“ND” Is Not Always Zero: LOD, LOQ, and Detection Limits on Hemp COAs

ND usually means the laboratory did not detect the named analyte under the method and reporting rules used for that sample. It does not prove that the analyte is mathematically absent.

Every analytical method has limits. Near those limits, the difference between seeing a signal and assigning a reliable number becomes important. A hemp certificate of analysis may therefore use ND, <LOD, <LOQ, or a numerical result for different situations.

The short version

Report entry	Common reading	What it does not establish by itself
ND	Not detected under the stated method and reporting convention	Absolute zero in the entire batch
<LOD	Below the method’s stated detection limit	That no molecules are present
<LOQ	A signal may be present, but below the stated quantification limit	A reliable exact concentration
Numerical result	The lab reported a quantity	Accuracy outside the method, matrix, sample, and uncertainty
NT	Not tested, in systems that use this abbreviation	A passing or absent result

These are reading conventions, not universal definitions. Check the report’s legend and the rules that govern the laboratory.

What the detection limit describes

NIST describes a limit of detection as an estimate of the lowest concentration of an analyte in a sample that can be reliably differentiated from a blank matrix and identified by the analytical method.

The key words are estimate, sample, matrix, and method.

A detection limit is not a permanent property of CBD, THC, CBG, a pesticide, or a metal. It belongs to a measurement process. It can depend on:

• the instrument and detector;
• sample preparation;
• extraction efficiency;
• calibration;
• background signal;
• the physical matrix;
• dilution;
• the amount of material tested; and
• the laboratory’s validated reporting procedure.

A method that detects an analyte in a clean calibration solution may perform differently in flower, oil, gummy, or isolate. That is why a limit should be connected to both the analyte and the matrix.

Detection and quantification are different questions

Detection asks whether the observed signal can be distinguished from the expected background with the method’s stated reliability.

Quantification asks whether the method can assign a numerical amount with acceptable performance.

The limit of quantification is therefore often higher than the limit of detection. There can be a region where the method indicates that an analyte may be present but does not support a reliable reported concentration.

That region is commonly represented as <LOQ. The symbol does not mean “equal to the LOQ,” and it does not supply an exact value for arithmetic.

If a report lists an LOQ of 0.01% and returns <LOQ, do not enter 0.01% as the measured result. The report is saying the result falls below its quantification threshold under its convention. It may also provide a separate LOD or explanatory note.

Why ND cannot be converted to zero automatically

Suppose a method reports ND for delta-9 THC and shows an LOD of 0.005% by mass. The statement supports “not detected under this method at the stated limit.” It does not support “the sample contains exactly 0.000%.”

There are several reasons:

1. An amount below the detection capability may not produce a reliably distinguishable signal.
2. Only the submitted sample was analyzed—not every unit or every part of the batch.
3. Sampling and preparation can introduce additional variability.
4. The report may round values according to a stated rule.
5. Another validated method may have different sensitivity.

Using zero in a total can therefore understate what the report actually establishes. When a calculation requires treatment of non-detects, use the rule specified by the governing method, regulator, study protocol, or qualified analyst. Do not invent one from the abbreviation.

Blanks, noise, and false decisions

Analysts use blank materials to observe signals that can appear even when the target analyte was not intentionally added. Background can come from the matrix, reagents, equipment, carryover, electronics, or data processing.

Detection-limit procedures are designed around the risk of two mistakes: calling background a detection and failing to detect an analyte that is present near the limit. The exact statistical approach depends on the method and validation framework.

This is why “the instrument showed a tiny peak” is not enough. The peak must meet the method’s identification and reporting criteria. Conversely, the absence of a qualifying peak only supports a non-detect at that method’s capability.

Quality controls, calibration checks, blanks, and reference materials help a laboratory show that the analytical run behaved as expected. They do not make the LOD disappear.

Read the report legend

Before interpreting a non-detect, find:

• the laboratory’s definition of ND;
• the LOD and LOQ for the named analyte;
• the units;
• the method or method identifier;
• the tested matrix;
• any dilution factor;
• result qualifiers or footnotes; and
• whether the panel was performed.

Some laboratories show one reporting limit rather than separate LOD and LOQ fields. Others use a method detection limit, reporting limit, action level, or practical quantitation limit. Similar-sounding terms should not be treated as identical without the report’s definitions.

California’s 2026 regulated cannabis rules offer one concrete reporting system: the COA includes the analytical method, instrument, LOD, and LOQ; results below LOQ are shown as <LOQ under the rule’s conditions; results not detected or below LOD are shown as ND; and tests not performed are shown as NT. Other state or private hemp reports may follow different rules.

Units can change the meaning

An LOD of 0.01 can mean very different things depending on the unit:

• 0.01% by mass;
• 0.01 mg/g;
• 0.01 mg/mL;
• 0.01 micrograms per gram; or
• 0.01 mg per package.

Never compare the bare number. Confirm the analyte, unit, matrix, and amount basis.

Percentage by mass can be converted to milligrams per gram when the basis is the same:

1% by mass = 10 mg/g

Therefore, 0.01% by mass equals 0.1 mg/g. That conversion does not automatically produce milligrams per bottle or per gummy. Container mass, liquid density, unit weight, and sampling basis may be needed.

Potency Units Explained covers those distinctions.

Comparing reports from two laboratories

Do not compare ND across two reports until their capabilities are aligned. One laboratory may report ND below 0.01 mg/g while another has an LOQ of 0.1 mg/g and uses ND for everything below that level. The identical abbreviation can therefore describe different evidence.

Compare:

• analyte identity;
• matrix;
• method;
• LOD, LOQ, or reporting limit;
• unit and dry-weight or as-received basis;
• dilution and preparation notes; and
• result convention.

A lower numerical limit is not proof that the entire method is superior. Accuracy, precision, selectivity, calibration range, matrix validation, and quality controls also matter.

A legal threshold is not a laboratory limit

A statutory or regulatory threshold states a legal criterion. An LOD or LOQ states something about a measurement method’s capability. They answer different questions.

If a legal criterion is lower than the method’s quantification limit, <LOQ may not establish that the sample is below the legal criterion. If a non-detect is used in a compliance decision, the governing law, method, decision rule, and measurement uncertainty all matter.

This distinction is especially important for container-level criteria. A percentage result from a small sample cannot be compared directly with a milligram-per-container threshold without the appropriate mass or volume information and a valid conversion.

No front-label “THC-free” statement should be confirmed from the letters ND alone. The claim’s meaning, relevant analytes, report limits, batch match, product matrix, and governing rules must all be checked.

ND on one panel says nothing about another

A cannabinoid non-detect does not establish anything about:

• pesticides;
• heavy metals;
• residual solvents;
• microbes;
• mycotoxins; or
• unlisted cannabinoids.

Each panel has its own analytes, methods, limits, and result fields. A report that did not order a panel may use NT, leave it absent, or omit the page entirely.

Hemp Lab Panels Explained shows how to separate “not detected,” “not quantified,” and “not tested.”

The batch and sample still come first

Even a perfectly explained LOD cannot connect a report to a product. Confirm:

• product and variant;
• batch or lot;
• laboratory sample ID;
• matrix;
• collection and analysis dates; and
• complete report status.

An ND result from an ingredient lot does not automatically describe the finished oil or gummy. An ND result from one flower sample does not prove uniform absence throughout every package.

Use Batch, Lot, Sample ID, and Test Date before interpreting the result table.

A practical reading statement

When a report shows ND, a careful summary looks like this:

The laboratory reported the analyte as not detected in the identified sample using the stated method. The report lists an LOD of [value and unit]. ND does not establish mathematical zero or describe material outside the matched sample and batch.

If the report does not provide enough information to complete that statement, request the full COA or method legend.

Checklist

• Is the correct batch matched?
• Was the relevant panel performed?
• What does this laboratory mean by ND?
• Are LOD and LOQ both shown?
• Which analyte and matrix do the limits apply to?
• What are the units?
• Is the result numerical, <LOQ, <LOD, ND, or NT?
• Is a legal or label threshold being compared in the same unit and basis?
• Does measurement uncertainty or a decision rule affect the conclusion?

The responsible conclusion is often narrower than “zero.” Narrow is useful when it accurately describes what the measurement can support.

Primary sources

• NIST, Limit of Detection
• NIST, Detection and Quantification Capabilities
• USDA AMS, Hemp Laboratory Testing Guidelines
• California DCC, Medicinal and Adult Use Cannabis Regulations, revised January 1, 2026