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How to Read Mold Air Test Results

Picture of mold test results

Let's face it, seeing your air test results for the first time is scary. Giant scientific words like "Scopulariopsis/Microascus" paired with numbers, percentages and more can cause panic in the best of homeowners. So what does it all mean and how do we read our test results? Read on for the breakdown on how to read your test results using a REAL AIR TEST as shown above!


What is an Air Test?

There are many different types of tests to analyze indoor contamination, but in this article, we are focusing on the Air Test. Air Tests are generally recognized as the legal standard for identifying an indoor fungal ecology issue, or mold problem. The process is simple and includes an Indoor Environmental Professional (IEP) utilizing a calibrated pump to draw a measured amount of air through a slide designed to catch mold spores and other particulate. These samples are pulled from numerous locations throughout a building as well as outside (I'll show why further down) and then sent to a laboratory for analysis. Unfortunately, the reports the lab sends back are often daunting and intimidating to read.

Testing Volume

Picture of Mold Test Results Highlighting Sample Size

The first area of focus on the results is the volume. Most samples, or "cassettes" call for 75 L of air to be passed through and is achieved by pulling 15 L per minute at a 5 minute sample time. This is important to note because if a higher or lower amount of air is pulled (higher amount for trying to find more spores in a cleaner space, lower amount for a wall cavity or extremely contaminated area), you could get different data. This volume is always notated and given to the laboratory via a Chain Of Custody, or COC to be used for their calculations.


Mold (Spore) Types

Picture of Mold Test Results Highlighting Mold Types

This is probably the most intimidating column on any air test report, especially if your IEP doesn't walk you through the findings. "How do you say 'Zygophiala/Schizothyrium' and what molds should be concerning" are some of the very first reactions I hear when helping interpret these results for clients. The good news is that most laboratories include a detailed list of the mold types paired with where the molds are found and what health risks can be associated to exposure. The most important part here is to educate yourself and stay hopeful. These names are no reason to panic!


How Many Spores?

Picture of Mold Test results highlighting raw count, count/m³, and total percent

"John, my test results show that the air is 86.8% Aspergillus"! This is a real quote from a real client, so it's important to know what these numbers REALLY mean. Each sample has 3 columns on this particular test. The first column is "Raw Count". This is the number of spores (per type) that the laboratory technician identified during direct microscopic analysis (sounds like a fun job, I know). This is a very important number because the laboratory will use this to calculate the data used to make decisions in remediation or clearance tests. It is also important to note that not all labs do this the same way. Some labs count 1/4 of the sample and extrapolate the data while others count the entire sample and even have 2 independent counts performed. They then use this number to calculate the next column, Count/m³ and this is the number we pay the closest attention to. The laboratory uses the raw count and the volume of air to calculate how many spores of each type would be found in every cubic meter of air in the sample areas. The final column represents the % of the sample that particular mold represents. This is generally not a number we take into consideration as it is just a representation of mold level ratios in this one sample area.

Picture of mold test results highlighting sample locations

As you can see, This particular report has 3 sample areas; Master Bedroom, Upper Hall and Exterior, but why would an IEP test the outside? The outside sample, acts as a control test. This shows what levels and types of molds would be normal to have in your environment and are collected the same way on the same day as the indoor samples.

Picture of mold test results highlighting the controlled outside test levels

Think about it, since there are spores all around us, when you open a window or you bring the dogs in from outside, that air comes into your home. These levels are our control sample and we want our tests to be at or below the outside numbers with no wet molds like Stachybotrys or Chaetomium. This is considered "Normal Fungal Ecology" and they are the levels we want our homes to test at or below.


Other Variables

Picture of mold test results highlighting background particulate

Sometimes, test results can be affected by other variables. As seen in the slide above, background particulate levels are one example. Not only can high levels of background particulate (things like skin cells, dander, pollen etc.) directly affect the laboratory's ability to analyze the sample, they can also be a huge factor in poor indoor air quality. Other examples affecting the samples can include temperature, indoor conditions (like a property being actively wet) or rainy weather outside. It is important that your IEP notates these factors so that the lab results can be properly interpreted before making final determinations.


Clearly, these samples can give a plethora of useful information. These tests can lead us to determine if and where a fungal issue exists and what to do about the problem. It is important to note that these samples are at one point in time. Without comparison to other samples within the same test areas, they will not show if levels are rising or falling. Similarly, without the outside control test, we cannot properly conclude if there is an indoor issue or if the indoor environment is just a result of elevated outside levels. When paired with detailed observations from a trained professional, these results can be an integral part of determining an optimal solution for a successful remediation.

If you are in need of mold testing, an indoor environmental assessment or interpretation of air test results, reach out to us at


Picture of John Naumann ,Certified Indoor Environmentalist and Owner

John is an ACAC Board Certified Indoor Environmentalist that has helped thousands of people dealing with mold and air quality issues in the Greater Pittsburgh & Tri-State area. At Alpha Air Quality, we ensure that families are receiving accurate information, factual testing & assessments, as well as proper mold removal and remediation. John is a top mold expert in the area and serves the community with excellence and experience!



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