ERMI and HERTSMI-2 are the two DNA-based dust tests most commonly requested by clinicians working with environmentally sensitive patients. They're related, HERTSMI-2 is a focused subset of ERMI, but they measure different things and answer different questions.
How they work
Both tests analyze settled dust: not air. A dust sample is collected (typically by Swiffer cloth or vacuum pump cassette) from a representative area of the home. The lab extracts mold DNA from the dust and quantifies specific species using qPCR (quantitative polymerase chain reaction), the same molecular technique used in clinical microbiology.
DNA-based testing identifies presence regardless of whether the spores are alive or dead. That makes it good for cumulative-exposure assessment but bad for "current state" questions, where air sampling is more appropriate.
ERMI, Environmental Relative Moldiness Index
- Measures 36 species: 26 "Group 1" (water-damage indicator) and 10 "Group 2" (common indoor species)
- Outputs a single index value: calculated as the log sum of Group 1 minus the log sum of Group 2
- Quartile ranking: the index is compared to a national reference database; quartile 1 (lowest) through 4 (highest)
- Original use case: EPA-developed research tool for relative comparison across U.S. homes
HERTSMI-2, Health Effects Roster of Type-Specific Mycotoxins, Statistically
- Measures 5 species: Stachybotrys chartarum, Aspergillus penicillioides, Aspergillus versicolor, Chaetomium globosum, Wallemia sebi
- Outputs a numeric score: weighted scoring system, with thresholds typically cited as <10 (likely safe for sensitive individuals), 11-15 (caution), >15 (re-evaluation recommended)
- Designed by Dr. Ritchie Shoemaker as a focused screening tool for CIRS-sensitive patients
When to use each
| Scenario | Likely best test |
|---|---|
| Routine environmental health screen | ERMI |
| Diagnosed CIRS or MCAS, returning home after treatment | HERTSMI-2 |
| Comparing two homes (relocation decision) | ERMI on both |
| Post-remediation verification of indicator species | HERTSMI-2 |
| Acute "is something here right now?" | Air sampling, not ERMI/HERTSMI |
Common misuses
- Using ERMI as a "safe / unsafe" verdict. ERMI is a relative index, not a safety threshold. A high quartile in one neighborhood may be a low quartile in another.
- Trusting a HERTSMI-2 score without context. The score is meaningful only alongside a building inspection. A low score in a visibly water-damaged home means the dust didn't settle in the area you sampled, not that the building is fine.
- DIY sampling. Self-collected dust samples are commonly contaminated by outdoor dust, vacuum cleaner residue, and cross-contamination. Lab-grade results require lab-grade collection.
How PureSpec runs these tests
- Site walkthrough to identify representative sampling locations and rule out collection contamination risks
- Vacuum-pump cassette dust collection in 2-3 rooms
- Chain-of-custody packaging and shipping to an accredited lab (Mycometrics is the most-cited reference lab for ERMI/HERTSMI-2)
- Lab analysis (typically 5-7 business days)
- Written report tying the lab numbers back to building observations and your specific clinical question
Want to talk through which test fits your situation? Book a consultation or call (321) 324-7756.
