Fully Automated Optical Hematocrit Measurement From Dried Blood Spots

The impact of the hematocrit (HCT) on the dried blood spot's (DBS) spreading area is one of the most important hurdles which prevents the full acceptance of quantitative microsampling strategies. Several destructive- and non-destructive strategies to assess the HCT from a DBS post-sampling have been presented. Unfortunately, the current methods are either labor-intensive, require a complicated algorithm, or are not automatable. Here, we present a novel setup that permits the fully automated reflectance analysis to measure the HCT from a DBS. The underlying principle is based on the concept presented by Capiau et al. for the non-destructive single-wavelength measurement of the HCT. The novel module was embedded within the DBS-MS 500 platform to enable high-throughput analysis of hematocrit values in combination with automated DBS extraction. The novel setup was assessed and optimized for the probe to card distance, stability, anti-coagulant, spotting volume, scan number, calibration variability, accuracy, and precision. It showed excellent inter-day (≤3.7%) and intra-day (≤1.16%) precision, as well as high accuracy when analyzing authentic samples 101%±7% (range:87%-127%). Besides, the simple and straightforward application of an HCT correction for DBS was demonstrated during a pharmacokinetic study with diclofenac involving three subjects. Thereby, the sample's HCT and the HCT impact on the analyte was assessed and compensated. In conclusion, the novel setup enables quantitative analysis of non-volumetric samples in an automated fashion without compromising the concept of cost-effective, minimally invasive sampling.