Introductions: ATR is the most common adverse event associated with transfusion reactions. This study aims to determine the differences in DLC and CRP levels in pre- and post-blood transfusion, with and without ATR. Methods: A prospective cohort study involving 92 patients at Wahidin Sudirohusodo Hospital from September 2024 to June 2025, consisting of major ATR (24 patients), minor ATR (20 patients), and without ATR (48 patients) based on the CDC NHSN Hemovigilance 2025 diagnostic criteria. DLC and CRP tests were performed pre- and post-blood transfusion. Statistical analysis was performed on characteristics, comparisons, and correlation tests. Results: Major and minor ATR events occur more frequently in TC blood products (p<0.05). Mayor ATR events decreased basophil and monocyte percentages (p<0.05). Minor ATR events increased neutrophil percentage, accompanied by a decrease in lymphocyte count and percentage (p<0.05). Without ATR events decreased in WBC and monocyte count (p<0.05). Mayor and minor ATR events increased delta WBC, delta neutrophil count and percent, accompanied by a decrease in delta lymphocyte percent (p<0.05). Conversely, without ATR events decreased delta WBC, delta neutrophil count and percent, accompanied by an increase in delta lymphocyte percent (p<0.05). Positive correlation between delta WBC with delta neutrophil count (r=0.923; p<0.05), delta neutrophil percent (r=0.504; p<0.05), and negative correlation between delta lymphocyte percent (r= 0.455; p<0.05). Conclusions: Delta WBC, delta neutrophil count and percent, and delta lymphocyte percent post-ATR event can be used as additional tests to complement the ATR diagnostic criteria.