Clinical relevance of the venom-specific immunoglobulin G antibody level during immunotherapy.

Parameters associated with successful venom immunotherapy in insect allergy were sought by comparison of treatment failures with successes. Half-dose treatment was completely protective in 32 patients (successes) but was only partially effective in eight (failures). The outcome of treatment was not related to the severity of pretreatment sting reactions, to the degree of skin-test sensitivity, to an atopic personal history, or to age or gender. The mean yellow jacket venom-specific IgG antibody level (by the Staph-A solid-phase radioimmunoassay) was significantly less in the failures (3.9 +/- 0.6 microgram/ml) than in the successes (7.3 +/- 1.1 microgram/ml) (p less than 0.01). When the failures were successfully treated, their mean IgG level (6.1 +/- 1.3 microgram/ml) was significantly greater than that associated with treatment failure (p less than 0.025). Patients with an IgG antibody level above 5.0 microgram/ml were significantly more likely to be fully protected (p less than 0.02). Those whose IgG levels were less than 5 microgram/ml had a risk of reaction similar to that in untreated patients. We conclude that early in the maintenance phase of low-dose venom immunotherapy, the risk of a reaction to a challenge sting is significantly greater for those patients with low levels of venom-specific IgG antibodies.