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Last Updated
3rd o November, 2011
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There is often great confusion regarding cow’s milk allergy (CMA) and Lactose Intolerance, with the terms often used interchangeably despite both being separate disorders and very distinct.
Food allergies such as cow’s milk allergy are a form of food intolerance that involves the immune system. Lactose intolerance describes a form of food intolerance caused by deficiency of a specific enzyme and does not involve the immune system. See 'Lactose Intolerance'
Cow’s milk allergy is caused by an abnormal immune response to harmless milk proteins and generally results in the rapid appearance of symptoms after consumption of cow’s milk.
Despite some similarities between the proteins found in human and bovine milks, cow’s milk proteins can still be recognised as “foreign” by the human immune system.
In the majority of individuals the immune system recognises these proteins as harmless and tolerates them in the body, however in CMA individuals, the immune system becomes sensitised and reacts to the proteins by mounting a damaging inflammatory response.
Of the 8 most prevalent food allergies, cow’s milk allergy is the most common amongst infants. It usually develops early in infancy when susceptibility is highest and soon after exposure to cow’s milk infant formula. Onset after 12 months is rare and the risk of developing CMA is reduced by exclusive breastfeeding, but this may not prevent the risk altogether.
Types of cows milk allergy:
Cow’s milk allergy (CMA) is often divided into cow’s milk protein allergy (CMPA) where there is clear evidence of involvement of the immune system and cow’s milk protein intolerance (CMPI) where there is no involvement of the immune system.
Allergies to milk are broadly classified and commonly referred to as “immediate hypersensitivity” as the onset of symptoms occurs within minutes to an hour following exposure to the allergen (in this case protein) and “delayed” with the onset of symptoms occurring from 1 hour to several days after ingestion of milk; hence it is often called a “delayed hypersensitivity”.
Diagnosis
Diagnosis of cow’s milk allergy is difficult due to the wide range of possible symptoms that may occur. It is important that reliable techniques are used to diagnose CMA in order to avoid unnecessary exclusion of cow’s milk from the diet.
The generally accepted methods of diagnosing CMA include:
Skin tests: this involves using either a test lancet or needle, which is first pricked in the food and immediately afterwards in the skin. The value of this test is limited since it measures only IgE mediated reactions and thus will yield negative results in patients with non-IgE mediated responses. Patch tests measure non-IgE responses and may be of some value in patients with skin problems resulting from the handling of a particular food.
The RAST (radioallergosorbent) test: This is the best known laboratory test used for detecting circulating IgE antibodies. It requires the binding of the allergen onto an “allergosorbent” such as a cellulose paper disc or a plastic surface. The allergosorbent is incubated with a sample of the patient’s blood serum, which allows any IgE or IgG antibodies present to bind to it. This is then washed to remove any unbound antibody, after which it is incubated with isotopically labelled anti IgE antibody. After several washings, the radioactivity bound to the allergosorbent is measured. Using this measurement and a standard reference curve, the amount of allergosorbent-bound IgE present can be estimated. RAST tests have a number of limitations, for example, they are expensive, can give false positive results, cannot identify individual food triggers in non-IgE mediated food intolerances and a patient with a history of reactions to a food, such as a type of nut, cannot be assessed for intolerance to related foods such as other nuts.
Elimination diet: All suspect foods are eliminated for approximately 2 weeks prior to dietary challenge. If symptoms disappear during the elimination period, suspect foods are added to the diet, one by one, in small amounts; but increasing the dose daily until normal portion size is achieved. This is usually conducted under medical supervision.
Food challenges: very small amounts of the suspect food are given orally and then symptoms are observed. This test should only be performed under medical supervision where medical facilities are available.
The prognosis of CMA is good, with remission rates of about 45-50% at 1 year of age, 60-75% at 2 years and 85-90% at 3 years. This means 9 out of 10 sufferers will grow out of the allergy by the age of 3. The allergy is most likely to persist in those with a strong family history of allergy especially other food allergies such as to eggs, soya, peanuts or citrus fruits.
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