| Summary: | We aimed to identify any detrimental effects on platelet quality and clinical effectiveness, of irradiated platelets compared to non-irradiated platelets for transfusion. The review was conducted in accordance with PRISMA guidelines. The protocol was prospectively registered on PROSPERO [CRD42023441930]. Our search identified 3002 references, of which we included 44 studies. Forty-one were in vitro only studies, two studies were in healthy volunteers, and one study reported clinical outcomes in thrombocytopenic patients. X-ray was used exclusively in three studies, and alongside gamma irradiation in one study. Two studies did not report the source of irradiation. The remaining 38 studies used gamma irradiation only. We assessed risk of bias (ROB) for studies reporting clinical and in vivo outcomes using ROB 2.0 (3 studies). We adapted a ROB tool designed for animal studies to assess ROB for the studies reporting in vitro outcomes (43 studies). We assessed the certainty of the evidence for the eight outcomes deemed most important to assess platelet quality and clinical effectiveness (where day 0 is the day of the blood draw).<br><br>
• High certainty of a small decrease in pH (day 7) with irradiation: mean difference (MD) 0.04 lower (95% CI, −0.07 to −0.00).<br>
• Moderate certainty of an increase in P-selectin (day 5) with irradiation: MD 1.58 % higher (95% CI, 0.72-2.45).<br>
• Moderate certainty of no difference in supernatant glucose (days 5 and 7) and P-selectin (day 7).<br>
• Very low certainty of any difference in pH (day 5), post-transfusion bleeding risk (WHO 2+), and post-transfusion platelet survival time.<br>
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Overall, gamma irradiation has little to no effect on most markers of platelet quality and effectiveness. Where there is evidence of detriment from irradiation, differences are small in vitro, and are unlikely to affect clinical outcomes following transfusion. However, the evidence base is limited. Only half the studies could be included in any analysis. There is very limited evidence for x-ray as a source of irradiation and, given the potential benefits of using x-ray over gamma irradiation (ease of use and safety requirements), we would welcome further research comparing x-ray to gamma, and x-ray to a non-irradiated control.
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