I need to have my house tested for mold.  Many companies and inspection services in my area offer mold testing.  Is all mold testing the same?  How can  I be sure that the mold tests conducted in my house are done right?- Barbara 

            Many companies do in fact provide mold-testing services.  They differ in terms of the kind of testing techniques they use, how they actually do testing, how they interpret test results, and of course cost.

            Mold testing may include collecting airborne samples, collecting samples of infested materials for subsequent analysis or collecting transparent sticky tape samples.  The most common service is the collection of airborne mold spores using either culturable/viable or total mold spore sampling techniques.

            Culturable/viable sampling has been (this has changed notably in the last couple of years) the dominant method used by those who provide mold-testing services.  In this method airborne particles (which include mold) are drawn though a multi-holed (usually 400) plate and impacted on a solid mold selective medium contained in a petri dish.  A variety of media are used including malt extract agar (MEA), dichloran glycerol agar (DG-18), and Sabourauds agar Sabs).

            This technique has its advantages and limitations.  The primary advantage is that it is an easy-to-use off-the-shelf technique.  In theory anyone who reads and follows the directions properly can use it.  Users must have a source of culture media and engage an analytical laboratory to conduct mold counts and mold identifications.

            Another advantage is that one can in many cases identify mold types present down to species.  In most cases laboratories only identify mold colonies to the genus level.

            The method has several major disadvantages.  The primary one is that sampling results only affect the concentration of mold spores/particles that are alive (viable) and can grow (culturable) on the culture medium being used.  As such, culturable/viable airborne mold levels are only a fraction of total airborne mold levels.  Typically 80-95% or so of mold spores of individual species that are airborne are not viable at the time samples are being collected.  Mold spores can cause allergic reactions and asthmatic attacks even if they are no longer alive.

            Another disadvantage of this method is the short sampling duration used - typically 1-5 minutes.  Such a short sampling time is at best only a snapshot of what the culturable/viable mold concentration is in the building being sampled.  It is not uncommon for concentrations of airborne mold to vary by a factor of 2-3 or more over the course of a single day when sampling is conducted in the same location.

            Another problem (as it is also true for other methods) is how to interpret sampling results.  Many investigators use guideline values that reflect experience more than scientifically–based relationships.  Commonly 1000 CFU/m³ is used to distinguish between problem and non-problem environments.  Though high numbers (>1000 CFU/m³) are indicative of a mold exposure/health concern, low numbers (<1000 CFU/m³) cannot and should not be used to conclude that a problem does not exist.

            The culturable/viable sampling method is a useful tool in conducting a mold investigation of a building.  It should not be used alone as it gives a relatively incomplete picture of airborne mold levels and potential exposure health concerns.