Gravity filtration of bovine, porcine and human blood on the

Retriever Medical is developing a disposable, gravity-fed filtration system intended to filter a person's own (autologous) whole blood before it is returned to them. Three chambers in a row each hold a removable filter: 2mm, 250 microns and 40 microns.

This early proof-of-concept study asked three questions: does the filter remove clot, does it damage red blood cells, and does it change how the blood clots?

• Clot removal: 30 cc of clotted bovine blood was mixed with saline in a 60 cc syringe, run through the filters by gravity, and the filtrate checked by eye for particles.
• Red cell integrity (porcine): 50 cc of pig blood was split into a 10 cc unfiltered and a 40 cc filtered sample. Both were tested for potassium, calcium and hematocrit and examined on blood smears.
• Red cell integrity (human): unfiltered and filtered human blood were tested tor LDH, AST, ALT, total bilirubin, albumın, potassium, hematocrit, platelet count and blood smear.
• Clotting: unfiltered and filtered human blood were tested for PT, PTT and INR.

The final filtrate had no visible thrombus or particles. In the pig blood, potassium, calcium and hematocrit did not differ between the unfiltered and filtered samples, and smears showed no change in red cell shape. In the human blood, smears showed no red cell or platelet injury, and most markers stayed the same.

Two values differed. LDH was higher in the filtered human sample (323 vs 171 U/L), and PTT was higher in the unfiltered samples (52 vs 31).  The authors note more blood samples need to be analyzed, and that further studies are needed on the safety of reinfusing blood filtered this way.