Aspergillus/Penicillium, written Asp/Pen on most lab reports, is a single spore-trap category for two separate genera whose spores are so similar under a microscope that a spore trap analyst cannot reliably tell them apart and reports them together.
What is Aspergillus/Penicillium?
On a non-viable air sample, the lab counts small, round, smooth Aspergillus and Penicillium spores as one combined number because microscopy cannot separate them by shape (ASTM D7391 governs the counting, not a genus split). This grouping is why Asp/Pen is usually the dominant line on an indoor spore-trap result: the two genera are ubiquitous indoors and out, so a high Asp/Pen count is normal background unless it sharply exceeds the outdoor control. Only a culturable sample that grows the spores can resolve the actual genus and, sometimes, species.
Why it matters to a mold inspection
The combined count is easy to over-read. A high Asp/Pen number indoors means something only when it clears the outdoor baseline by a wide margin, which is the whole point of the indoor-outdoor ratio; both genera are present in essentially every air sample, so the raw figure alone is not a finding. If species identity matters, for example to flag a clinically relevant Aspergillus, you need a culture, not a trap. The CDC notes that identifying the specific mold is generally unnecessary for the remediation decision, which is moisture control regardless of genus (CDC, About Mold). See how to read a lab report and normal spore counts.
MoldMind keeps the Asp/Pen count tied to its outdoor control and the sampling method, so a high indoor number is always read against baseline rather than reported as alarming on its own.
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Sources
- ASTM D7391: microscopy counts indistinguishable Aspergillus and Penicillium spores as one category.
- CDC, About Mold: species identification is generally unnecessary; the remediation decision is moisture-driven.