How to Read a Mold Lab Report

A mold lab report can be intimidating. Scientific genus names, numbers in per-cubic-meter units, columns you've never seen before. This guide walks through the elements of a typical report and what each actually means.

The Header Information

Every legitimate lab report starts with the basics:

• Lab name and accreditation. Look for AIHA LAP (American Industrial Hygiene Association Laboratory Accreditation Program). This is the gold standard for environmental microbiology labs.
• Chain-of-custody information. The samples you submitted should match exactly.
• Sample IDs, locations, and volumes.
• Date of collection and date of analysis.

If any of these are missing or inconsistent, the report's reliability is suspect. This is why we use established accredited labs, not the lowest bidder.

The Spore Count Table

The core of the report is a table. Columns are your samples (each indoor location plus the outdoor control). Rows are the mold genera identified. Cells contain counts in spores per cubic meter (s/m³).

For each genus, you're looking at:

• Outdoor baseline: what was in the outdoor air at the time.
• Indoor levels: what was in each tested room.
• The ratio. If indoor is significantly higher than outdoor for a specific genus, there's an indoor source of that mold.

There is no single threshold that separates safe from unsafe. Interpretation is about comparison to the outdoor baseline and presence of water-damage indicator species.

Water-Damage Indicator Genera

Certain molds on the report deserve more attention because they indicate chronic indoor moisture:

• Stachybotrys
• Chaetomium
• Aspergillus versicolor
• Certain Penicillium species
• Ulocladium

Any detection of Stachybotrys or Chaetomium indoors at levels above the outdoor baseline is clinically significant. These molds do not grow outdoors in Southern California in any substantial quantity, so their indoor presence almost always indicates a sustained indoor water source.

Typical Outdoor Background in LA

For context, typical outdoor spore counts in the Los Angeles basin:

• Total spores: 500–10,000 s/m³ depending on season and location.
• Cladosporium: often the dominant genus, 100–5,000 s/m³.
• Ascospores and basidiospores: highly variable.
• Aspergillus/Penicillium: 50–500 s/m³ typical.
• Stachybotrys: rarely detected outdoors, often 0 s/m³.

Your report should show outdoor counts in these ranges. If the outdoor count is unusually low or high, it may affect the indoor-to-outdoor comparison.

Common Misreadings

Some patterns that get misinterpreted:

• High total count, but all outdoor-dominant genera (Cladosporium, basidiospores, ascospores): this usually means outdoor air is entering, not that indoor growth is occurring.
• Low total count but water-damage-indicator genera present indoors: this is more concerning than a high total with only outdoor-dominant genera.
• 'Background' detection of Aspergillus/Pen: single-digit or low-double-digit counts are common and often normal.

What We Provide Beyond the Raw Report

Every mold test we perform includes a plain-English interpretation alongside the raw lab report. The raw numbers matter, but what matters more is what they mean in the context of your home, your water history, and your symptoms. That's what our written report covers.

Related Reading

• Air Sampling vs Surface Sampling: Which Do You Need?
• The Key Components of a Mold Test
• Understanding How Mold Testing Works: The Different Techniques Used