LOD vs LOQ: Why Detection Doesn’t Always Mean Reliable Quantification

In cannabis testing, detecting a compound and accurately measuring how much of it is present are two different things. A laboratory may be able to detect an analyte at a low concentration without being able to quantify it reliably at that same level. 

Understanding the difference between the limit of detection (LOD) and the limit of quantification (LOQ) helps cannabis producers interpret laboratory results and understand what the numbers on a Certificate of Analysis (COA) actually mean, particularly when a result is reported as below the quantification limit. This distinction helps producers recognize what their results can and cannot tell them.

What Is the Limit of Detection (LOD)?

In analytical testing, the matrix is everything in a sample apart from the substance being measured. For cannabis products, this can The limit of detection is the lowest concentration at which an analytical method can distinguish an analyte as present above background noise.

In simple terms, the laboratory can detect a signal indicating that the compound may be present. However, this does not necessarily mean the method can measure its concentration with acceptable accuracy and precision.

LOD is particularly relevant when testing for trace amounts of compounds, such as potential contaminants, where concentrations may be very low.

What Is the Limit of Quantification (LOQ)?

The limit of quantification is the lowest concentration at which a method can reliably measure an analyte with acceptable accuracy and precision.

The distinction is important. A compound may be detectable below the LOQ, but the method has not demonstrated that it can provide a sufficiently reliable numerical measurement at that concentration.

A result below the LOQ does not automatically mean the compound is absent. It means the concentration is below the level at which the method can reliably quantify it.

In practice, LOD tells us whether a compound can be detected, while LOQ tells us whether its concentration can be measured reliably. Both are important for understanding the capabilities and limitations of an analytical method.

Why the Difference Matters in Cannabis Testing

Cannabis products vary considerably in their composition. Dried flower, oils, extracts, edibles, and topicals can all affect sample preparation and analytical performance.

These differences can influence the effective detection and quantification limits of a method. Dilution during sample preparation, for example, can reduce the concentration reaching the instrument. Other substances in the product may also interfere with the measurement.

These interferences, known as matrix effects, can influence the accuracy and reliability of analytical results. We explore this in more detail in our article, Why Matrix Effects Matter in Cannabis Testing.

Health Canada’s Validating analytical methods in cannabis testing guidance specifically warns that an instrument-based detection limit may make a method appear more sensitive than it actually is if sample preparation and dilution steps are not accounted for.

For this reason, the reported LOD or LOQ should reflect the method’s capabilities in the context of the original sample, including sample weight where applicable and relevant dilution factors.

How Should Results Below the LOQ Be Interpreted?

When a result falls below the method’s LOQ, it should not be treated as a reliably quantified concentration.

Depending on the method and reporting procedure, the result may be reported as below the LOQ or using a less-than value, such as “<0.01 mg/g.” That number is an example of a reporting limit, not a universal threshold for cannabis testing.

The important distinction is that a less-than result does not necessarily mean zero. It indicates that the result is below the stated limit, and the report should be interpreted according to the method and its reporting conventions.

It is also important to consider the method’s full validated range. If a sample contains an analyte at a concentration above the upper limit of quantification, the laboratory may need to adjust sample preparation, such as by diluting the sample, before obtaining a reliable measurement.

What Cannabis Producers Should Discuss with Their Testing Lab

When reviewing testing requirements or a COA, producers can ask a few practical questions:

• Do the limits account for sample preparation? Sample weight, extraction, and dilution factors can affect the effective limits for the original product.
• How are results below the LOQ reported? Confirm how less-than results should be interpreted and whether a numerical concentration can be reliably reported.
• Are the limits appropriate for the product being tested? Different matrices can affect method performance, so the method should be suitable for the intended product and analyte.
• Are the reported units and significant digits appropriate? Results, detection and quantification limits, and measurement uncertainty should be reported consistently. Too many decimal places can suggest a level of precision the method has not demonstrated.

These questions can help producers better understand what their laboratory results establish and where the method’s limitations need to be considered.

Reliable Results Start With Understanding the Method

LOD and LOQ provide different but complementary information about analytical performance. The Limit of Detection (LOD) indicates the lowest concentration at which a compound can be distinguished from background noise, while the Limit of Quantification (LOQ) identifies the lowest concentration that can be reliably quantified. Both are important considerations when evaluating a laboratory’s analytical capabilities, but they are only part of the bigger picture. Producers should also consider method validation, technical competence, licensing, and accreditation when choosing a testing partner. Our guide, How to Choose a Reliable Cannabis Testing Lab, explores what to look for beyond a laboratory’s stated testing capabilities.

Health Canada’s guidance emphasizes that these limits should be evaluated and reported in the context of the full analytical method, including sample preparation, dilution factors, measurement units, and the method’s validated range.

PPB Analytical understands that interpreting analytical results involves more than reading a number on a COA. If you have questions about your cannabis testing requirements or need clarification on analytical results, feel free to contact us!

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