How to Read a Mold Lab Report

A new inspector's first spore-trap report looks like a wall of Latin names and numbers, and the temptation is to scan for the biggest figure and call it the answer. The biggest number is rarely the finding.

How do you read a mold lab report?

Read it as four linked pieces, not one number: the method (direct microscopy or culturable), each genus or group, the count per cubic meter, and the same-day outdoor pairing. The result is the relationship between the indoor and outdoor columns and which genera dominate — not the single highest count (AIHA, Green Book).

A lab report quantifies; it does not interpret. It hands you organized data and leaves the judgment to you, which is why two inspectors can read the same report well or badly. The skill is knowing which fields carry the finding.

What is the difference between raw count and count per cubic meter?

The raw count is how many spores the analyst actually counted on the slide; the count per cubic meter is that raw count converted using the air volume you collected. The lab divides the raw count by your sample volume — flow rate times time — to produce the concentration you compare against outdoors (ASTM International, D7391).

This is why the collection parameters matter to the reading. If the indoor and outdoor samples were run at different volumes, their per-cubic-meter numbers are not directly comparable, and a high concentration can be an artifact of a short sample rather than a real signal. Always confirm the indoor and outdoor pair shared flow and duration; the volume math is covered in air pump calibration.

What does "Aspergillus/Penicillium" mean on the report?

It is a combined category, not a single organism. Under direct microscopy, the small round spores of Aspergillus and Penicillium — and several related genera — look alike, so the lab groups them rather than guessing a species (ASTM International, D7391). A high Aspergillus/Penicillium count tells you that group is elevated; it does not name the species.

Treat the group as a flag, not an identification. If species identity changes the answer — a health concern or a specific organism in question — that needs a culturable or molecular method, not a spore trap. Reporting a spore-trap "Aspergillus/Penicillium" result as a named species is a misreading, and a careful reviewer will catch it. The method split is in spore trap vs culturable.

How do you turn the report into a finding?

State the indoor and outdoor totals, name the dominant genera in each, flag any water-damage indicators (Stachybotrys, Chaetomium) elevated indoors against outdoors, and connect that to the building conditions you observed. Stop short of a pass/fail number, because none exists (EPA, Mold Remediation in Schools and Commercial Buildings; CDC, Mold: Basic Facts).

The finding lives in the comparison plus the genera plus the moisture context — the report data is the evidence, your observed conditions are the why. A defensible narrative reads the report as input to judgment, not as a verdict that writes itself.

MoldMind ingests the structured lab fields — method, genus or group, raw count, volume, count per cubic meter, the outdoor pair — validates the volume math, flags indicator species, and drafts the comparative finding for your review. See the sample report for how a raw lab report becomes a written assessment.

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Sources

• ASTM D7391 — raw-count-to-concentration conversion; Aspergillus/Penicillium grouping.
• AIHA, Green Book — comparative reading against the outdoor control.
• EPA, Mold Remediation in Schools and Commercial Buildings — no pass/fail number.
• CDC, Mold: Basic Facts — no acceptable-level standard.