Determination of haemoglobin and prothrombin complex in whole blood using optothermal spectrometry

Optothermal spectrometry measures the thermal energy produced as a result of absorption by molecules at a given modulation frequency and wavelength. Depending on the modulation frequency used, analysis can be performed in very thin layers (50-150 micrometers). A major advantage of optothermal spectrometry is that it is not very sensitive to light scattering. Haemoglobin in whole blood was measured without any reagent at 16 Hz and 2 Hz frequencies. The precisions (within-series, within-day and between-day) were acceptable, and comparisons with reference methods were excellent. As opposed to the reference methods, optothermal spectrometric determinations were not affected by lipaemia. When measured continuously, the signal for haemoglobin increased due to the packing of erythrocytes towards the light source. By converting soluble fibrinogen into insoluble fibrin, the erythrocyte packing could either be inhibited or stopped, and this process could be monitored by assessing the change in the rate of signal increase for haemoglobin. This principle was utilized to analyse the prothrombin complex; the method was found to have acceptable precision and to be comparable to a routine method.