A Sensor for the Non-invasive Determination of Hemoglobin in Sampling Tubes

Continuous, online and non-invasive monitoring of critical blood parameters such as the concentration of hemoglobin (ctHb) is of great value for clinical applications. The absorption spectrum of hemoglobin, of its derivatives as well as of its plasma dominates the optical properties of whole blood in the visible and infrared bands. In the present work a novel sensor is introduced that uses two wavelengths in the infrared range of the electromagnetic spectrum to determine the concentration of hemoglobin in whole blood. The described device can be used to measure ctHb of blood in sampling tubes, used for drainage systems or during a blood donation session. To avoid interference with the oxygenation status of the blood the measurement wavelength is selected at isosbestic points. Measurements are compared to an invasive reference method. The described set-up allows for detecting hemoglobin concentrations ranging up to 16.5 g/dL. Since light is subjected to scattering when traveling through whole blood, resulting in a bias, the sensor is calibrated empirically. In the present study tubes from three different manufacturers are used. Within the above mentioned range the sensor exhibits an accuracy (ARMS, root-mean-square difference between measured values and reference values) of 0.84.