[Quality of platelet products: current methods of in vitro assessment]

[Platelet-leukocyte aggregates as a marker for platelet activation in platelet concentrates]

OBJECTIVES

Several in vitro laboratory tests to assess the quality control of platelet concentrates (PC) are available. Some of them have a good correlation with the platelet recovery index. To assess the quality control of standard PC prepared in our blood bank, we measured the blood gas and the degree of platelet activation.

MATERIALS AND METHODS

SPC were prepared by the PRP method. Fifty-five SPC (45 SPC at day one of storage and 20 SPC at day five of storage) were analysed. Blood gas (pH, PO(2), PCO(2) and bicarbonate concentration) in the SPC were measured by blood gas automate. Platelet activation profile were determined by measuring the percentage of platelet expressing the CD62p (% CD62) and the percentage of platelet-leukocyte aggregate (% PLA).

RESULTS

The pH values of all studied SPC were comprised between 7.0 and 7.6. SPC at day 1 of storage have a significantly higher pH than those at day 5 of storage (7.5+/-0.05 versus 7.3+/-0.14; p<0.001). The % CD62p were higher in SPC at day five compared to the SCP at day one without reaching a statistical significance (28.4+/-15% versus 24.3+/-9.7%, p=0.052). The percentage of PLA were higher in SPC at day one compared to SCP at day five although this difference is not statistically significant (22.2+/-7.5% versus 17.9+/-8.0%; p=0.23).

CONCLUSION

Preparation and storage procedure adopted in our centre did not significantly affect the quality SPC. Our study is the first to assess the PLA in PC. Studies assessing the PLA are warranted to appreciate the clinical impact of this parameter.

[Platelet-washing solution optimization]

Different washing and homogénéisation solutions are hereby analysed by comparing the evolution of functional indicators during the preservation of washed aphaeresis platelet concentrates: physiological pH 4.5 and 6 solutions, buffered physiological pH 6.8 glucose solution, and two physiological pH 7 citrate solutions with acetate. Prior acidification of platelet concentrates proved to be essential. Two washings with manual or automated technique, guarantee residual proteins at a level of less than 0.5 g. Solutions T-Sol Baxter or SSP Macopharma allow us to obtain a product that meet the PSL specifications. Routine since June 2004, washings are done with a physiological pH 6 solution, then homogeneised with T-Sol solution. Platelet recovery, swirling phenomenon, lack of agrgegates, pH maintenance, low increase in the platelet average volume and maintenance of intra-cell potassium level, suggest that platelet entirety is preserved beyond the product's expiration date. The platelet transfusion yield of these products is satisfactory.

[New automatic test for the study of platelet response to variations in osmotic pressure: application in the evaluation of the viability of platelet concentrates]

Studying the osmotic resistance or swelling of platelets has often been suggested as a global test to assess the viability of those cells. A number of authors have also analysed the behaviour of platelets in hypotonic media by a variety of complementary methods (cell count, morphology, determinations of substances released, photometric measurement of aggregation induced by aggregating agents, etc). Most studies are currently based on the so-called "osmotic shock response" test, which measures according to time the light transmitted through platelet-rich plasma (PRP) after dilution in distilled water. In this study, the authors describe a new automated and reproducible test using slow dialysis to assess platelet osmotic resistance. The "Fragilimeter", a device initially described by the authors to characterise RBC fragility, has been adapted to the study of platelet osmotic behaviour. The variations in light transmission through a platelet suspension according to NaCl concentration are linked to the change in cellular volume and lysis and characterise the viability of the cells. The results obtained with normal platelets revealed the good reproducibility of the technique. The osmotic resistance is evaluated for two parameters: anticoagulant (citrate, EDTA) and cellular concentration. The test was applied to quality control of stored platelet concentrates for transfusion, prepared with different cell separators.

[Comparative validation of manual and automated methods for mixing and volume control of total blood samples]

During blood collection, agitation and volume limitations are critical to ensure thorough mixing of the blood with the anticoagulant and obtention of the predetermined volume. These 2 factors are essential to prevent blood activation and to obtain well standardized blood products. The objective of this study was to compare the quality of the blood collected using 2 types of collection method: tripping of a scale at a predetermined volume limit of 450 mL in the presence of manual agitation, and the 3 blood collection monitors currently available in France. A minimum of 100 collection procedures was performed for each of the 4 methods tested. Results were found to be equivalent using either the manual or the automated procedures with regard to both the accuracy and reproducibility of the blood volumes obtained and the collection times and flow rates. The characteristics of the red blood cell concentrates, platelet concentrates and plasma units prepared from the first 30 collections of each group were assessed and compared to regulatory requirements. The quality of all these products was found to be comparable to that currently observed at quality control and no product was rejected at the release control for reasons of poor collection. An assessment of the practicability of the different methods showed that the automated devices are subject to practical difficulties involving transport and battery loading. In addition, the cost of this equipment is approximately 5 times higher than that of the scales. In conclusion, the results of this study show that in our hands, no significant advantage could be expected from the use of automated blood collection monitors as compared to simple scales with manual mixing. These results further raise the question of the applicability to labile blood products of the comparative validations currently accepted in the pharmaceutical industry, in order to allow the use of correctly validated alternative methods.