High volume of polysorbate-containing (Tween 80) solutions induces false-positive results in intradermal test.

Background: Intradermal test is used to detect causative allergens in IgE-mediated hypersensitivity. The surfactant polysorbate 80 can be added to intradermal test solutions to more reliably dissolve the allergen and ensure a constant bioavailability of the injected allergen. Polysorbate 80 has, however, some histamine-releasing properties which could blur the difference to the histamine-induced wheal. Routinely serving as a control.

Objective: Allergen-free polysorbate 80 containing (0.005%) test solutions were therefore systematically tested at different injection volumes to see whether polysorbate can falsify skin reactions and if yes whether conditions can be identified to avoid this.

Methods: In a partly blinded study, 30 patients were tested intracutaneously at the back: each received at three separate sites 0.05 mL of polysorbate-containing solvent, 0.02 mL polysorbate-containing solvent as well as 0.02 mL polysorbate-free solvent. After 15 min, wheal and erythema were documented and planimetrically quantified.

Results: Unexpectedly 23 of 30 (77%) patients showed false-positive test reactions to the volume of 0.05 mL of the polysorbate-containing solvent whereas the polysorbate-containing solvent with 0.02 mL and the polysorbate-free solvent with 0.02 mL injection volume had no reinforcing effect on skin test reaction.

Conclusions: Different volumes of polysorbate-containing solutions, all recommended by manufacturers for intradermal tests, may significantly influence test results. The study shows that a polysorbate 80 used at 0.005% in solvents for intradermal test to provide a better bioavailability of allergens produces false-positive reactivity in a surprising and a hitherto unknown 77% if the 0.05 mL volume is injected. It is, therefore, mandatory to strictly adhere to an intradermal test volume of 0.02 mL as only then falsifying effects of the polysorbate additive are avoided, and comparable test results are ensured.