Understanding Lab Tests for Eczema: What to Expect

Eczema is a chronic inflammatory skin condition characterized by dry, itchy, and inflamed patches of skin that are prone to infection. Affecting up to 30% of children and 10% of adults worldwide, most cases of eczema are diagnosed clinically, relying on a combination of visual examination and medical history. In primary care settings, routine laboratory testing is not typically required for diagnosis or initial treatment. 

However, laboratory tests can provide valuable insights into underlying causes and triggers for individuals with persistent, severe, or treatment-resistant eczema. This article explores the potential benefits of lab tests in managing eczema, helping patients and healthcare providers better understand which tests to consider and how they can inform more effective, personalized treatment strategies.

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When Are Lab Tests for Eczema Necessary?

While medical history and a thorough visual examination are paramount in diagnosing and managing eczema, laboratory tests can become necessary in certain situations to better understand the condition's underlying factors. Further investigation is warranted in cases where the disease is persistent, severe, or unresponsive to standard treatments. For example, if a patient's eczema does not improve with first-line therapies like topical corticosteroids or moisturizers, a doctor may recommend lab tests to uncover hidden triggers or underlying causes.

Eczema is considered part of the "atopic triad," which refers to a group of related conditions that commonly occur together: eczema, asthma, and allergic rhinitis (hay fever). This connection highlights the role of allergies in eczema development. Many individuals with eczema have heightened immune responses to environmental and dietary allergens. These allergens can trigger or worsen eczema flare-ups. As a result, allergy testing may be recommended to identify specific triggers, allowing for better management and avoidance strategies to reduce eczema symptoms.

Patients with atopic dermatitis (the most common type of eczema) are at an increased risk of recurrent skin infections, most often caused by the bacterium Staphylococcus aureus. However, viral and fungal infections can also occur concomitantly. If left untreated, an infection can spread systemically, so prompt testing when there is concern for infection is important.

Autoimmune conditions, such as psoriasis, cutaneous lupus, and mixed connective tissue disease (MCTD), can be misdiagnosed as eczema. Studies have also shown that atopic dermatitis is associated with some autoimmune diseases, such as Crohn's disease, ulcerative colitis, celiac disease, and vitiligo. Various tests can be ordered to help differentiate between these diseases and identify comorbid conditions contributing to disease severity.

Common Lab Tests for Eczema

Let's discuss some of the most common laboratory tests considered for diagnosing and managing eczema: 

Allergy Testing (IgE Tests)

Immunoglobulin E (IgE) is an antibody the immune system produces in response to perceived allergens. Elevated serum IgE levels are common in patients with eczema, reflecting the body's hypersensitivity to allergens, including dust mites, pet dander, pollen, mold, and certain foods. 

There are two main types of allergy testing for eczema:

1. Skin Prick Test: In this test, small amounts of potential allergens are introduced just under the skin's surface, typically on the forearm or back. If a person is allergic, a small raised bump (wheal) will appear within 15-20 minutes, indicating an immediate allergic reaction. This test helps identify environmental or dietary allergens that may trigger eczema flare-ups. The test provides quick results but can be uncomfortable and comes with a small risk of anaphylaxis. (32) 
2. Blood Tests: These blood tests measure the levels of specific IgE antibodies directed against certain allergens. Blood tests are often preferred over skin prick tests for individuals with severe eczema, who may have damaged or sensitive skin, or for those unable to discontinue antihistamines. Compared to skin prick testing, results can take longer and may be less sensitive for detecting certain allergens. (32)  

Patch Testing for Contact Dermatitis

Contact dermatitis is a subtype of eczema that occurs when the skin reacts to direct contact with an allergen or irritant. It is characterized by red, itchy, and inflamed skin, often accompanied by blisters, scaling, or dry patches. Unlike other forms of eczema, contact dermatitis is triggered explicitly by substances that come into contact with the skin.

Patch testing is used to identify delayed allergic reactions that cause contact dermatitis. Unlike skin prick tests, which assess immediate allergies, patch tests evaluate how the skin reacts to potential allergens over time. Small samples of allergens are applied to patches and affixed to the patient's back or arm. These patches are worn for 48 hours, after which they are removed, and a healthcare provider evaluates the skin. A second evaluation occurs within another week to check for delayed reactions.

Because so many irritants and allergens can cause contact dermatitis, your doctor will begin with a standard allergen panel, including nickel, fragrances, and preservatives, which can identify about 70% of responsible allergens. If initial testing is inconclusive, your doctor may do additional testing with an expanded panel that finds about 80% of allergens. (6, 34) 

Skin Biopsy

According to the National Eczema Association, a physical examination of the skin is usually sufficient to diagnose eczema. However, in some cases, your dermatologist may perform a skin biopsy to rule out other skin conditions that can present similarly. Examples include: 

• Zinc deficiency
• Seborrheic dermatitiss
• Cutaneous T-cell lymphoma
• Scabies
• HIV-associated dermatitis

A skin biopsy is an in-office procedure performed by a dermatologist or other qualified healthcare provider to remove a small skin sample that will be examined under a microscope. 

Common histopathological findings consistent with atopic dermatitis include: 

• Acanthosis: thickening of the skin
• Espongiosis: fluid buildup in the skin's epidermal layer
• Parakeratosis: retention of nuclei in the cells in the stratum corneum layer of skin 
• Infiltration of white blood cells, especially lymphocytes, mast cells, and eosinophils
• IgE deposits

Microbial Tests for Infection

A skin culture with antibiotic susceptibility testing is indicated if:

• There is clinical suspicion of a skin infection
• The patient experiences recurrent skin infections
• Skin infections do not respond to antibiotic therapy

Staph. aureus is isolated on culture from 90% of adults with atopic dermatitis. Other pathogens of concern include: 

• Bacterial Infections: Methicillin-resistant Staph. aureus (MRSA)
• Fungal Infections: Candida and dermatophytes
• Viral Infections: herpes simplex virus (HSV)

Blood Tests for Inflammation Markers

While these tests may not be recommended in standard-of-care medical guidelines, you could request that inflammatory markers be included on an evaluatory laboratory panel for eczema. 

Eczema is a systemic inflammatory disease that manifests as a breakdown of skin barrier function, skin sensitization, and hyperreactivity to allergens and irritants. Therefore, tackling inflammation is key to treating eczema, especially in moderate-to-severe cases. (13) 

Blood tests like erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) assess the level of inflammation in the body. While these tests are not specific to eczema, they can quantify the degree of inflammation and severity of the condition (39). 

Understanding Lab Test Results

Typical lab results to expect in patients with eczema include:

• Elevated serum IgE levels
• Positive allergy (blood, prick, and patch) tests 
• Staph. aureus skin colonization
• Elevated inflammatory markers

The results provide valuable insight into the potential causes or exacerbating factors of a patient's eczema. Consulting with a dermatologist, allergist, or other healthcare provider to review results helps patients understand their results within the broader context of their medical history, symptoms, and response to treatment.

How Lab Tests Influence Eczema Treatment Plans

By aligning test results with an individual's specific eczema profile, healthcare providers can offer more precise and effective long-term management strategies, including targeted allergen avoidance and tailored medication recommendations.

Nearly 40% of children with moderate-to-severe atopic dermatitis have IgE-mediated food allergies, though the specific allergens vary widely within this group. Allergy panels identify individual food triggers, allowing for targeted elimination diets that remove problematic foods without being overly restrictive.

Similarly, positive results for environmental allergens like dust mites, pet dander, or pollen can lead to tailored advice on minimizing exposure, such as using air purifiers, washing bedding frequently, and keeping pets out of bedrooms. 

Allergy test results can also tailor allergy immunotherapy, a treatment designed to desensitize the immune system to specific allergens. This involves administering gradually increasing doses of the identified allergen(s) over time, either through injections or sublingual tablets. A 2023 systematic review found that immunotherapy improves atopic dermatitis severity and patient quality of life.

Patch testing results will help patients avoid jewelry, skincare products, and other household items that can aggravate contact dermatitis. 

When tests show elevated inflammation markers, it indicates a more systemic or severe inflammatory response. This could prompt the healthcare provider to emphasize anti-inflammatory treatments. Prescription medications such as topical corticosteroids or calcineurin inhibitors reduce inflammation in the skin. For severe cases, systemic immunosuppressants or biologic medications may be prescribed to target the immune system more broadly.

Natural anti-inflammatory supplements like omega-3 fatty acids, turmeric (curcumin), and probiotics might also be recommended as complementary therapies to help reduce systemic inflammation and support skin health. 

Preparing for Lab Tests: What You Need to Know

Blood allergy testing involves a routine blood draw from a vein in your arm. This test is straightforward and involves minimal preparation or discomfort. Results typically take a few days to a week. (3) 

Skin prick testing is performed in the office. Tiny amounts of allergens are placed just under the skin's surface with small needles called lancets. About 15 minutes later, the skin is evaluated for allergic reactions. Patients will have their results at the end of their appointment. (4) 

Patch testing involves applying patches with allergens to the skin, which remain in place for 48 hours. After removal, the skin is evaluated for delayed reactions. (4) 

Minor side effects, such as itching, burning, and redness, are common and normal during prick and patch allergy testing. If you experience significant discomfort, contact your doctor.

Before undergoing allergy testing, consult your doctor for advice on avoiding substances that may affect test accuracy. Antihistamines, in particular, should be discontinued for several days before testing, as they can mask allergic reactions. (4) 

Once test results are available, schedule a follow-up appointment with your healthcare provider to discuss the findings and treatment options.

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Key Takeaways

• Lab tests help us better understand and manage eczema by identifying specific triggers and underlying causes that might not be apparent through clinical examination alone. 
• From allergy panels and patch testing to evaluating inflammation markers, these tests provide valuable insights that can guide more personalized and effective treatment strategies. 
• If you suspect that additional testing might be beneficial for managing your eczema, consult an integrative dermatologist. By integrating lab results with expert guidance, you can develop a tailored approach to treatment that addresses your unique needs and propels you towards healthier skin.