1. Presented by Ahmad Kohsar, DO, MS and reviewed by Lorraine Blagg, MA, MLS(ASCP)^CMSBB, AHI(AMT)

A patient with an unknown medical history was found obtunded and unresponsive and was admitted to the ICU. They were found to be anemic with a hemoglobin of 6.5 g/dL. They were transfused a unit of RBCs. During the transfusion of the red cells, they spiked to a temperature up to 38.9°C from a baseline of 37.5°C. Additionally, they had persistent hypoxia with O₂ saturation in the high 80s, requiring supplemental oxygen. Recent imaging just before transfusion shows a unilateral consolidation possibly from aspiration, and they appeared euvolemic with normal pressures and normal BNP. The results of the transfusion reaction workup are as follows:

Blood Bank HistoryPatient ABO/Rh: A POS
Antibody Detection: Negative
Requirements: Leukoreduced RBCs
Transfused RBCs: A POS

Blood Product RequisitionDemographic information matched
Special Requirements: Leukoreduced
Patient Location: ICU

Patient’s ABO/Rh: A POS
Blood Component Type: RBCs
Blood Component ABO/Rh: A POS
The blood component is crossmatch-compatible

Patient Plasma Hemolysis Check: Negative
Observation of Transfusion Line for Hemolysis: Negative

Blood Component ABO/Rh:

Anti -A	Anti-B	Anti-D
4+	0	4+

Pre-Sample DAT:

Polyspecific IAT (Anti-IgG and Anti-C3)	Check Cells
0	2+

Pre-Sample ABO/Rh:Front Type:

Anti -A	Anti-B	Anti-D	Monoclonal Control
4+	0	4+	0

Reverse Type:

A1 cells	B cells
0	4+

Pre-Sample Antibody Detection: LISS

	37 C	IAT	CC
Screening Cell I	0	0	2+
Screening Cell II	0	0	2+

37: Incubation at 37C
IAT: Indirect Globulin Test (Anti-IgG)
CC: Check Cells

Pre-Sample Crossmatch: LISS

RBCs	37C	IAT	CC
Transfused Unit	0	0	2+

Post-Sample DAT:

Polyspecific IAT (Anti-IgG and Anti-C3)	Check Cells
0	2+

Post-Sample ABO/Rh:Front Type:

Anti -A	Anti-B	Anti-D	Monoclonal Control
4+	0	4+	0

Reverse Type:

A1 cells	B cells
0	4+

Post-Sample Antibody Detection: LISS

	37 C	IAT	CC
Screening Cell I	0	0	2+
Screening Cell II	0	0	2+

Post-Sample Crossmatch: LISS

RBCs	37C	IAT	CC
Transfused Unit	0	0	2+

Preliminary gram stain and cultures have been negative to date.

Question: What is the most likely cause of these findings?