Alergi Susu Sapi

01Pathophysiology

Cow's milk allergy (CMA) is an adverse immune reaction to one or more proteins found in cow's milk, primarily casein (the heat-stable fraction, roughly 80% of milk protein) and whey proteins (alpha-lactalbumin, beta-lactoglobulin). It is the most common food allergy in the pediatric population, affecting approximately 2 to 3 percent of infants in the first year of life.

The pathophysiology diverges based on the immunologic mechanism involved. In IgE-mediated CMA, initial exposure to cow's milk protein sensitizes the infant's immune system, leading to production of allergen-bound IgE antibodies that coat mast cells and basophils. On re-exposure, cross-linking of surface IgE triggers immediate degranulation, releasing histamine, leukotrienes, and prostaglandins. This produces rapid-onset symptoms (within minutes to 2 hours): urticaria, angioedema, vomiting, wheezing, and in severe cases, anaphylaxis. This is the classic Type I hypersensitivity pathway.

In non-IgE-mediated CMA, the reaction is driven by T-cell activation and eosinophilic infiltration of the gastrointestinal mucosa. Because cell-mediated immunity is slower to develop, symptoms are delayed (hours to days after ingestion) and tend to be predominantly gastrointestinal: chronic diarrhea (often with blood and mucus), vomiting, abdominal pain, and failure to thrive. The inflammatory infiltrate damages the intestinal epithelium, leading to villous atrophy and impaired absorption, which explains the poor weight gain. The most recognized non-IgE entity in infants is food protein-induced allergic proctocolitis (FPIAP), where the hallmark is an otherwise well-appearing, thriving infant who passes streaks of blood and mucus in the stool.

A third group involves mixed IgE and non-IgE mechanisms, seen in conditions like eosinophilic esophagitis (EoE) and atopic dermatitis aggravated by cow's milk protein. Here, both immediate and delayed pathways contribute, producing a clinical picture that overlaps with pure IgE-mediated and pure cell-mediated disease.

The critical clinical link is this: the type of immune mechanism determines the timing, organ involvement, and severity of presentation. IgE-mediated disease is fast, often cutaneous or respiratory, and carries anaphylaxis risk. Non-IgE-mediated disease is slow, predominantly gastrointestinal, and generally does not cause anaphylaxis but leads to chronic nutritional compromise if untreated.

02Classification and Clinical Manifestation

FPIAP = Food protein-induced allergic proctocolitis; FPIES = Food protein-induced enterocolitis syndrome; FPE = Food protein-induced enteropathy; EoE = Eosinophilic esophagitis.

03Diagnostic Workup

The diagnostic approach depends on whether you suspect IgE-mediated or non-IgE-mediated disease. For IgE-mediated CMA, the best initial test is a skin prick test (SPT) or serum cow's milk protein IgE. A positive SPT (wheal >= 3 mm above the negative control) or elevated serum IgE indicates sensitization but does not by itself confirm clinical allergy. Many sensitized patients tolerate cow's milk without symptoms. That distinction is critical on exam questions: sensitization does not equal allergy. The test tells you the immune system recognizes the protein; the oral food challenge tells you the body reacts clinically.

For non-IgE-mediated CMA (FPIAP, FPIES, FPE), IgE-based tests are characteristically negative. The diagnosis rests on a clinical triad: (1) compatible symptoms, (2) resolution on elimination diet, and (3) recurrence on reintroduction. The elimination diet typically lasts 2 to 4 weeks. In breastfed infants, the mother eliminates all dairy from her own diet; in formula-fed infants, the child is switched to an extensively hydrolyzed formula.

The most accurate (confirmatory) test for both IgE-mediated and non-IgE-mediated CMA is the supervised oral food challenge (OFC). This is performed in a controlled setting, with the allergen given in graduated doses under observation. A positive challenge (symptom recurrence) confirms the diagnosis. In practice, OFC is often deferred if the clinical picture and elimination response are convincing, but for exam purposes, remember it as the gold standard.

Stool studies showing occult blood and eosinophils support a diagnosis of allergic proctocolitis but are nondiagnostic. Endoscopy with biopsy is reserved for cases where eosinophilic esophagitis is suspected (>= 15 eosinophils per high-power field on esophageal biopsy) or when the clinical course is atypical and other enteropathies (such as celiac disease) must be excluded.

04Management and Treatment

The cornerstone of CMA management is strict avoidance of cow's milk protein. This sounds straightforward, but in practice it requires careful label reading, as cow's milk derivatives (casein, whey, lactalbumin) appear in many processed foods.

For breastfed infants, the mother should eliminate all dairy products from her diet. Breast milk remains the preferred feeding source. The mother needs calcium supplementation (1000 mg/day) and vitamin D (600 IU/day) to offset the dietary restriction. Symptoms in the infant typically improve within 2 to 4 weeks of maternal elimination. If they do not, consider incomplete maternal avoidance, a concurrent soy protein allergy (which co-occurs in up to 10 to 15 percent of CMA infants), or an alternative diagnosis.

For formula-fed infants with mild to moderate disease, the first-line switch is to an extensively hydrolyzed casein-based formula (eHF), such as Nutramigen or Alimentum. These formulas break down the protein into small peptides that are less likely to trigger an immune response. Approximately 90 to 95 percent of infants with CMA tolerate eHF. Do not use partially hydrolyzed formulas (e.g., Enfamil Gentlease), as these retain enough intact protein to provoke reactions. If symptoms persist despite eHF for 2 to 4 weeks, the next step is an amino acid-based formula (AAF) such as EleCare or Neocate, where proteins are broken down completely into free amino acids. AAF is also the first-line choice for severe CMA and FPIES, bypassing eHF altogether.

Soy-based formulas are generally not recommended as first-line alternatives in infants under 6 months because of the high rate of cross-reactivity (10 to 14 percent of CMA infants also react to soy protein) and concerns about phytoestrogen exposure in young infants. In older infants (over 6 months) with confirmed IgE-mediated CMA and documented soy tolerance, soy formula may be considered.

For acute anaphylaxis in IgE-mediated CMA, the treatment is intramuscular epinephrine at a dose of 0.01 mg/kg (using 1:1000 concentration), with a maximum of 0.3 mg per dose in children. The injection goes into the mid-outer thigh. The dose can be repeated every 5 to 15 minutes. All families of children with IgE-mediated CMA should have an epinephrine auto-injector prescribed and be trained in its use.

For an acute FPIES episode, the presentation can be dramatic: profuse vomiting, pallor, lethargy, and even hypovolemic shock. The immediate treatment is IV fluid resuscitation with normal saline at 20 mL/kg. Ondansetron (0.15 mg/kg IV, maximum 16 mg) has been shown to abort acute FPIES episodes effectively and is now a standard part of acute FPIES management. Epinephrine is not effective for FPIES because the mechanism is not IgE-mediated.

Most children with CMA develop clinical tolerance by age 3 to 5 years. IgE-mediated CMA tends to persist longer than non-IgE-mediated forms. Periodic re-evaluation with supervised oral food challenges is recommended every 6 to 12 months to assess whether the child has outgrown the allergy.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap on exam questions about cow's milk allergy is confusing it with lactose intolerance. These are fundamentally different conditions. CMA is an immune-mediated reaction to the protein in cow's milk. Lactose intolerance is a non-immune, enzymatic deficiency affecting carbohydrate digestion. A vignette describing a 4-month-old with bloody stools, eczema, and vomiting after formula introduction is CMA, not lactose intolerance. Primary lactose intolerance is exceedingly rare before age 3 and essentially does not present with bloody stools or systemic allergic features. If you see an infant with bloody stools and the answer choices include both, the presence of blood in the stool should immediately point you toward CMA.

Another common pitfall is choosing a partially hydrolyzed formula as the correct management. Partially hydrolyzed formulas (such as Enfamil Gentlease) still contain enough intact cow's milk protein to provoke symptoms and are not therapeutic for CMA. The correct answer is an extensively hydrolyzed formula, escalating to an amino acid-based formula if there is no improvement.

Watch for the FPIES vignette: a young infant brought to the emergency department with profuse vomiting, lethargy, and hypotension 1 to 4 hours after feeding. This can look like sepsis on first glance, and many students incorrectly choose empiric antibiotics as the next best step. The key discriminator is the temporal link to feeding and the absence of fever or infectious source. The correct initial management for an acute FPIES episode is IV fluids and ondansetron, not antibiotics.

Finally, remember that a positive skin prick test or serum IgE alone does not confirm CMA. Sensitization is not the same as clinical allergy. The gold standard is the oral food challenge. If a vignette gives you a child with a positive IgE to cow's milk but no symptoms on ingestion, that child is sensitized, not allergic, and does not require avoidance.

The core competency being tested across CMA questions is the ability to distinguish immune-mediated food allergy from non-immune intolerances, to match the clinical subtype (IgE-mediated vs. non-IgE-mediated) to the correct diagnostic and therapeutic pathway, and to avoid defaulting to inappropriate formulas or misidentifying FPIES as sepsis.