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What methods are used to measure the pH of donor platelets when doing routine QC activity required by the 23rd edition of AABB Standards (5.7.5.16 and 5.7.5.19)? |
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A colleague wonders what methods are used to measure pH of donor platelets when doing routine QC activity required by the 23rd edition of AABB Standards (5.7.5.16 and 5.7.5.19)? For reference, AABB Standard 5.7.5.16 requires that validation and quality control of Platelets from whole blood shall demonstrate that at least 90% of units sampled contain ≥ 5.5 x 1010 platelets and have a pH ≥ 6.2 at the end of allowable storage. AABB Standard 5.7.5.19 requires that validation and quality control of Platelets Pheresis shall demonstrate that at least 90% of units sampled contain ≥ 3.0 x 1011 platelets and have a pH ≥ 6.2 at the end of allowable storage. FDA criteria [21 CFR 640.24(d)] apply. The following comments have been received. 1. Two blood centers in Los Angeles report that they check platelet product pH using pH meters. One uses a Beckman Coulter pH meter that is calibrated daily with calibrators at pH 4, 10 and 7. They also run two levels of QC daily - the QC buffers have a pH of 4 and 7, and are provided by a commercial supplier other than the supplier of the calibrators. The other blood center in Los Angeles reports that they use an Orion 320 PerpHecT® Basic Benchtop pH Meter along with purchased buffer solutions. Equipment maintenance and calibration is per the manufacturer's instructions. 2. A blood center in a sunshine state reports that they use a Corning pH pen. QC is performed each day of use by testing with buffer solutions of known pH at 6, 7 and 8. The pen is calibrated upon receipt and at any time the reading deviates more than + 0.2. 3. A colleague reports that a blood center in Maryland uses a Corning Check-Mite pH meter that is calibrated daily using solutions with known values of '4' and '7' respectively. 4. A blood center in the Midwest reports that they use a Corning pH meter 430, which is calibrated daily with pH 7 and pH 10 buffers and 'checked' with a pH 8 buffer. If the platelet unit's pH is below 7.0, the pH meter is calibrated with pH 4 and pH 7 buffers and checked with a pH 6 buffer. The calibrators/controls are buffers that are purchased from a commercial supplier. 5. A hospital based donor collection program in North Carolina reports that they determine platelet product pH on blood gas machines. 6. A hospital based donor collection program in New Hampshire reports that they measure platelet product pH with a blood gas instrument that undergoes QC sufficient for patient results. They prefer a closed system approach to pH determination to prevent spurious results due to CO2 shifts. 7. Editor's Note: Other pH meters (list not intended to be exhaustive) are described at the following links:
ADDENDA May 29, 2006 8. A colleague in Amsterdam recommends that pH measurements of platelet products should be done using a closed system (like in a blood gas analyzer). If an open system is used, carbon dioxide (CO2) can rapidly leave the solution, leading to an increase in pH (10 mm Hg decrease of pCO2 results in 0.2 pH units increase). Speed of CO2 going out of solution depends on the starting value of pCO2, but this can happen very rapidly at the pCO2 values normally found in platelet concentrates in plasma (50 - 70 mm Hg). The method of sampling also influences final results. In his opinion, the best way to sample the product is by a syringe, and with immediate measurement after taking the sample. |
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Please submit comments to the e-Network Forum. Ira A. Shulman, MD |
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Posted: May 21, 2006
Addenda: May 29, 2006 |
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