Comparison of methods for the evaluation of microaggregate removal by blood transfusion filters 1

Abstract

Two promising methods of assessing the removal of blood microaggregates or other particulates from stored blood by microfilters, namely electronic particle size distribution analysis and screen filtration pressure (SFP) measurements, were compared. Microaggregate counts and size distributions have been difficult to quantitate because of a lack of reproducibility of the measurements. This problem has now been largely eliminated by the use of a red cell lysing solution containing hexadecyltrimethyl-ammonium bromide (CTAB), acetic acid and glutaraldehyde which permits destruction of the red cells yet stabilizes the microaggregate counts. As a consequence it has been possible to make a quantitative comparison with the screen filtration pressure method. The correlation between the SFP values obtained with screens having pore sizes of 20 × 20, 30 × 30, and 40 × 40 μ and the number of microaggregates measured electronically has been examined for outdated blood bank blood. The 30 μ screen was found to offer advantages over the 20 and 40 μm screens. Samples containing different relative concentrations of microaggregates were prepared by mixing various proportions of repeatedly filtered and unfiltered blood such that the maximum SFP was ⩽ 450 mm Hg using the 30 μ screen. When SFPs > 250 mm Hg were extrapolated from the straight line trace between ∼ 20 to 250 mm Hg, it was shown that the SFP values were linearly related to the relative quantity of filtrable material. A linear relationship was also observed between the relative quantity of microaggregates and the particles counted electronically. The simplicity and reproducibility of the SFP procedure offer advantages over electronic particle size distribution analysis for the evaluation of the performance of blood microfilters.