From the Guidelines
In a CBC and CMP, the most significant indicators of an allergic reaction are elevated eosinophils, typically above 500 cells/μL or greater than 6% of total white blood cells, and elevated total white blood cell count, which can occur due to the body's immune response to the allergen 1. When evaluating a patient for an allergic reaction, it is essential to consider the clinical presentation, including symptoms such as rash, respiratory distress, or hypotension, in conjunction with laboratory findings.
- Key laboratory findings that may indicate an allergic reaction include:
- Elevated eosinophils in the CBC, which is a key immune cell that responds to allergic stimuli
- Elevated total white blood cell count during acute allergic reactions
- Elevated liver enzymes (AST, ALT) if the allergic reaction affects the liver
- Altered electrolytes and renal function in severe systemic reactions
- Elevated glucose due to stress response or steroid administration According to the 2020 practice parameter update on anaphylaxis, the diagnosis of anaphylaxis is based on the presence of acute onset of symptoms, involvement of the skin or mucosal tissue, and either respiratory involvement or reduced blood pressure 1.
- The NIAID/FAAN diagnostic criteria for anaphylaxis include:
- Acute onset of illness with involvement of the skin, mucosal tissue, or both, with either respiratory involvement or reduced blood pressure
- Two or more of the following symptoms that occur rapidly after exposure to a likely allergen: skin-mucosal tissue involvement, respiratory involvement, reduced blood pressure, or gastrointestinal symptoms
- Reduced blood pressure as a result of exposure to a known allergen trigger It is crucial to note that these criteria should not replace clinical judgment, and epinephrine administration is not limited to patients meeting the diagnostic criteria 1. The most critical aspect of managing an allergic reaction is prompt recognition and treatment, and laboratory findings should be interpreted in the context of clinical symptoms to ensure timely and effective intervention 1.
From the Research
Allergic Reaction Indicators in CBC and CMP
- There are no specific indicators of an allergic reaction that can be seen in a Complete Blood Count (CBC) or Comprehensive Metabolic Panel (CMP) alone, as these tests are not typically used to diagnose allergic reactions 2, 3, 4, 5, 6.
- However, in the context of an allergic reaction, laboratory tests such as serum tryptase levels can be used to reflect mast cell degranulation, which can help clarify the diagnosis of anaphylaxis 4.
- The diagnosis of an allergic reaction is typically based on clinical presentation, medical history, and physical examination, rather than laboratory tests alone 2, 3, 4, 5, 6.
Laboratory Tests for Allergic Reactions
- Serum IgE-specific antibody testing or skin testing can be used to identify the allergen responsible for an immediate IgE-mediated response 2.
- Patch testing can be used to identify the allergen responsible for contact dermatitis 2.
- Serum tryptase levels can be used to reflect mast cell degranulation in the context of anaphylaxis 4.
Clinical Presentation of Allergic Reactions
- Symptoms of an allergic reaction can range from mild urticaria and swelling to abdominal cramping, respiratory collapse, and anaphylaxis 3.
- Anaphylaxis is a life-threatening systemic reaction that can cause airway, breathing, or circulatory compromise, and requires immediate treatment with intramuscular epinephrine 4, 5, 6.