Optimal conditions for white cell reduction in red cells by filtration at the patient's bedside

Background: A quality control program of white cell (WBC) reduction in red cells at the bedside was implemented, based on postfiltration counting in a Nageotte chamber of the residual WBCs from samples taken from a segment of the transfusion set, after 1-in-10 sample dilution with Turks's solution. During a 1-year quality control program, 5.1 percent of counted units had apparent filtration failures, that is, WBC counts exceeding 5 × 10⁶ per unit. The cause(s) for these apparent failures were investigated. Study Design and Methods: In Study 1, residual WBCs from 150 buffy coat-free red cells filtered through one type of filter at 4°C, 20 to 24°C, or 27°C in 5 to 10 minutes, 50 to 100 minutes, or 100 to 200 minutes were counted as described above. In Study 2, residual WBCs in samples collected from segments of the transfusion set and from the postfiltration bags were counted in parallel by a new, more sensitive counting method. In this method, 5 mL of filtered red cells was diluted with 20 mL of 3-percent paraformaldehyde and centrifuged, the pellet was resuspended to 500 μL with a lysis solution, and the WBCs were counted in a Nageotte chamber. In Study 3, residual WBCs were counted by the 3-percent paraformaldehyde method in samples from postfiltration bags of 1- to 2- day-old buffy coat-rich red cell units filtered through a second type of filter. Filtration was started within 30 minutes of the removal of the unit from the refrigerator, ambient temperature was 20 to 24°C, and the median filtration time was 90 minutes per unit. results: Study 1: Median WBC counts per unit increased progressively from 51,000 at 4°C to 934,000 at 27°C, with intermediate values at 20 to 24°C. In no unit did the WBC count exceed 5 × 10⁶ if filtration at 20 to 24°C was completed within 100 minutes, while counts in excess of 50 × 10⁶ were found at 20 to 24°C and at 27°C with filtration times of 100 to 200 minutes, and 50 to 100 minutes, respectively. Study 2: The relation between segment and postfiltration bag WBC counts obtained by the 3- percent paraformaldehyde method was poor, with the latter being almost always lower than the former. Study 3: None of the 120 units filtered through the second type of filter at 20 to 24°C in 50 to 100 minutes contained more than 3.2 × 10⁶ WBCs; the median value was 147,000 WBCs per unit. Conclusion: On the basis of the results with the 3-percent paraformaldehyde method, which showed the unreliability of segment counts, a new policy was adopted for quality control of bedside WBC reduction, based on controlling the time of and temperature at transfusion. Bedside WBC reduction in 1- to 2-day-old red cells performed with the second type of filter at 20 to 24°C in less than 100 minutes per unit allowed the preparation of units that meet the standard of fewer than 5 × 10⁶ WBCs in all tested cases. Bedside WBC reduction with the second type of filter and under the controlled conditions reported seems effective.