Triple apheresis platelet concentrate quality after pneumatic tube system, conveyor box, and courier transport: An observational study

Abstract Background and Aims Platelets are prone to activation from handling; they are therefore transported as gently as possible, most commonly by courier. Speedier methods like pneumatic tube system (PTS) transport could improve patient care but may subject platelets to mechanical stress. To test the impact of mechanical stress caused by transport, we compared a PTS with a conveyor box and courier transport on apheresis platelet function. Methods Fourteen apheresis platelet concentrate triple donations were analyzed by light transmission aggregometry (LTA), rotational thrombelastometry (ROTEM), and flow cytometry before and after indoor transport over 800 m by PTS, conveyor, and courier, respectively, while recording shocks and vibrations with a high‐frequency acceleration data logger. Shock index scores were calculated as shock intensity (g‐force) times frequency. Results The shock index was 81 for courier, 6279 for conveyor, and 9075 for PTS. Flow cytometry revealed no significant difference in platelet surface expression of CD62p before (16%) and after transport via courier (15%), conveyor (14%), or PTS (16%). LTA with adenosine phosphate and thrombin receptor‐activating peptide‐6 resulted in comparable platelet aggregation for courier, conveyor, and PTS. ROTEM assays showed no relevant differences in coagulation time, clot formation time, and maximum clot firmness between transport modes. Conclusion Though the mechanical challenge was smallest with courier transport, there were no significant differences in platelet activation or aggregation between the three transport modes. These data contradict restrictions on the use of PTSs for platelet concentrate transport.


| INTRODUCTION
Platelets are fragile blood cells and may be activated upon mechanical stress. 1 Activation is accompanied by shape change followed by dense and alpha granule secretion, P-selectin (CD62p) expression, phosphatidylserine exposure, and finally membrane blebbing and microparticle formation. [2][3][4] Platelet concentrates are important therapeutics in transfusion medicine to prevent or treat bleeding in patients with low platelet count or poor platelet function. Due to their fragile nature, platelets are stored in blood donation bags after collection under gentle agitation to prevent sedimentation and activation. 5,6 Taking careful handling into account, platelet concentrates are usually transported to the patient by courier or conveyor systems. Although several studies indicate that pneumatic tube system (PTS) transport does not result in a loss of platelet quality, most of them were carried out with whole blood and buffy coat-derived concentrates instead of apheresis platelet concentrates. [7][8][9][10] However, considering the operating mode of PTS with its transport by air pressure, the pneumatic cushioning could prevent the cells from mechanical stress and could be appropriate for a soft and quick transport.
Therefore, this three-arm study was designed to comparatively evaluate the impact of three different transport modes-PTS, conveyer system, and manual transport-on platelet quality and thus focused on functional tests of apheresis platelet concentrates by accelerometry, aggregometry, thrombelastography, and flow cytometry 11,12 while taking the shock load into account.

| Apheresis platelet collection
The study included 14 participants (all male) with a minimum platelet count of 300 × 10 9 /L in peripheral blood who donated triple platelet concentrates in autologous plasma via the Trima

| Transport
The first bag of each triple donation was sent by conveyor, the second by PTS, and the third by courier over a distance equivalent to 800 m. Each transport container was equipped with a high-frequency acceleration data logger (MSR 165; MSR Electronics). All transports and tests were performed on the same day. The conveyor (Siemens system type SimaCom VT; Telelift GmbH) is a rail transport system with special transport boxes for light freight; it transported the platelet concentrates at walking speed (0.5 m/s) and covered the transport distance in 30 min. 14 The PTS (Sumetzberger) transported the products in cylindrical capsules by compressed air at a speed of 3 m/s and covered the transport distance in 4 min. 15 Manual transport by courier took about 8 min.

| Accelerometry
During transport, an acceleration data logger (MSR 165; MSR Electronics) measured shocks and vibrations over time (shock load) at a frequency of 800 Hz with a three-axis acceleration sensor. Raw data were converted to.csv files and analyzed with R. G-force measurements for each transport mode are shown in Figure 1. Based on acceleration along the X, Y, and Z axes, the acceleration vector sum (A sum ) of a time series was calculated as the square root of the sum of acceleration along each axis squared ( Ax ² + A y ² + A z ²) to express the shock load. Shock index scores were calculated as the shock intensity (g-force) times frequency of shocks greater than the predetermined threshold of 2 g (force). The cut-off value of 2 g was chosen in such a way that, on the one hand, the noise of small vibrations was not taken into account, and on the other hand, it was chosen so low that as many shocks as possible could still be taken into account. This was assumed at 2 g but is based on assumptions.

| Light transmission aggregometry (LTA)
LTA was performed for measurement of platelet aggregation 20 min after transport. Briefly, 300 μl samples from the transported platelet units were diluted with 300 μl physiological saline (NaCl; B. Braun).

| Thromboelastography
Thromboelastography of each triple (3-unit) donation was performed before and about 2 h after transport using the rotational thrombelastometry (ROTEM) INTEM and EXTEM assays and software version 2.6.3 (all Tem Innovations GmbH) as described previously. 16

| Ph analysis
The pH was measured undiluted on the blood gas analyzer ABL 90 Flex (Radiometer) as per the manufacturer's instructions.
F I G U R E 1 Exemplary analysis of shock intensity (g-force) and frequency values associated with the three transport modes: (A) manual, (B) conveyor system, and (C) pneumatic tube system (PTS).

| Statistical analysis
Microsoft Excel 2010, IBM SPSS Statistics (version 25), and R (version 3.6.3) with its library pracma were used to collect data, generate box plots, and to determine median, mean, and standard deviation values.
Normal distribution was tested with Shapiro−Wilk. Data are presented as median and range. In addition, the 95% confidence interval (CI) of the mean value was given for all data. We performed the Levene test on the assumption of variance homogeneity and a two-sided t test for independent samples. p values below 0.05 were considered statistically significant.

| RESULTS
Fourteen triple donations yielded a total of 42 units with a median volume of 249 ml and a maximum content of 8 × 10 11 platelets per apheresis ( Table 1). The maximum apheresis time was 120 min per apheresis platelet concentrate triple donation, consisting of three units each. Additionally, samples removed from each donation before transport were used as controls (n = 14).
The shock load index was 81 for courier, 6279 for conveyor, and 9075 for PTS ( Figure 3). Thus, the PTS was associated with the highest dynamic mechanical load and manual transport with the lowest, while that for conveyor transport was in the same range as PTS.
ROTEM analysis yielded the following median clotting time, clot formation time, and maximum clot firmness values in the EXTEM test (activation of clotting by thromboplastin) for the three transport modes studied versus before transport (exemplary thrombelastogram, see Figure 4): 95%, 100%, and 101% for manual transport, 94%, 101%, and 100% for conveyor system, and 99%, 99%, and 99% for PTS, respectively. In the INTEM test (activation of coagulation via the contact phase), median clotting time, clot formation time, and maximum clot firmness values were 101%, 102%, and 99% for manual transport, 95%, 96%, and 100% for conveyor transport, and 105%, 104%, and 99% for PTS, respectively, compared to before transport. No transport mode resulted in a significant loss of quality, as indicated by these parameters, except for the conveyor system in EXTEM measurement for clotting time LTA with ADP, AA (ASPI test), and TRAP-6 showed light transmission before versus after transport of 99%, 107%, and 103% for manual transport, 96%, 104%, and 98% for transport via conveyor, and 93%, 103%, and 106% via PTS ( Figure 5). There was no significant loss of quality in manual, conveyor, or PTS. The only exception was in measurements using arachidonic acid as the agonist, where all three transport methods resulted in an at least partially significant change in ASPI values compared to baseline: PTS with p = 0.05 (95% CI: 100% −115%), conveyer with p = 0.05 (95% CI: 100%−117%) and courier with p < 0.05 (95% CI: 101%−118%). Since courier transport also resulted in a significant difference, these results could be considered comparable.

| DISCUSSION
Platelet concentrates are indispensable for persons requiring platelet support, especially hematology, oncology, and surgery patients. Fast but gentle transport to the patient is essential for preserving platelet quality. The aim of our study was the evaluation of a safe transport F I G U R E 2 Exemplary plot (A) and overlay histogram (B) of CD62p expression from unstimulated (blue) and TRAP-6-stimulated (green) platelets with the mean fluorescence intensity (MFI) shift after stimulation.
mode. Therefore, we examined the impact of PTS, conveyor, and manual transport on platelets. The comparability of pooled and apheresis platelet concentrates is a much-debated topic. 6 To avoid an influence of donor variability as well as of storage, 11 we used apheresis platelet concentrates on the day of donation. The strength of this study was that each concentrate presented its own control as each of it was split into three equal parts. Compared to conveyor transport, PTS was much faster and caused no significant loss of platelet concentrate quality, although associated with the highest dynamic mechanical load. However, the data logger recordings confirmed that manual transport subjects platelets to the lowest dynamic mechanical load. In this study, we applied LTA, flow cytometry, and thromboelastography and received information about platelet activation and coagulation. It would be of further interest to study platelet adhesion conducted by automated flow chamber systems which could give the opportunity to simulate platelet activity T A B L E 1 Characteristics of the study population and platelet concentrates before transport. under physiological blood flow conditions. 17,18 This aspect was not part of our examination and limits the information given.
PTS is a popular and widely used means of transporting platelets in hospitals. Compared to manual transport, both PTS and conveyor ensure a rapid supply of patients with blood preservation and additionally save personnel by decreasing time-consuming manual transport. However, the PTS could be susceptible to mechanical failure, defects, overuse, and abuse. 19 Rapid acceleration and deceleration resulting in shear stress could affect platelet activation and aggregation. 20,21 Several studies considered platelet quality after pneumatic tube transport. Sandgren et al. 22 reported the effects of transport on the quality of buffy coat platelet concentrates and figured out that it had no  In addition, the shock load also plays a decisive role and must be considered when evaluating the influence of transport on platelet quality. Thus, all transport containers used in our study were equipped with acceleration data loggers, because, for example, the higher the acceleration, the higher the influence on the ROTEM parameters. 30 In particular, using a three-axis accelerometer offers the opportunity to record a combination of acceleration, magnitude of force, and duration of the transport. 31

ACKNOWLEDGMENT
The authors would like to thank the team of the Institute for Clinical Chemistry and Laboratory Medicine and the Department for Anesthesiology, University Hospital Regensburg for their help, support, and handling of the whole apheresis process.

CONFLICTS OF INTEREST
The authors declare no conflicts of interest.

TRANSPARENCY STATEMENT
The corresponding author Viola Hähnel affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.

DATA AVAILABILITY STATEMENT
The authors confirm that the data supporting the findings of this study are available within this article.