Your lab sent back a page of species names and numbers. This tool turns them into a plain reading of which moulds are elevated, where the water probably is, and what it is feeding on.
What this tool does. MSQPCR is a DNA test. A dust sample from your home is analysed for a fixed list of mould species, and the lab reports how much of each one it found. Those raw numbers are hard to read on their own, because “a lot” of one species is normal and “a little” of another is not. This tool compares every result against what is normal for that species, then tells you what the pattern suggests about the building.
You will work with three numbers. They are worth two minutes before you start.
SE/mgspore equivalents per milligram
The number your lab reports for each species — how much mould DNA was found in the dust, expressed as the number of spores it would take to produce that much DNA, per milligram of dust. This is the only number you type in. Everything else is calculated from it.
× GMtimes the geometric mean
The geometric mean (GM) is the typical level of that species in an ordinary home — a reference point, one per species, set from thousands of houses. × GM is your result divided by that reference. ×2 is unremarkable. ×200 means two hundred times more than a normal house, which is not something dust tracked in on shoes can do. It is the single most useful column on the page, because it puts every species on the same footing. Which set of reference levels is used is your choice — see Step two.
H2HERTSMI-2 points
HERTSMI-2 is a five-species scoring method developed by Dr Ritchie Shoemaker to answer one narrow question: is it safe for a person with mould illness to live in this building? Five indicator species each earn 0, 4, 6 or 10 points depending on how high they are. The points add up to a score out of 50.
Step one
Choose your test panel
Labs sell several different panels, and each one covers a different number of species. Pick the one you ordered and the table below will show only those species — so you are not hunting for rows your report doesn’t have.
Step two
Choose your reference set
The × GM column compares your result to the level of that species in an ordinary home, and that reference comes from a survey of real houses. Three such surveys have been published, and they are the three options below. If your home is in North America, use the default — United States, 2006. It is the set your lab used, so the figures here will match your report. If you are in Finland, Scandinavia or a comparable northern climate, the Finnish set is closer to the housing around you. The 2019 American set is worth a second look if your home is pre-1978.
Step three
Name your samples
One sample is one dust collection — usually one room or one floor. Add a column for each one so you can read them side by side.
1
Name each sample after the place it came from, not after the lab’s sample number. Primary Bedroom, Basement, Main Floor — you want to be able to read the results without a key. Click a name to edit it.
2
Two or three samples tell you far more than one. A single result tells you the house has mould in it, which every house does. Two results — one from a room you suspect and one from a room you don’t — tell you whether the problem is localised, and roughly where it sits.
3
Keep the comparison honest. Samples are only worth comparing if they were collected the same way, over a similar area, and at roughly the same time. Dust that has been accumulating for two years will read higher than dust from a room cleaned last week — that difference is about the cleaning, not the mould.
4
Add the outdoor or control sample if you have one. Some labs supply one. It sets the baseline for what is simply blowing in from outside, and it is the fastest way to see whether an elevated species has an indoor source.
Step four
Enter your lab results
Type the SE/mg figure from your report into the first column for each species. The × GM and H2 columns fill in and colour themselves as you go. Leave a species blank, or enter 0, for “not detected.” Tap any species name to read what it is, what it grows on, and what it produces.
What your results mean
Written out in plain language, sample by sample — what is elevated, what kind of moisture that pattern needs, and where in a building it usually turns out to be.
Reading the colours
Species shading — × GM
0–10×Normal — within the range of an ordinary house
10–50×Moderately elevated — a minor or emerging problem
50–100×Significantly elevated — almost certainly an indoor source
>100×Extremely elevated — active growth on wet material
A species can be present in large absolute numbers and still be perfectly normal. It is the multiple of the reference — not the raw SE/mg — that tells you something has changed in the building.
HERTSMI-2 — re-entry guidance
Under 11Statistically safe to occupy, even for someone with CIRS.
11 – 15Borderline. Clean or remediate, then re-test before moving back in.
Over 15Unsafe for someone with mould illness. Do not occupy until remediated.
CIRS — Chronic Inflammatory Response Syndrome — is a persistent inflammatory illness triggered in genetically susceptible people by biotoxin exposure, including water-damaged buildings. The HERTSMI-2 thresholds were set for that population, so they are deliberately more cautious than a general-purpose standard.
MSQPCR · DNA-based dust analysisHERTSMI-2 · Shoemaker method× GM · per-species reference levelsReference sets · US EPA AHHS I & II · Finland LUKAS2
Why this tool doesn’t show your ERMI score
1
ERMI was never built to assess one house. The Environmental Relative Moldiness Index was developed by the U.S. EPA as a research index — a way to rank large populations of homes against each other in epidemiological studies. The EPA has said plainly that it is not validated for use on an individual building, and it has never been adopted as a diagnostic standard. It got picked up by the consumer testing market anyway, because a single number is easy to sell.
If your lab printed an ERMI figure on your report, that figure is real and correctly calculated. It just doesn’t answer the question you are actually asking, which is what is wrong with my house and where is it.
2
The arithmetic actively hides problems. ERMI takes the log of every water-damage species, adds them together, then subtracts the log-sum of the common outdoor species. Ordinary spores tracked in on shoes, pets, and open windows therefore pull the score down. A house with real water damage and a lot of outdoor traffic can score lower than a sealed, clean house with no problem at all.
Because it is a log-sum, a trace of many species reads much like a bloom of a few. And a single number cannot say which mould is elevated — which is the only part that tells you where the moisture is.
3
It is very sensitive to how the dust was collected. Where you sampled, how much area you covered, how long the dust had been sitting, and whether the room had recently been cleaned all move the score substantially. Two samples taken in the same house on the same day can differ by several points. A number that unstable is a poor basis for a decision about where to live.
4
So we read the sample species by species instead. Which moulds are elevated, and by how much against their own reference — that is the × GM column, and it is the heart of this tool. From there the pattern tells you something useful: Stachybotrys and Chaetomium need sustained liquid water on cellulose, so they point at a leak. Wallemia and Aspergillus penicillioides live on humidity alone, so they point at a house that runs damp. That is a finding you can act on.
Alongside it we use the HERTSMI-2 score, which is narrower and better-aimed: five species, chosen for their link to health effects in sensitive people, scored against thresholds set for occupancy decisions rather than for research ranking.
How the HERTSMI-2 score is calculated
Each of the five indicator species is scored on its own SE/mg banding, then the five point values are added together for a score out of 50.
Aspergillus penicillioides and A. versicolor score 4 points from 10–99 SE/mg, 6 from 100–500, and 10 above 500. Chaetomium globosum and Stachybotrys chartarum score 4 from 5–24, 6 from 25–125, and 10 above 125 — a much tighter scale, because both need real standing water to grow at all, so any meaningful presence matters. Wallemia sebi scores 4 from 100–499, 6 from 500–2,500, and 10 above 2,500. Anything below the lowest band scores 0.
Only those five species affect the score. Every other species on your panel is read through the × GM column and the interpretation above — they tell you about the building even when they don’t move the HERTSMI-2 number.
Trying to make sense of a mould test result?
If the numbers are elevated — or you’re just not sure what they mean for your home — answer a few quick questions and we’ll point you to the next step that fits where your building actually is.
No sign-up — your next step appears the moment you finish.
Disclaimer. This calculator is an educational tool for interpreting MSQPCR dust-test results and is not medical advice, a diagnosis, or a substitute for a professional assessment. HERTSMI-2 scoring follows the Shoemaker method. Dust sampling reflects one point in time and can be affected by how and where the sample was taken; a clean result does not prove a building is free of mould, and an elevated result does not by itself locate the source. Decisions about occupancy, remediation, or health should be made with a qualified indoor-environmental professional and, where relevant, a physician. Calculated values may differ slightly from a lab’s report where rounding or lab-specific reference means differ.
Reference sets. × GM reference levels are taken from: United States 2006 — U.S. HUD American Healthy Homes Survey I (n = 1,096), U.S. EPA; United States 2019 — American Healthy Homes Survey II (n = 694), Vesper et al., J Occup Environ Hyg 2021;18(1):35–41, values as published in the EPA’s open dataset; Finland 2016 — Täubel et al., “Application of the Environmental Relative Moldiness Index in Finland,” Appl Environ Microbiol 2016;82(2):578–584 (n = 144, LUKAS2 cohort, eastern Finland). These are the only published per-species reference tables at the time of writing; laboratories report against the American set by default. The three ERMI+3 species have never been included in a national survey and carry a nominal reference of 2 SE/mg in every set.
