BACKGROUND AND OBJECTIVES: Transfusion reaction is often masked in critically ill patients because of underlying disease or certain pre-medications. The study was planned to know the incidence and determine risk factors associated with these acute transfusion reactions (ATRs) in intensive care (ICU) patients by actively monitoring the transfusion events. MATERIAL AND METHODS: In this prospective observational study, critically ill patients admitted to ICU and having an ICU stay of 24 h prior to transfusion were enrolled. Each enrolled patient was actively monitored after each transfusion of blood component at 15 min, 1 h, 6 h and 24 h. Transfusion reactions reported from ICU during the study period were considered as passively reported ATRs. RESULTS: Transfusion of 850 components translating to 430 transfusion episodes was actively monitored. Thirty-three ATRs were observed in 27 patients. Incidence of ATR on active monitoring (0.039) was higher than on passive reporting (0.006). On active monitoring, 06 cases of TACO, 2 cases of TAD, 1 case each of TRALI and TTBI, 3 cases of FNHTR were recorded. A significant association between positive fluid balance (p = 0.01) and generalised oedema (p = 0.01) was observed with TACO. Twelve cases were labelled as unclassifiable complication of transfusion. Rise in BP was the only symptom observed in all these cases. The mean post-transfusion systolic blood pressure and diastolic blood pressure at 1 h, 6 h and 24 h were significantly higher (p <
0.05) than pre-transfusion values. CONCLUSION: Active monitoring provides us with a true insight into the incidence of various ATRs.