Assessment of fluorescence interference in the basophil activation test: a case of indocyanine green-induced anaphylaxis.

Indocyanine green (ICG) is increasingly used for fluorescence-guided surgery and can rarely cause perioperative anaphylaxis. The basophil activation test (BAT) is a safe in vitro tool for identifying culprit drugs, but its flow-cytometric readout could theoretically be confounded by the intrinsic near-infrared fluorescence of dyes such as ICG, and this potential interference has not been systematically examined. We describe a patient who developed intraoperative anaphylactic shock after ICG injection and assessed whether its intrinsic fluorescence confounds the BAT. In the patient, BAT showed a clear concentration-dependent increase in CD203c expression, supporting ICG as the culprit. Two complementary observations suggested that ICG fluorescence did not substantially confound the assay: whole-blood samples containing ICG without antibodies produced no detectable signal in the PE channel, and BAT in three control subjects who tolerated ICG showed no activation except a nonspecific increase at the highest concentration. As a proof of concept, this approach may help apply BAT to ICG and, potentially, to other fluorescent or chromogenic drugs.