Rationale | Challenges are usually performed to elicit tolerance to an age-appropriate quantity of pasteurised cow's milk or formula—for example, 120–200 ml (age depending). There are, however, many other reasons as for undertaking a cow's milk challenge |
Indications | Most allergy centres seek to achieve a 50% negative challenge outcome rate. The clinician needs to estimate this risk through considering one or more of the following variables: previous reaction severity, tolerance of extensively heated milk, concomitant asthma, age of the child and allergy test results (these may include one or more of specific IgE, IgE component tests, SPT to milk extract and fresh milk) |
Setting | It is difficult to predict for the likely severity of future milk-induced allergic reactions. The majority of challenges can safely be performed in a Day Ward setting. If the challenge is considered “high risk”, then a high care setting should be available with access to a PICU. Home challenges may safely be performed for non-IgE-mediated milk allergy outcomes, but only in the absence of evidence of an IgE-mediated milk allergy. If eczema is to be used as an outcome, then the patient may need to attend at set intervals for the standardised assessment thereof |
Design | An “open” unblinded challenge is usually adequate for a certain diagnosis (particularly if the outcome is negative ie, tolerance). A double-blinded placebo-controlled food challenge (DBPCFC) is occasionally required to establish an unequivocal diagnosis of allergy. In order to minimise false positive results, research study designs need to make use of DBPCFC's. There are many possible variations to a challenge design; these include food used, number of incremental doses, intervals between doses, dose quantities, use and type of placebos. Challenges performed for the investigation of non-IgE-mediated allergies may include designs that make use of elimination and re-introduction diets |
Safety | Supervised milk challenge in a controlled medical setting have an excellent safety record with no fatalities reported. Nonetheless, safety is increased by following basic challenge principles: |
patients should avoid medicines that may mask symptoms or indeed prevent the treatment of symptoms before undergoing the challenge | |
resuscitation skills and equipment should be to hand | |
a detailed clinical examination, to ensure the patient is well and free from active asthma, is mandatory before commencing | |
any existing “rashes” should be clearly identified in order that confusion does not arise once the challenge has commenced | |
use a low starting dose as most reactions occur early on in a challenge as do most severe allergic reactions | |
challenges performed for the diagnosis of cow's milk-induced FPIES should be performed with a cannula in situ and facilities for ongoing supervision in the event of significant and prolonged dehydration | |
Follow-up postchallenge | A clear emergency and dietary plan, based on the challenge outcome, needs to be generated and communicated to the patient/family and healthcare practitioners. Appropriate emergency medications should be made available. Follow-up, usually by telephone, some 24 h postchallenge is ideal, as delayed symptoms are not uncommon—for example, eczema exacerbations |
FPIES, food protein-induced enterocolitis syndrome; SPT, skin prick testing.