Laboratory Analysis and Interpretation of Results
Laboratory analysis and interpretation of results
This domain tests whether you can read a laboratory report correctly and defend the conclusion in writing.
Analytical methods
- Spore trap (non-viable): direct microscopy reporting spores per cubic meter by genus or group (Penicillium/Aspergillus, Cladosporium, ascospores, basidiospores). Fast, but no viability data and limited by morphology.
- Culture: grows colonies, identifies to species, reports CFU. Slow growers lose to Penicillium and Trichoderma, so results are biased.
- PCR / MSQPCR: DNA-based, species-level, works on dead material; ERMI uses 36 species from a dust sample to produce a weighted index.
- Tape lift: morphology of the growth itself; the best evidence that growth, not just settled spores, is present.
Interpretation principles
Composition matters more than total count. Indoor air should resemble outdoor air in genus mix, usually at lower totals. Suspicious findings include one genus dominant indoors while rare outdoors (Penicillium/Aspergillus at 4,000 versus 200 spores per cubic meter outdoors); any Stachybotrys, Chaetomium or Memnoniella indoors; or elevated counts in a room where no growth is visible while another area is heavily contaminated.
ERMI cautions
ERMI scores are sometimes grouped (below 5 lower, above 20 higher), but the index is a screening tool, not a pass/fail clearance test. It reflects the dust reservoir, not current airborne exposure.
Worked example
Indoor: Penicillium/Aspergillus 4,200 spores per cubic meter, Cladosporium 400. Outdoor: Penicillium/Aspergillus 300, Cladosporium 2,100. The indoor Penicillium/Aspergillus ratio is about 14 times outdoor while Cladosporium is lower indoors, indicating indoor amplification rather than outdoor infiltration. Recommend a source investigation.
Traps
Comparing indoor and outdoor samples collected on different days; treating a low total count as clearance; assuming culture results equal exposure; using ERMI as a clearance criterion.