Plasma preparation from whole blood using ultrasound

A technique to efficiently separate plasma from human whole blood is descri bed. Essentially, 3-mL samples are held on the axis of a tubular transducer and exposed for 5.7 min to an ultrasonic standing wave. The cells concentr ate into clumps at radial separations of half wavelength, The clumps grow i n size and sediment under gravity. A distinct plasma/cell interface forms a s the cells sediment. The volume of clarified plasma increases with time, T he separation efficiencies of transducers of 29-mm and 23-mm internal diame ters driven, by test equipment, at radial resonances of 3.4 and 1.5 MHz, re spectively, were compared. The average efficiency of separation was 99.6% a t 1.5 MHz and 99.4% with the 3.3-MHz system. The cleared plasma constituted 30% of the sample volume at 1.5 MHz and 25% at 3.4 MHz, There was no measu rable release of haemoglobin or potassium into the suspending phase, indica ting that there was no mechanical damage to cells at either frequency. A to tal of 114 samples from volunteers and patients mere subsequently clarified in a 1.5-MHz system driven by an integrated generator. The average efficie ncy of clarification of blood was 99.76% for the latter samples. The clarif ication achieved is a significant improvement on that previously reported ( 98.5%) for whole blood exposed to a planar ultrasonic standing wave field ( Peterson et al, 1986), We have, therefore, now achieved a six-fold reductio n of cells in plasma compared to previous results. (C) 2000 World Federatio n for Ultrasound in Medicine & Biology.