two different measurement wavelengths, and a difference in the transmission behavior of the optical transmission system is determined before and after applying the body fluid from a wavelength-dependent comparison of the measurements.

13. The device according to claim 12 , wherein the optical transmission system comprises at least one light guide integrated into the test device and/or into the test element.

14. The device according to claim 12 , wherein the optical transmission system has an opto-mechanical coupling device to hold the test element and at the same time to optically couple the test element.

15. The device according to claim 12 , wherein the measuring unit has a light emitter emitting at two measurement wavelengths as a dual emitter, and that a beam combiner uniformly focuses the excitation light irradiated from the light emitter by two light-emitting diodes.