Strongly suspected allergy to cashew but a negative skin test to cashew - what to do?

A patient with urticaria and angioedema after eating cashews had a skin prick tests positive to almond and negative to cashew. How to explain it?

A negative food skin test is a good predictor of a negative food challenge, with greater than 95% certainty. However, one must have a "good quality" extract for skin test.

The incidence of "false-positive" skin tests to foods is much higher. The positive skin test to almond may not predict a clinical response, and may represent a sensitization without clinical reactivity.

Suggested approach:

- Specific IgE for cashew and almonds (sIgE)

- Prick-to-prick skin test using cashew nut (prick-puncture test). "Prick-to-prick" skin test testing with the fresh food in question can enhance the sensitivity of the skin test (AAAAI Ask the Expert, 2012).

- Get a fresh cashew extract and repeat the skin test

- See the container from which the cashew was taken to exclude cross-contamination with almonds, e.g. "made in a factory that also processes other tree nuts", etc.


8 top allergens account for 90 percent of food allergies. Specific IgE levels (sIgE) that predict the likelihood of passing an oral food challenge are shown in the figure. (click to enlarge the image).

References:

Acute urticaria after the ingestion of cashews with negative skin test to cashew. AAAAI Ask the Expert, 2011.

"Allergic to cashews, but thought it would be OK to eat almonds on AirFrance flight" - allergist on board saved his life http://goo.gl/P8Yh4