For whole blood, which approach can be used with slight modifications (pre-wetting first)?

• A. Forward mode with pre-wetting first
• B. Reverse mode with warming
• C. Forward mode with no modification
• D. Reverse mode with pre-wetting

Answer: (A)

When a viscous sample like whole blood moves through a porous analytical medium, how the liquid wets the surface and the direction it travels through the medium matter a lot. Pre-wetting fills the pores and removes air gaps, so the liquid can advance smoothly without creating bubbles or dry spots. In forward mode, the sample is driven in the same direction the medium is designed to transport it, so the blood encounters the capture or reaction zone in a clean, continuous path. Combining forward flow with a pre-wetting step ensures uniform wetting, reduces clogging, and improves reproducibility when using whole blood, even if only slight procedural adjustments are needed.

If you tried forward mode without any modification, the blood’s thickness could hinder consistent wetting and flow, leading to variability. If you used reverse mode, warming the sample might help a bit with viscosity, but the flow would proceed against the medium’s intended path, compromising contact with the reaction region. Doing reverse flow with pre-wetting still traps you in the less favorable flow direction, so the benefits of pre-wetting aren’t fully realized.