Healthcare items are one of the most important applications of traceability, since those items must be handled often in emergency conditions and the effects of errors could even be fatal. Among those items, the traceability of blood bags has drawn the greatest amount of attention, since these bags are prepared, stored, and used in different locations, and sometimes in different buildings or even handled by different organizations. The present leading traceability technology is the barcode, but its limitations are well-known. Barcodes require physical contact between the codes and the reader, or at least a very small distance, and good alignment between the two. Moreover, each barcode most be scanned individually. Therefore, a considerable manipulation of the items, or the reader, by an operator is required, and this slows down significantly the operations for large stocks of items [1
]. Furthermore, barcodes are subjected to mechanical stresses and external agents, so that they can be easily damaged. Moreover, blood bags must be complemented with a significant amount of extra information, such as the blood group or the harvest date, which cannot be handled by barcodes, because of the limited amount of information they can store. For these reasons, RFID technology [1
] is becoming the leading alternative, as it offers a number of significant advantages [1
]; however, to become fully effective, this technology needs a reorganization of the processes [6
]. A significant reduction in the reading time can be obtained, e.g., using a portal reader. Nevertheless, its location must be chosen taking into account both the blood movement and the electromagnetic environment. Moreover, these advantages can effectively be exploited only as long as the electromagnetic (EM) field of the RFID reader does not cause any adverse effects on the blood. It is well-known that a strong EM field can heat the blood. A large heating may even denature the blood, but for smaller temperature increase, some adverse effects can appear, such as the hemolysis of red cells and the modification of blood pH [7
], and render the blood useless. Therefore, every use of RFID in blood traceability must assure that no detectable heating occurs during the reading cycle. Despite its interest [3
], no standard rules exist at the moment about the use of RFID in blood bag traceability. Only a set of guidelines have been issued by the International Society of Blood Transfusion (ISBT). These guidelines strongly support the use of RFID in the HF band (i.e., at 13.56 MHz) for blood bags [8
]. The main reason leading ISBT toward this choice is the quasi-static nature of this field, which is not absorbed by the blood and therefore does not heat the blood itself Such claims are based on a Food and Drug Administration (FDA) evaluation of the effects of RF on blood cells [9
], done in 2008. The result of this evaluation was that no heating and no red cell or platelet damages occur during typical HF-RFID reading cycles, nor are higher fields or longer reading times used. However, HF-RFID advantages come together with some significant and intrinsic technical limitations, namely a reduced reading range and a low channel capacity, which lead to a long reading time. Moreover, multiple tag reading is possible, but not effective enough for the need of large collecting centers. Therefore, a comparison between HF-RFID and UHF-RFID is in order.
The presence of the ISO 18000-3 [12
] standard, which defines the specification of the RF interface, and the worldwide availability of the HF-RFID band can be important, but the other features of HF-RFID are quite easily matched by RFID in the UHF band. All the limitations of HF-RFID can be overcome by UHF-RFID [13
]; hence, this trade-off would be clearly in favor of UHF-RFID, as long as it does not cause detectable heating of the blood during a reading cycle. No systematic study on the effect of UHF electromagnetic fields on the blood has been performed. Only a few experimental data have been collected [14
] by exposing blood bags to the field of a portal reader for a time longer than a typical reading cycle. After all the exposures, no significant variation of the biological indexes (pH levels, platelet (PLT) count, and PLT aggregation rate) was found. The effect on the blood temperature has not been recorded. Therefore, the only data available have been obtained by a numerical simulation [15
]. However, the setups chosen in [15
], i.e., a few cylindrical tubes filled with blood plasma, exposed in a waveguide, or located in close proximity of a coil, are completely different from the actual reader field and bag shape, so the aim of this paper is to numerically evaluate the increase in temperature and the specific absorption rate (SAR) of a blood bag with a realistic shape, when exposed to a field very close to a typical UHF reader field, in order to assess, at least from this point of view, the use of UHF-RFID in blood bags traceability.