New Skin Testing Protocol Helps Locate Isosulfan Blue Allergy

A new multi-step skin testing protocol effectively determines the presence of isosulfan blue allergy, according to a study conducted by researchers at the University of Virginia.

Monica G. Lawrence, MD, and her colleagues at the University of Virginia observed that although skin testing can be effective, currently there wasn’t a standardized protocol. So they decided to study 3 patients who displayed signs of perioperative anaphylaxis during sentinel lymph node biopsy with positive isosulfan blue exposure.

Isosulfan blue is a triphenylmethane dye utilized as an injection in sentinel lymph node biopsy procedures during breast cancer and melanoma surgeries. It essentially is used to measure the strength of the lymphatic system in some areas of the body. Anaphylaxis to isosulfan blue complicates 1-3% of sentinel lymph node biopsy procedures, creating an uncommon but clinically significant adverse event.

According to an e-mail correspondence between Lawrence and Reuters Health, “This skin testing protocol will allow clinicians to confirm if a patient is allergic to isosulfan blue dye so that it may be avoided in future procedures.”

Lawrence and her team successfully completed the procedure with one patient managed with diphenhydramine, commonly referred to as Benadryl. However, the remaining 2 patients required a more thorough treatment with epinephrine, prolonged intubation, and procedure delay.

Three to 4 weeks later, Lawrence and her researchers performed outpatient testing with the 3 patients involving a skin prick test (SPT) with a 1:10 dilution of isosulfan blue and full-strength isosulfan blue. The intradermal test (IDT) incorporated a 1:1,000 dilution of isosulfan blue, a 1:100 dilution of isosulfan blue, and a 1:10 dilution of isosulfan blue. The researchers interpreted each test result at 15 minutes.

According to the findings, none of the 3 patients suffered adverse test reactions. One had a positive IDT reaction to a 1:100 dilution, while the other 2 saw positive SPT reactions to the full-strength isosulfan blue.

Lawrence and her colleagues noted that these findings “suggest that this protocol has utility in a larger patient population and that up to 1:10 dilution of isosulfan blue is a nonirritating dose for the IDT.”

Naturally, extra precaution should be taken for safety measures. "In patients with positive skin testing reactions to isosulfan blue requiring an additional procedure involving dyes, care should be taken to avoid the cross-reactant patent blue dye and consider the alternative, methylene blue, which has not been associated with hypersensitivity reactions," Lawrence and her team concluded.