A 28-year-old man (B Rh-positive) undergoes elective open-heart surgery and receives 6 units of B Rh-positive packed RBCs intraoperatively. On postoperative day 2, he develops jaundice, dark urine, and a hemoglobin drop from 10 g/dL to 6.5 g/dL. Reticulocyte count is 8.5%, total bilirubin 4.2 mg/dL (direct 1.8 mg/dL), and LDH 680 U/L. Direct antiglobulin test (DAT/Coombs) is strongly positive. Blood bank reports that the transfused blood was correctly typed and cross-matched. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis **Key Point:** The timing (postoperative day 2), positive DAT, and hemolysis pattern point to a **delayed hemolytic transfusion reaction (DHTR)**, not an acute reaction. The blood was correctly typed and cross-matched, excluding ABO incompatibility. ## Distinguishing Acute vs. Delayed Hemolytic Transfusion Reaction | Feature | Acute HTR | Delayed HTR | |---------|-----------|-------------| | **Onset** | Minutes to hours during/immediately after transfusion | 24 hours to 14 days post-transfusion | | **Mechanism** | Pre-existing antibodies (ABO, major incompatibility) | Alloimmunization to minor antigens (Kidd, Duffy, MNS) from prior transfusions | | **DAT result** | Positive (IgG or IgM coating RBCs) | Positive (IgG coating RBCs) | | **Hemoglobin drop** | Rapid, severe (often > 2 g/dL in minutes) | Gradual over 24–72 hours | | **Bilirubin** | Mild elevation initially | Elevated (conjugated > unconjugated) | | **Cross-match** | Incompatible | Compatible (antibody was not detected at transfusion) | | **Fever, chills, flank pain** | Prominent | Mild or absent | ## Why This Case Is DHTR 1. **Timing:** Jaundice and hemolysis on postoperative day 2 — classic 24–72 hour window 2. **Positive DAT:** Indicates IgG antibodies coating transfused RBCs 3. **Compatible cross-match:** Blood was correctly typed, meaning no major incompatibility detected pre-transfusion 4. **Hemoglobin drop:** Gradual decline from 10 to 6.5 g/dL over 24 hours (not acute collapse) 5. **Elevated LDH and bilirubin:** Consistent with extravascular hemolysis **High-Yield:** DHTR occurs in patients previously sensitized to minor blood group antigens (Kidd, Duffy, MNS, Kell) who have received prior transfusions or pregnancy. The initial transfusion at surgery re-exposed the patient to the antigen, triggering an anamnestic (memory) response. ## Management 1. Stop transfusion immediately 2. Verify patient and blood unit identity 3. Repeat DAT, blood smear, reticulocyte count, LDH, bilirubin 4. Check urine for hemoglobinuria 5. Supportive care: hydration, monitor for acute kidney injury 6. Transfuse only if Hb < 5 g/dL and symptomatic; use antigen-negative blood if possible 7. Identify the offending antibody for future transfusions **Clinical Pearl:** DHTR is usually self-limited and milder than acute HTR because hemolysis is predominantly extravascular (spleen) rather than intravascular. Mortality is rare (~1%) unless complicated by renal failure.