CPD: Casebook – food allergy and testing

In this case-based CPD module, consultant paediatric specialists in allergy Dr Thisanayagam Umasunthar and Dr Robert Boyle explain evidence-based approaches to food allergy in primary care, including accurate diagnosis of cow’s milk allergy, management of Pollen Food Syndrome, when testing is appropriate and identifying and managing anaphylaxis. Complete the full module on Pulse365 today.

Note that all cases in this module are hypothetical scenarios developed for illustrative purposes only

Learning objectives

This module will enhance your knowledge of the management of food allergy and testing, including:

• Accurately diagnosing cow’s milk allergy in infants and avoiding overdiagnosis.
• Recognising Pollen Food Syndrome triggers and managing symptoms appropriately.
• Understanding when and how to use allergy testing in food allergy cases.
• Identifying clinical features of a true anaphylactic reaction.
• Applying appropriate criteria for prescribing adrenaline auto-injectors.

Case 1. Mother requests testing for cow’s milk allergy for her formula-fed baby  

A young mother brings her 10-week-old bottle-fed baby to surgery stating that she wants him tested for cow’s milk protein allergy. She explains that the baby has various symptoms such as intermittent diarrhoea, being unsettled after feeds, rashes and occasional vomiting. The health visitor has suggested trying different milks but with no benefit.

1. What are the features of cow’s milk protein allergy?

Cow’s milk allergy is a food allergy that affects up to 1% of infants. There is a high level of milk allergy overdiagnosis in primary care in the UK and an increase in low-allergy formula prescribing without any other evidence for an increase in milk allergy.¹ Low-allergy prescription formulas contain glucose syrups that can contribute to childhood obesity and dental decay.^2,3 Much of the available education and clinical practice guidance in this area appears to promote overdiagnosis.^4,5

Cow’s milk allergy is usually a straightforward diagnosis, with symptoms that consistently occur after each exposure to cow’s milk protein (reproducible) and do not occur in its absence (specific).⁶  

Cow’s milk allergy can be immediate (IgE-mediated) when symptoms are much like any other immediate food allergy – with an urticarial rash, angioedema or vomiting within minutes of ingesting a food containing cow’s milk protein. Cow’s milk allergy can also be delayed (non-IgE mediated) when symptoms are mainly gastrointestinal. The most common form of non-IgE mediated milk allergy is Food Protein Induced Enterocolitis Syndrome, where infants vomit up to four hours after consuming cow’s milk protein. Typically, they vomit several times, seem quite unwell and then gradually recover over a few hours.

The clinical features in this 10-week-old infant of diarrhoea, unsettled behaviour, rashes and occasional vomiting are likely to be normal baby symptoms which will improve over time. There may be an element of ‘formula intolerance’ that could be improved by trying a different brand or product type. However, the lack of change in symptoms following the health visitor’s advice makes this less likely. Parents should be aware that the ‘comfort milks’ and other non-standard infant milks sometimes contain ingredients such as glucose syrups in place of lactose, so their use should always be limited where possible.

2. How can it be distinguished from other common problems in babies such as GORD or infant colic?

The key features of cow’s milk allergy are reproducibility and specificity of symptoms in relation to cow’s milk exposure. After the initial reaction, similar symptoms always occur with ingestion of sufficient amounts of cow’s milk protein (reproducibility). Symptoms do not occur without ingestion of cow’s milk protein (specificity).

Vomiting large volumes of milk after feeds affects about 20% of otherwise healthy infants and typically takes until the age of six to eight months to settle. This is gastro-oesophageal reflux and symptoms are most noticeable with large-volume feeds, milk that is more slowly digested, or physical forces from coughing, crying, tight clothes or lying down. Vomiting volume may reduce with addition of a feed thickener such as an alginate compound. However, constipation may be an adverse effect.

Vomiting as an allergic reaction to cow’s milk occurs only after cow’s milk ingestion and may be associated with a rash. Breastmilk or non-cow’s milk formula is tolerated without vomiting. Gastro-oesophageal reflux begins in the first days of life, as the baby begins to consume larger volumes of milk. Cow’s milk allergy most commonly begins in breastfed babies at several months of age, when dairy foods or cow’s milk formula are first introduced. Cow’s milk allergy can begin earlier in formula fed babies. For most types of cow’s milk allergy, a teaspoon (5ml) is sufficient to trigger symptoms. Infants with cow’s milk allergy who are regularly consuming cow’s milk formula usually become very unwell within days, with faltering growth, vomiting, diarrhoea and need for hospital attendance or admission.

Crying is common in this age group, with babies crying for an average of two hours per day in the first six weeks and one hour per day at 10 to 12 weeks.⁷ Crying or colic is not a typical sign of cow’s milk allergy. If the baby cries only after cow’s milk ingestion or always cries after cow’s milk ingestion and doesn’t cry after other types of feeding then they may have some hypersensitivity to cow’s milk formula.

Normal stool frequency in infancy can vary from many times per day to once every few days. The colour of stools can vary from yellow to brown to green. Stool frequency, stool colour and infant constipation are not signs of cow’s milk allergy. However, acute, explosive diarrhoea within hours of consuming cow’s milk formula, which doesn’t occur after other types of feeding, may indicate hypersensitivity to cow’s milk formula. Keep in mind the possibility of a post-viral lactose intolerance, which can also cause these symptoms.

Blood in the stools is quite common in young infants. Spots or streaks of blood and mucus in the stools of a young infant are usually caused by proctocolitis which is a self-limiting, transient condition that does not usually need specific intervention. Occasionally, in formula-fed infants, changing to a low-allergy formula can reduce the bleeding. However, the decision to make this change should be carefully considered, taking into account the self-limiting nature of proctocolitis and the potential health risks of using a glucose syrup based low-allergy formula.

Rashes are common during early infancy, and it can be difficult to distinguish seborrhoea from atopic eczema. Atopic eczema is very itchy, and should be treated with moisturisers or topical steroids; food is not the main cause of eczema, and dietary interventions should not usually be advised. Although NICE atopic eczema guidance highlights food allergens as potential eczema triggers in difficult cases, the use of dietary exclusions as a method for managing eczema is controversial and not supported by good evidence; whereas topical anti-inflammatory treatments work well for reducing eczema symptoms.⁸ We concur with the most recent international guideline which recommends against using dietary elimination to manage eczema.⁹ Eczema Care Online has a helpful toolkit for parents.

3. How can the diagnosis be confirmed? Do allergy tests have a role?

The most important component of cow’s milk allergy diagnosis is the clinical history. If symptoms are not both reproducible and specific, they are unlikely to be due to cow’s milk allergy. If an immediate (IgE-mediated) allergy is suspected, then blood specific IgE testing or skin prick testing can be done, but these carry a high false positive rate. Especially in the context of eczema, where total IgE antibody levels are high, blood specific IgE testing can lead to overdiagnosis of cow’s milk allergy.

If cow’s milk protein is excluded from an infant’s diet, for example via a trial of low-allergy formula, it is important to re-try cow’s milk protein as soon as symptoms have resolved, in order to confirm reproducibility. Prolonged use of a glucose syrup based low-allergy formula can potentially increase a child’s risk of early onset obesity and dental decay.^2,3

For most infants with suspected cow’s milk allergy, the diagnosis is one of the common symptoms of infancy listed above, and a cornerstone of management is reassurance that the symptoms are normal and will resolve over time.

Dr Thisanayagam Umasunthar is consultant paediatrician and Dr Robert Boyle is consultant paediatric allergist at Imperial College Healthcare NHS Trust, London

References

1. Li K, Wing O, Allen H et al. Time Trends, Regional Variation and Associations of Low-Allergy Formula Prescribing in England. Clin Exp Allergy 2024;54(11):909-918
2. Anderson C, Whaley S, and Goran M. Lactose-reduced infant formula with corn syrup solids and obesity risk among participants in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). Am J Clin Nutr 2022;116(4):1002-1009
3. Moynihan P. Update on the nomenclature of carbohydrates and their dental effects. J Dent 1998;26(3):209-18
4. Smith T, Townsend R, Hussain H et al. Milk allergy guidelines for infants in England promote over-diagnosis: A cross-sectional survey. Clin Exp Allergy 2022;52(1):188-191
5. Vincent R, MacNeill S, Marrs T et al. Frequency of guideline-defined cow’s milk allergy symptoms in infants: Secondary analysis of EAT trial data. Clin Exp Allergy 2022;52(1): 82-93
6. Allen H, Pendower U, Santer M et al. Detection and management of milk allergy: Delphi consensus study. Clin Exp Allergy 2022;52(7):848-858
7. Wolke D, Bilgin A, and Samara M. Systematic Review and Meta-Analysis: Fussing and Crying Durations and Prevalence of Colic in Infants. J Pediatr 2017;185:55-61.e4
8. Oykhman P, Dookie J, Al-Rammahy Y et al. Dietary elimination for the treatment of atopic dermatitis: A systematic review and meta-analysis. J Allergy Clin Immunol Pract 2022; 10(10):2657-66
9. AAAI/ACAAI JTF Atopic Dermatitis Guideline Panel; Chu D, Schneider L et al. Atopic dermatitis (eczema) guidelines: 2023 American Academy of Allergy, Asthma and Immunology/American College of Allergy, Asthma and Immunology Joint Task Force on Practice Parameters GRADE− and Institute of Medicine−based recommendations. Ann Allergy Asthma Immunol 2024;132(3):274-312