How Accurate is Potency Testing?

How accurate is potency testing? California NORML and Project CBD conducted a "Ring Test" in which identical samples were sent to ten lab testing facilities in order to compare results.
By Dale Gieringer and Arno Hazekamp On January 27, 2014
Cannabis Lab Testing

Originally published in O’Shaughnessy’s.

RING TEST: A standard procedure in the analytical testing industry for external quality-control assurance, in which identical samples are sent to a variety of testing facilities in order to compare results.

Want to know the potency of your medicine? How much, if any CBD, does it contain? Has it been sprayed with dangerous pesticides? Is it infested by molds or bacteria? The only way to answer these questions for sure is to have it tested by an analytical lab.

Many labs now offer testing services for the medical cannabis industry. How accurate are the results they provide?

Our investigation was launched in the winter of 2010/11. An identical set of samples was submitted to 10 labs. The labs were asked to measure THC, CBD, and CBN, the three major cannabinoids for which testing is generally available. To encourage participation, the identity of the labs was kept confidential; in this report they are identified by numbers only (Lab 1, 2 etc.).

In most cases, lab results were consistent to within 20% of each other. To some degree, the differences in results might be explained by natural variations in the consistency of the cannabis samples used; to some degree, by differences in lab procedures. In certain cases, there were glaring discrepancies suggesting laboratory error. Three of the 10 labs performed poorly on half the tests. Particularly in the case of liquid alcohol extracts, test results were troublingly inconsistent. Nevertheless, the general results showed good agreement between most lab results involving herbal samples. Lab performance can be expected to improve in the future as the industry responds with improved standards.

This piece was reprinted by Project CBD with permission. It may not be reproduced in any form without approval from the source.

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