Perceptions when to mandate warmed transfusions in patients with cold antibodies vary widely. This is influenced by personal experience and sometimes plainly by the availability of technical heating devices. But with what temperature (T) does the blood really arrive at the patient"s arm? Finding no fitting publication of actual measurements in our quick literature search, we devised our own experimental setup.

Transfusion was simulated with expired red cell units, stored at T of 4-5°C and transfusion sets (Codan Med. Geräte GmbH, Ref 45.4424, 175 cm). T was recorded every minute in the blood bag (TESTO 110) and with a T probe (TESTO 440dP) using a hemodialysis Y-single needle adapter ((VMP/Effeemme Y-112), placed at the line"s end. A scale (Sartorius LC 12001P) helped to monitor flow speed, which was difficult to set. We measured T after resting 0-30" at RT 22-23°C and various "flow" timings (30-60").

Flow speed and time strongly influenced exit temperature. Directly from storage with flow time of 30" (average: 28,6", SD 2,5, min.: 24" max.: 31"), we had an average T(core) 14,6°C, min. 6,9°C, max 22,6°C and av. T(flow): 18,1°C, SD 1,78, min. 16,1°C max. 21,5°C. With 15" rest before 30" flow (av. 27,8" SD 2,23): Tcore 13,4°C min 8,2°C max 21,4°C Tline 18,1°C SD 1,13, min 16,1°C max 21,5°C. With 30" rest and 30" flow (av. 29" SD 0,82), Tcore 15,72°C, SD 2,51, min 12,6°C max 21,9°C. no rest and 60" flow (61,4" SD 7,5) Tcore 14,6°C min 6,9°C max. 22,6°C Tflow 21,6°C SD 0,9, min 18,7°C max 22,9°C. With rest 30" flow 60" (av. flow 54" SD 1,0): Tcore 16,7°C SD 2,9, min 12,5°C, max 22,6°C and Tflow 21,3°C SD 0,7, min 19,9°C max 22,7°C.

Blood bags were emptied via normal transfusion sets and T were recorded in standardized conditions. Directly from the refrigerator at the exit of the line the blood reached nearly room temperature when flowing slowly. This data helps avoiding unnecessary use of blood heating devices and may lower concerns regarding transfusion reactions.

Additionally, one practical hint resulted: It is better to transfuse slowly than waiting for the blood bag to acclimatize to room temperature.

No conflict of interests.