A decreased hemoglobin concentration (tHb) in blood (anemia) is associated with impaired oxygen delivery to organs, which can result in organ damage and heart failure. Currently, tHb analysis requires invasive methods (e.g. a fingerstick), which are time consuming and cause discomfort to the patient. Using optical spectroscopy, the tHb can be estimated by quantifying light absorption in blood. However, the accuracy of current noninvasive optical techniques for tHb quantification is limited by the background attenuation of skin and the unknown blood volume fraction in the total optical probing volume.
Spectroscopic optical coherence tomography (sOCT) allows for quantitative measurements of the optical attenuation in a confined measurement volume, potentially enabling non-invasive estimation of the hemoglobin concentration within individual blood vessels. Although multiple studies have shown that sOCT is capable of quantifying localized oxygen saturation, quantification of the tHb has not yet been reported for physiologically relevant concentrations.
With a home-built visible-light sOCT system we quantified optical attenuation in the visible wavelength range (450–600nm). Implementation of both zero-delay acquisition and focus tracking optimized system sensitivity and ensured that the measured attenuation is only affected by the attenuation of the sample itself.
We validated our method ex-vivo on human whole blood from healthy volunteers (tHb within 12-18 g/dL). The hematocrit was varied to cover the entire pathophysiological range (tHb within 9-21 g/dL) by either dilution with PBS, or plasma removal. Our system quantified the tHb in whole blood throughout the entire pathophysiological range with an accuracy of 10%.