Hematocrit-Independent Sampling Enables White Blood Cell Counts from Patterned Dried Blood Spot Cards.

Area of Science:

• Biomedical Engineering
• Clinical Diagnostics
• Point-of-Care Testing

Background:

• Accurate white blood cell (WBC) counts are crucial for patient health monitoring and disease diagnosis.
• Current WBC testing requires access to clinical laboratories, limiting accessibility for home-bound or remote populations.
• Traditional dried blood spot (DBS) cards lack accuracy and precision for WBC counts due to sample variability.

Purpose of the Study:

• To develop and validate a novel patterned dried blood spot (pDBS) card for accurate and reproducible WBC quantification.
• To overcome the limitations of conventional DBS cards in measuring WBC counts.
• To enable accessible, at-home blood collection for WBC testing.

Main Methods:

• Developed a pDBS card with metered volume collection zones.
• Collected whole blood (75 μL) and allowed it to dry on the pDBS cards.
• Quantified WBC counts using qPCR to measure the 18S rRNA gene in the metered blood volumes.

Main Results:

• The pDBS card reproducibly metered blood volumes (12.1 μL, 7.8% CV) across a hematocrit range of 25-55%.
• WBC counts obtained using the pDBS method were comparable to results from a HemoCue point-of-care analyzer.
• The pDBS method demonstrated improved accuracy and precision over standard DBS cards.

Conclusions:

• The pDBS card offers a reliable method for accurate WBC count determination from dried blood samples.
• This technology has the potential to significantly improve access to essential blood testing for underserved populations.
• pDBS cards facilitate at-home blood sampling, expanding diagnostic capabilities beyond clinical settings.