FPIES (Food Protein-Induced Enterocolitis Syndrome) is a unique and severe food allergy primarily affecting the gastrointestinal tract of infants and young children. Unlike common allergies driven by Immunoglobulin E (IgE) antibodies, FPIES is a non-IgE mediated condition. This means the body’s reaction is delayed and involves a different part of the immune system. This difference makes diagnosis particularly challenging, as there is no simple blood test to confirm its presence. A definitive diagnosis requires a specialized, methodical approach, starting with a careful review of the patient’s medical history.
Recognizing FPIES: Clinical History and Symptom Assessment
The initial step in diagnosing FPIES is obtaining a detailed clinical history of the patient’s reactions to food. Since symptoms can mimic a severe stomach virus, a clinician must carefully analyze the pattern of events to establish suspicion of FPIES. The characteristic presentation of acute FPIES is repetitive, profuse vomiting that typically begins one to four hours after ingesting the trigger food.
This delayed timing distinguishes it from immediate IgE-mediated reactions, which occur within minutes. The vomiting is often accompanied by signs of severe illness, including lethargy, pallor, and sometimes watery or bloody diarrhea hours later. Rapid fluid loss from severe episodes can lead to significant dehydration and hypotensive shock.
A careful history also helps distinguish acute from chronic FPIES, a less common form occurring when a trigger food is consumed regularly. Chronic FPIES usually affects infants consuming milk or soy formula, presenting with subtle, ongoing symptoms like intermittent vomiting, diarrhea, and poor weight gain. Clinicians must confirm that symptoms resolve when the suspected food is removed, establishing a clear link between ingestion and delayed gastrointestinal distress. A detailed food and symptom journal maintained by the caregiver is often invaluable for connecting delayed symptoms to a specific food protein.
Ruling Out Other Allergies: The Utility of Standard Tests
Allergists use traditional allergy tests to rule out more common, IgE-mediated food allergies that can present with similar symptoms. These standard tests include skin prick tests (SPT) and specific IgE blood tests, which measure IgE antibodies produced in response to a particular food protein. Since FPIES is a non-IgE mediated disorder, these tests are expected to be negative in most cases.
The primary utility of these tests is differential diagnosis, ensuring an immediate-type allergy is not the cause of the patient’s reaction. A positive IgE test to a suspected food in a patient with a delayed reaction suggests “atypical FPIES.” Patients with atypical FPIES show IgE sensitization alongside characteristic delayed gastrointestinal symptoms. This may indicate a higher risk of evolving into a classic IgE-mediated allergy over time.
Despite their limited role in confirming FPIES, performing these tests is a necessary step in the diagnostic pathway to accurately classify the patient’s condition. The absence of an IgE response, coupled with a suggestive clinical history, strongly supports the FPIES diagnosis. However, a negative IgE test alone is not sufficient to confirm FPIES, as it only confirms the absence of an immediate allergy.
The Gold Standard: The Medically Supervised Oral Food Challenge
The definitive method for confirming an FPIES diagnosis and identifying the specific trigger food is the Medically Supervised Oral Food Challenge (OFC). This procedure involves the controlled reintroduction of the suspected food to reproduce the characteristic FPIES reaction. Because of the potential for severe reactions, including dehydration and shock, the OFC must be conducted in a specialized medical environment with immediate access to emergency interventions.
The challenge is typically performed in an allergy clinic or hospital setting by trained personnel, including a physician and nurse. Before the procedure, the patient must be healthy and have completely avoided the suspected trigger food for a period of time. A peripheral intravenous (IV) line may be placed preemptively, especially for patients with a history of severe reactions, to allow for rapid administration of fluids and medications.
During the procedure, the patient is given the suspected food in a controlled, calculated dosage, often administered in three equal portions over an hour. The total amount of food protein administered is carefully measured, often ranging from 0.06 to 0.6 grams of protein per kilogram of body weight. After the final dose, the patient is closely observed for an extended period, typically a minimum of four hours, to capture the characteristic delayed onset of FPIES symptoms.
A positive result is confirmed if the patient exhibits classic FPIES symptoms, such as repetitive, profuse vomiting, during observation. If a reaction occurs, the challenge is immediately stopped, and the patient is treated with IV fluids to address dehydration and potentially with anti-vomiting medication like ondansetron. If the patient tolerates the challenge without symptoms, the food is considered safe and can be reintroduced into their regular diet.
Management and Treatment Principles
Once an FPIES diagnosis is confirmed, the primary management strategy is strict avoidance of the identified trigger food or foods. A nutritionist or allergist provides a personalized dietary plan to ensure the patient maintains adequate nutrition while adhering to the elimination diet. Infants reacting to cow’s milk or soy formula are often switched to a specialized hypoallergenic or amino-acid-based formula to support proper growth.
If accidental exposure occurs, acute treatment focuses on managing severe gastrointestinal symptoms. The mainstay of acute care is the administration of intravenous fluids to counteract the rapid dehydration caused by profuse vomiting and diarrhea. Ondansetron, an anti-emetic medication, may be used to help stop the vomiting.
For severe reactions involving lethargy, pallor, or hypotension, corticosteroid medications may be administered to dampen the inflammatory response. It is important to note that FPIES reactions do not involve the IgE pathway, meaning the standard emergency treatment for immediate allergies, epinephrine, is not effective for an FPIES attack. The long-term outlook is favorable, as most children outgrow the condition by age three or four. Resolution is confirmed by a repeat, medically supervised Oral Food Challenge to safely reintroduce the previously avoided food.