Both serum IgE (Immunoglobin E) level and blood Absolute Eosinophil Count (AEC) are useful tests in evaluating and diagnosing allergies, but they serve different purposes and have their own strengths and limitations. So, they are often measured together in clinical practice. While IgE and eosinophils are both associated with allergic responses, they do not always change in tandem. It is possible for a person to have high levels of IgE but a normal AEC, or vice versa. This is because allergic reactions are complex and involve multiple components of the immune system, and the specific immune response can vary depending on the type and severity of the allergic condition.
IgE is an immunoglobulin that plays a key role in allergic reactions. When a person is expose to an allergen, such as pollen or dust mites, IgE levels in the blood may rise as the immune system mounts an allergic response. High levels of IgE in the blood are often seen in people with allergies, asthma, and other allergic conditions.
Eosinophils are a type of white blood cell that are involved in allergic responses and can be elevated in certain allergic and inflammatory conditions. Eosinophils are known to play a role in defending against parasitic infections, but they are also implicated in other allergic conditions such as eosinophilic asthma, eosinophilic esophagitis, and allergic rhinitis.
In many cases, there may be a correlation between serum IgE level and AEC. For example, in conditions such as allergic asthma or allergic rhinitis, both serum IgE level and AEC may be elevated. This is because eosinophils are often recruited to sites of allergic inflammation in response to IgE-mediated immune responses.
In some cases, a person may have elevated IgE levels without an accompanying increase in eosinophils, or vice versa. A person may have high IgE levels with a normal AEC if their allergic response is mediated by other types of immune cells, such as mast cells or basophils, rather than eosinophils. Conversely, a person may have an elevated AEC without a significant increase in IgE levels if their allergic response is not primarily mediated by IgE. So, there may not be a strong correlation between serum IgE level and AEC in non-allergic conditions such as certain types of infections (eg parasitic infestations), autoimmune diseases and some types of cancers.
Eosinophilia without significantly elevated IgE can occur in a variety of conditions, including:
- Eosinophilic disorders eg. eosinophilic asthma, eosinophilic esophagitis, eosinophilic gastroenteritis, and hypereosinophilic syndrome.
- Some parasitic infections, such as helminth infections (e.g., roundworms, hookworms).
- Certain inflammatory or autoimmune conditions, such as vasculitis, allergic granulomatosis (e.g., Churg-Strauss syndrome), and some connective tissue disorders.
- Some drug reactions can cause eosinophilia, and these reactions may not always involve IgE-mediated allergic responses.
A condition in which a person has a high serum IgE level but a normal absolute eosinophil count (AEC) is less common, but it can occur in certain situations. For example;
- Some case of Atopic dermatitis
- Allergic bronchopulmonary aspergillosis (ABPA)
- Hyper-IgE syndrome, also known as Job syndrome.
- In some cases, individuals may have elevated IgE levels due to other factors such as genetic predisposition, without an associated increase in eosinophils.
Therefore, while there is a relationship between serum IgE level and AEC, it is not always a direct correlation, and other factors (like clinical presentation, medical history, and other diagnostic findings) should be considered when interpreting these laboratory values. Your doctor will be the best person to advise you on the interpretation of these test results and any necessary follow-up testing or treatment.
Dr Prashant Goyal