Younger brothers and sisters of peanut-allergic children are at higher risk for peanut sensitivity than children in general. However, a Canadian study published in the June 2016 issue of Allergy found that siblings whose peanut allergy tests were negative prior to introduction did not have an allergic response when they ate peanut for the first time.
The 154 siblings, who had never eaten peanut, ranged in age from under 12 months to over 5 years, with a median age of 23 months. Double-blinded skin prick tests were performed with peanut extract and peanut butter. Blood samples were collected for peanut-specific IgE analysis. Parents then fed peanut products to all the children under medical supervision.
Eight siblings experienced allergic reactions in response to peanut introduction. Of these, five needed to be given epinephrine. One child required two epinephrine injections and was later hospitalized. The eight reactive children all had either skin test reactivity to peanut or high concentrations of peanut-specific IgE antibodies prior to eating peanut (skin pricks with peanut extract did not elicit a response in one peanut-allergic child.)
The combination of negative skin-prick tests with peanut butter and negative serum levels of peanut-specific IgE had strong negative predictive value, meaning that the negative test results predicted the absence of peanut allergy at the time of peanut introduction. Overall 87 percent of siblings with negative skin and blood tests tolerated oral challenge with peanut. Six siblings tolerated peanut introduction but had weakly positive allergy tests. Another six siblings who did not test positive for peanut allergy experienced some symptoms after eating peanut products; however, these children tolerated a second peanut challenge and were later able to eat peanut. In total, about 90 percent of children with negative tests tolerated peanut exposure.
Peanut allergy is more common in younger siblings of peanut-allergic children, affecting 5.2 percent of the study cohort versus 1.7 percent of Canadian children. On average, the eight siblings who experienced allergic reactions to peanut were significantly older than the remainder of the cohort, with a median age of 4.1 years, compared to 1.9 years for participants who tolerated peanut on first or second challenge.
A survey of participating parents assessed their preferred approach to peanut introduction. Parents of peanut-allergic older children were very worried about introducing peanut at home without testing. Their anxiety scores averaged 8.4 on a 10-point scale, more than twice the anxiety level reported by parents whose older children did not have peanut allergy. For parents with allergic older children, peanut introduction provoked less anxiety if carried out at home after negative tests or if conducted under medical supervision without testing.
Despite indications that early peanut exposure may protect against peanut allergy, 15 percent of the parents whose younger children tolerated peanut did not feed them peanut at home, while 34 percent fed them peanut on a less-than-monthly basis. The principal reason cited was fear that the allergic sibling would be exposed to peanut accidentally. Parents who rarely or never provide peanut did not report significantly greater peanut introduction anxiety than parents who regularly feed peanut to their peanut-tolerant younger children.