Alternaria Alternata (M6) IgE: What Your Mold Allergy Test Result Means

Sample type: Serum

Other names: Alternaria Alternata (M6) IgE, M006 IgE Alternaria Alternata, M006-IgE Alternaria Alternata, Alternaria Alternata IgE, Alternaria Alternata Mold IgE, Alternaria Alternata M6, Alternaria M6 IgE, A. Alternata IgE, Alternaria Alternata Immunoglobulin E, Alternaria Alternata IgE High, Alternaria Alternata IgE Normal Range, Alternaria Alternata IgE Allergy, Alternaria Alternata (M6) IgE High, IgE M6, M006 IgE, Alternaria Tenuis IgE, A. Tenuis (M6) IgE, Alternaria Tenuis M6, Mold Allergy Test IgE, Allergen Alternaria Alternata IgE, Alternaria Alternata Allergen, Allergy to Alternaria Alternata, Alternaria IgE Antikoru (Turkish), Alergia Alternaria Alternata (Spanish), Alternaria Alternata Allergie (German/French)

Quest Diagnostics

Written June 10, 2026

Updated June 10, 2026

By Healthmatters Editorial Team

Peer-reviewed sources

Class 0 (<0.1 kU/L)

Class 0 — Below 0.10 kU/L — Non-Reactive No Alternaria alternata-specific IgE antibodies were detected at or above the test's reporting threshold. This result indicates no current immunological sensitization to Alternaria mold has been identified. Mold allergy symptoms are less likely to be caused by Alternaria when this test is negative, though other mold species, non-allergic mold irritation, or unrelated environmental triggers may still be contributing to symptoms if present. No further interpretation of this marker is required unless clinical suspicion remains high, in which case a broader allergen panel or skin prick testing with an allergist may be considered.

Class 0/1 (0.10-0.34 kU/L)

Class 0/1 — 0.10–0.34 kU/L — Equivocal A low level of Alternaria alternata-specific IgE was detected, but its clinical significance is uncertain. Quest Diagnostics notes that results in this range are of undefined significance. This may represent very early or low-level sensitization, non-specific binding, or background signal. Symptoms and exposure history are particularly important in interpreting a result at this level — a result in this range does not confirm allergy but does not rule it out either. Repeat testing or additional evaluation with an allergist may be warranted if symptoms are present.

Class 1 (0.35-0.69 kU/L)

Class 1 — 0.35–0.69 kU/L — Low Positive A low level of Alternaria alternata-specific IgE was detected, indicating mild sensitization to this mold. Class 1 results confirm that the immune system has produced IgE antibodies against Alternaria, but the degree of sensitization is relatively low. Clinical symptoms, if present, may be mild or may only occur during periods of high outdoor spore exposure (typically late summer to early autumn in temperate climates). Some sensitized individuals at this level experience no symptoms at all. Results should be interpreted alongside symptom history and exposure patterns.

Class 2 (0.70-3.49 kU/L)

Class 2 — 0.70–3.49 kU/L — Moderate Sensitization A moderate level of Alternaria alternata-specific IgE was detected. Class 2 indicates meaningful immune sensitization to Alternaria mold — the immune system has produced a measurable antibody response that is more likely to be clinically relevant than lower class results. Symptoms such as nasal congestion, sneezing, itchy eyes, and coughing may occur during periods of elevated outdoor spore counts. If asthma is present, Alternaria sensitization at this level warrants discussion with a treating physician, as exposure to Alternaria spores can contribute to respiratory symptoms and airway inflammation.

Class 3 (3.50-17.4 kU/L)

Class 3 — 3.50–17.49 kU/L — High Sensitization A high level of Alternaria alternata-specific IgE was detected. Class 3 indicates significant immune sensitization to this mold allergen. At this level, exposure to Alternaria spores is likely to trigger allergic symptoms in susceptible individuals, particularly during peak outdoor spore season (late summer to early autumn). The association between Alternaria sensitization and asthma severity is strongest at higher IgE class levels — individuals with asthma and a Class 3 result should discuss allergen management and exposure reduction strategies with their treating physician or allergist. Allergen immunotherapy may be considered as an option to reduce immune reactivity over time.

Class 4 (17.5-49.9 kU/L)

Class 4 — 17.5–49.99 kU/L — Very High Sensitization A very high level of Alternaria alternata-specific IgE was detected. Class 4 indicates strong immune sensitization to Alternaria mold. This level of sensitization is associated with a high likelihood of allergic symptoms on exposure to Alternaria spores. In individuals with asthma, very high Alternaria IgE is associated with increased risk of severe asthma exacerbations during high-spore-count periods. Evaluation by an allergist is recommended to assess the full clinical picture, develop an allergen avoidance plan, and discuss treatment options including allergen immunotherapy. IgE levels alone do not determine treatment decisions — symptom severity, exposure history, and overall health status are all considered.

Class 5 (50-100 kU/L)

Class 5 — 50–99.99 kU/L — Very High Sensitization A very high level of Alternaria alternata-specific IgE was detected. Class 5 represents strong and well-established immune sensitization to Alternaria mold. At this level, even moderate Alternaria spore exposure is likely to trigger significant allergic symptoms in sensitized individuals. In patients with allergic asthma, Class 5 Alternaria IgE is associated with heightened risk of severe and potentially life-threatening asthma exacerbations, particularly during late summer and early autumn when outdoor spore counts peak. Clinical evaluation with an allergist is strongly recommended. Management may include aggressive allergen avoidance, optimized asthma controller therapy, and consideration of allergen immunotherapy.

Class 6 (>100 kU/L)

Class 6 — Above 100 kU/L — Extremely High Sensitization An extremely high level of Alternaria alternata-specific IgE was detected. Class 6 represents the highest category of measured immune sensitization to this allergen. This level of IgE indicates that the immune system has mounted a very strong antibody response to Alternaria mold proteins. In the context of asthma, extremely high Alternaria IgE has been associated with the most severe asthma outcomes linked to mold exposure, including emergency presentations during high outdoor spore count events. Clinical evaluation by an allergist is recommended. Note that very high absolute IgE values do not always directly correlate with symptom severity on an individual level — some patients with Class 6 results have well-controlled symptoms with appropriate management, while others may experience significant reactions at much lower levels. Treatment decisions are made in the context of the full clinical picture.

QUICK ANSWER

Alternaria alternata (M6) IgE measures your immune system's IgE antibody response to Alternaria alternata — a common outdoor mold and one of the most clinically significant mold allergens associated with asthma.

A positive result means your immune system has produced IgE antibodies against Alternaria mold. The higher the level, the greater the degree of immune sensitization — though sensitization does not always cause symptoms.

Quick result lookup (patient-facing):

Your result (kU/L)	What it usually means
Below 0.10	Negative — no detectable sensitization
0.10–0.34	Borderline / equivocal — significance uncertain
0.35–3.49	Positive sensitization — mild to moderate
3.50–17.49	High sensitization
Above 17.5	Very high sensitization

Clinical interpretation at a glance:

Level	Typical clinical meaning
Negative	Alternaria sensitization not detected — symptoms are less likely to be caused by Alternaria allergy
Low positive (0.35–0.69)	Mild sensitization — symptoms possible, especially during high-exposure periods
Moderate–high (0.70–17.49)	Sensitization more likely clinically relevant — discuss with clinician if symptoms are present
Very high (above 17.5)	Strong sensitization — interpret alongside symptoms and exposure history; discuss with allergist if asthma is present

IgE allergy class interpretation (Quest Diagnostics / standard scale):

Result (kU/L)	Class	Interpretation
Below 0.10	0	No detectable IgE — no sensitization identified
0.10–0.34	0/1	Equivocal — clinical significance uncertain; may warrant repeat testing
0.35–0.69	1	Low positive — mild sensitization
0.70–3.49	2	Moderate sensitization
3.50–17.49	3	High sensitization
17.50–49.99	4	Very high sensitization
50.00–99.99	5	Very high sensitization
Above 100	6	Extremely high sensitization

Important: IgE levels do not directly predict symptom severity. A low positive result can cause significant symptoms in a sensitized patient during high-exposure periods; a high result may cause minimal symptoms in someone with low Alternaria exposure. Always interpret alongside symptoms and exposure history.

WHAT IS ALTERNARIA ALTERNATA (M6) IGE?

Alternaria alternata is one of the most clinically significant outdoor mold allergens studied in allergy medicine, and one of the mold allergens most strongly associated with asthma severity and asthma-related hospitalization. On the Quest Diagnostics allergy panel, it is identified by the code M006 (sometimes written M6 or M-6).

The M6 IgE test measures the level of immunoglobulin E (IgE) antibodies specific to Alternaria alternata proteins in your blood. IgE is the antibody class involved in Type I (immediate) allergic reactions — the mechanism behind hay fever, allergic asthma, hives, and anaphylaxis. When a sensitized person inhales Alternaria spores, IgE antibodies on mast cells in the airways trigger the release of histamine and other inflammatory mediators, causing allergy symptoms.

Alternaria alternata vs Alternaria tenuis: These names are sometimes used interchangeably — Alternaria tenuis is an older name for Alternaria alternata, and some lab reports and older literature use "tenuis." They refer to the same organism and the same allergen.

WHAT DOES A HIGH ALTERNARIA ALTERNATA IGE RESULT MEAN?

A high Alternaria alternata IgE result means the immune system has produced significant IgE antibodies against Alternaria mold proteins — indicating sensitization. The higher the class, the stronger the sensitization, and the more likely exposure to Alternaria spores is to trigger allergic symptoms.

Clinical significance of high Alternaria IgE:

Alternaria sensitization is particularly clinically significant compared to many other mold allergens because:

It is strongly associated with asthma severity — Alternaria sensitization is one of the few mold allergies associated with life-threatening asthma exacerbations
It is linked to severe asthma attacks triggered by high outdoor spore counts (particularly late summer and early autumn)
Children with Alternaria sensitization have a significantly higher risk of developing persistent asthma
A positive result in someone with asthma should be discussed with the treating physician

Common symptoms associated with Alternaria sensitization:

Nasal congestion, runny nose, sneezing
Itchy, watery eyes
Coughing and wheezing
Allergic rhinitis (hay fever)
Asthma exacerbations — especially during peak spore season (late summer to early autumn)
Allergic sinusitis
In some patients: hives (urticaria) when consuming yeast- or mold-containing foods

When are symptoms typically worst?

Alternaria spore counts peak in late summer and early autumn in temperate climates (typically July–October in the Northern Hemisphere). Spores are highest in warm, dry, windy conditions — especially in the afternoon. In hot, dry climates (US Southwest, Mediterranean), spore season may extend longer.

WHAT DOES A LOW OR NEGATIVE ALTERNARIA IGE RESULT MEAN?

A result below 0.10 kU/L means no detectable Alternaria-specific IgE was found — indicating no current sensitization to this mold.

A result between 0.10 and 0.35 kU/L is considered equivocal by Quest Diagnostics — the significance of these low-level IgE values is uncertain. They may represent very early sensitization, non-specific binding, or background noise. Clinical context determines whether further evaluation is warranted.

A negative result does not rule out mold sensitivity entirely — other mold species (Cladosporium, Aspergillus, Penicillium, Helminthosporium) have separate IgE tests and may be relevant if Alternaria is negative but symptoms persist.

HOW COMMON IS ALTERNARIA ALLERGY?

Alternaria alternata is one of the most widespread mold allergens globally, but sensitization rates vary significantly by geography and population:

Approximately 5% of the general population is estimated to be sensitized to Alternaria
Among people with allergic asthma, sensitization rates are substantially higher — studies report 15–30% in temperate climates and up to 38% among inner-city children with asthma in the United States
Sensitization is more common in warm, dry climates where outdoor Alternaria spore counts are highest — including the US Southwest, Mediterranean, and parts of Australia
In children, reported sensitization rates vary dramatically by region — from less than 1% in Austria to 50% in Arizona
Alternaria is the most common mold allergy among children with asthma in US inner-city populations

This geographic and population variability means a positive result is clinically more meaningful in high-exposure regions and in patients with asthma or known atopic conditions.

WHERE IS ALTERNARIA MOLD FOUND?

Alternaria alternata is primarily an outdoor mold found in soil and on decaying plant material. It is the most prevalent mold in dry, warm climates and a significant agricultural pathogen affecting grains, fruits, and vegetables.

Outdoor sources: Soil, dead vegetation, compost, leaf piles, crop residue, hay, straw, and decaying wood. Spore counts are highest in warm, dry, windy weather — particularly in the afternoon.

Indoor sources: Alternaria can enter indoors through windows, doors, and HVAC systems. Indoor growth occurs primarily in areas with moisture: bathrooms, basements, window frames, carpet, drywall, and HVAC components. Indoor concentrations correlate with outdoor levels.

Peak season: Late summer to early autumn in temperate climates. In dry, warm regions, elevated counts may persist longer.

MANAGING ALTERNARIA MOLD ALLERGY

Exposure reduction:

Monitor outdoor mold counts (similar to pollen forecasts) and limit outdoor time when counts are high
Wear a mask when gardening, raking leaves, or working with plant material
Keep indoor humidity below 45% — use dehumidifiers in basements and bathrooms
Use HEPA-rated air filters and change HVAC filters regularly
Fix plumbing leaks and water intrusion promptly — moisture control is the most effective indoor mold prevention
Use exhaust fans in bathrooms and kitchens
Remove carpet from bathrooms and basements

Medical management:

Options typically discussed with an allergist or treating physician include antihistamines, nasal corticosteroids, decongestants, anti-inflammatory medications (such as montelukast), and allergen immunotherapy (allergy shots or sublingual immunotherapy), which may help build tolerance to Alternaria exposure over time.

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ALTERNARIA ALTERNATA (M6) IGE

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Frequently Asked Questions

Can Alternaria IgE levels go down over time?

Yes. IgE levels may decrease if exposure falls, if the immune response changes over time, or following allergen immunotherapy. However, a lower result does not necessarily mean symptoms will disappear, and a higher result does not always mean symptoms will worsen. Clinical symptoms remain more important than the number alone. If you are retesting after immunotherapy or a change in living environment, discuss the trend in your results with your allergist rather than interpreting any single value in isolation.

Can I have mold allergy symptoms if my Alternaria IgE is negative?

Yes. A negative Alternaria IgE does not rule out all mold-related symptoms. Symptoms may be caused by sensitization to other molds (Cladosporium, Aspergillus, Penicillium, Helminthosporium all have separate IgE tests), non-allergic irritant responses to mold exposure, local allergic responses in the nasal mucosa not always reflected in blood IgE levels, or entirely unrelated environmental triggers. If symptoms persist despite a negative Alternaria IgE, a broader allergy panel or skin prick testing with an allergist may help identify other triggers.

What does Alternaria alternata (M6) IgE mean on my lab report?

Alternaria alternata (M6) IgE measures the level of IgE antibodies your immune system has produced against Alternaria alternata mold. M006 (or M6) is the Quest Diagnostics allergen code for this mold. A result above 0.35 kU/L is considered a positive finding indicating sensitization. The higher the result, the greater the degree of sensitization — though symptom severity also depends on exposure level and individual immune response.

What is a normal range for Alternaria alternata IgE?

A result below 0.10 kU/L is considered non-reactive — no detectable IgE sensitization. Results between 0.10 and 0.35 kU/L are equivocal (uncertain significance). Results of 0.35 kU/L and above indicate positive sensitization, classified in increasing severity from Class 1 (mild, 0.35–0.69 kU/L) through Class 6 (extremely high, above 100 kU/L).

What does high Alternaria alternata IgE mean?

A high result means your immune system has produced significant IgE antibodies against Alternaria mold proteins. This indicates sensitization — your immune system recognizes Alternaria as a threat and is primed to react when you inhale its spores. Higher classes (3–6) are associated with more reactive immune responses and a greater risk of symptoms during high-spore-count periods. Alternaria sensitization is particularly important to discuss with a physician if you have asthma, as it is one of the mold allergens most strongly linked to severe asthma exacerbations.

Is Alternaria alternata the same as Alternaria tenuis?

Yes — Alternaria tenuis is an older taxonomic name for Alternaria alternata. They refer to the same organism. Some lab reports, especially older ones, use "Alternaria tenuis" or "A. tenuis" while others use "Alternaria alternata" or "A. alternata." The allergen (M006) is the same in both cases.

What is M006 IgE on a Quest Diagnostics report?

M006 is the Quest Diagnostics allergen code for Alternaria alternata (also called Alternaria tenuis). "M" indicates a mold allergen, and "006" is the specific allergen number. The full test name is Alternaria alternata (M6) IgE — measuring IgE antibodies specific to this mold species.

Can a positive Alternaria IgE result cause asthma?

Alternaria sensitization does not cause asthma directly, but it is one of the strongest risk factors for asthma development and severity in both children and adults. Exposure to Alternaria spores in a sensitized individual can trigger acute asthma attacks — and high outdoor spore counts have been associated with emergency room visits for severe asthma exacerbations. If you have a positive Alternaria IgE and active asthma, this should be discussed with your treating physician or allergist.

What foods should I avoid with an Alternaria mold allergy?

Some patients with Alternaria sensitization also react to mold-containing foods — particularly fermented foods (wine, beer, vinegar, soy sauce), aged cheeses, mushrooms, and certain fruits and vegetables with mold contamination. However, food triggers vary significantly between individuals and are not universal. This is worth discussing with an allergist if you notice symptoms after eating these foods.

What is the difference between Alternaria IgE and Alternaria IgG?

IgE antibodies drive immediate allergic reactions (the mechanism behind hay fever, asthma, and anaphylaxis). IgG antibodies reflect exposure or immune tolerance and are not typically used to diagnose allergy. A positive Alternaria IgE indicates sensitization and potential for allergic symptoms. A positive Alternaria IgG (tested separately, M006-IgG) indicates exposure without necessarily indicating clinical allergy.

Clinical Sources & References

All our content is backed by peer-reviewed studies, academic research, and trusted medical sources. We’re committed to accuracy and transparency — see our editorial policy for details.

Exposure to Alternaria alternata in US homes is associated with asthma symptoms

J Allergy Clin Immunol. · 2006 View source ↗
Molds and respiratory allergy- part 1

MOJ Immunol. · 2015 View source ↗
Is sensitization to Alternaria alternata a risk factor for severe asthma? A population-based study

J Allergy Clin Immunol. · 1999 View source ↗
Alternaria Sensitization and Allergy in Children and Adolescents: A Retrospective Diagnostic Study

J Asthma Allergy. · 2025 View source ↗

Article Review Log

Last reviewed June 10, 2026

Originally published June 10, 2026

Reviewed by HealthMatters Editorial Team

Written by Healthmatters Editorial Team

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Alternaria Alternata (M6) IgE: What Your Mold Allergy Test Result Means

QUICK ANSWER

WHAT IS ALTERNARIA ALTERNATA (M6) IGE?

WHAT DOES A HIGH ALTERNARIA ALTERNATA IGE RESULT MEAN?

WHAT DOES A LOW OR NEGATIVE ALTERNARIA IGE RESULT MEAN?

HOW COMMON IS ALTERNARIA ALLERGY?

WHERE IS ALTERNARIA MOLD FOUND?

MANAGING ALTERNARIA MOLD ALLERGY

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