Measurement of hematocrit in DBS samples by near-infrared (NIR) spectroscopy

Code: DBS20AS2AT

This project will investigate the possibility to measure the hematocrit value of the dried blood spot (DBS) sample by near-infrared spectroscopy (NIR). This can have an influence on the result, especially when the data are evaluated quantitatively. For this purpose, the results of the NIR measurements will be compared with reference data (Sysmex etc.) obtained simultaneously.

Main Findings

In contrast to established blood sampling strategies (yielding serum or EDTA plasma), DBS consist of whole blood. Therefore, the knowledge about the hematocrit (as percentage of red blood cells) of the DBS sample represents an important parameter especially for quantitative results interpretation. Here, the hematocrit measurement with near-infrared spectroscopy (NIR) from cellulose-based DBS paper represents a valid and reliable approach. After complete drying of the cards, the non-destructive NIR-analysis enables robust hematocrit (Hct) measurements over weeks and presumably months. The correction for the actual hematocrit of the finger prick DBS samples facilitates the accurate correlation to the resulting and comparable plasma levels of the respective drugs. With regard to in-competition DBS sampling, this possibility will enhance the result interpretation significantly. In the present project, different whole blood sampling strategies (venous, finger prick, TAP, Tasso, capillary) and the subsequent hematocrit measurement (Sysmex, NIR, centrifugation) were compared. All measurements for venous EDTA-blood and capillary finger blood (finger prick) were < 10% of relative deviation compared to the ‘true’ Sysmex value. This is also true regardless of the method of measurement. However, collection of capillary blood on heparin (here using the TAP device) and subsequent analysis by NIR led to greater Hct values and a mean relative deviation ˃10%. Transfer to other laboratory is not hindered, because NIR analysis is based on calibration-based technology, which can be adapted and transferred to any other instrument using the same technology. It was additionally shown that the repeated exposure to NIR does not have a measurable impact on the subsequent chemical analysis of the prohibited drugs.