Conflicting cannabis lab results: what should you check?

Two numbers do not establish a valid comparison

A numerical difference alone does not demonstrate that a laboratory made a mistake. First establish whether the documents answer the same question. Testing one flower and testing a sample collected differently do not become directly comparable because the cultivar name matches. An older report and a recent finding also need to be read in their respective contexts.

Write down the decision you are preparing: a purchase, a query about a specification or a further examination. Identify what has not yet been established. Until the comparison is clarified, avoid presenting it as definitive evidence of quality or legal compliance. This recommendation does not replace business responsibilities or the assessment applicable to the product.

Step 1: establish the batch, sample and report identities

Collect the complete reports, including attachments. Check the customer, laboratory, report number and version. Record the batch code separately from the sample identifier. What documented quantity was each sample intended to represent? Who collected material, when and from which locations? A similar product name does not establish a documented connection.

Record sampling, receipt and analysis dates, together with documented packaging, storage or processing steps. The same batch does not automatically mean an identical sample or condition. Ask whether the available records support a meaningful comparison. Mark missing information as missing rather than importing it from the other report. An undocumented match remains an unresolved point in the case.

Step 2: check the measurand and reporting basis

Place the analyte, result, unit and reporting basis side by side. Do not compare an individual compound with a sum, or a measured value with a differently defined calculation. For cannabinoids, establish what each laboratory means by THC or total THC. Our calculation guide explains the terms; it does not decide which report is correct.

Check whether the values are expressed on a dry-mass or an as-received basis, for example. Record the method, reporting limits and stated measurement uncertainty. Do not independently replace a below-limit entry with zero. Ask the laboratory to explain differences in definition or presentation before calculating a discrepancy. An unknown detail should stay on the list of questions rather than becoming an assumed fact.

Step 3: ask both laboratories specific questions

Send the comparison questions with the relevant documents you are authorised to share. Ask each laboratory which matrix and parameter it examined, how the result is expressed and what limitations accompany the report. Request clarification of what the stated uncertainty covers and what information is available about sampling and preparation.

If compliance with a specification is to be assessed, first clarify the assessment basis and the agreed decision rule. Uncertainty is not an allowance you can freely subtract from a measurement. Also ask about corrections and which report version is valid. Record responses with a date and named contact. The editorial team cannot decide which finding should govern a real case merely by looking at two numbers.

Step 4: agree any further examination in advance

Reanalysing existing material and taking a new sample do not necessarily address the same question. With the responsible parties, establish what material remains, its condition and which examination could resolve the outstanding point. The suitability and claimed representativeness of a retained sample need separate consideration.

Agree the question, identification, collection or preparation, method, parameters and report format before proceeding. Clarify lawful acceptance, transport, cost, responsibilities and assessment basis. Another laboratory is not more suitable simply because a different number is hoped for. Its service must fit the matrix and task. This guide sets no universal number of additional tests that would be required or legally permitted.

What different results do not automatically establish

Do not simply choose the lowest, highest or commercially most convenient value as the truth. An unchecked average does not establish a sound decision basis either: comparability and an appropriate way to evaluate the results need to be established first. Repeated testing without a defined question can make the record harder to follow without explaining the original discrepancy.

For businesses in Switzerland, product category remains important. Measuring cannabinoids, examining contaminants and assessing legal status are different tasks. One favourable finding does not replace missing parameters or a decision by the responsible specialists. If significant points remain unresolved, record that explicitly instead of inventing a release decision in the worksheet.

Your discrepancy record: compare, ask and document

Use the table for one specific case and enter the information from each report separately. Write ‘not stated’ wherever information is missing. The third column records the question, the responsible contact and, subsequently, the documented answer. If several parameters are involved, create another record rather than mixing different compounds in the same result row.

At closure, state what was explained, which records support the explanation and what remains unresolved. Replacing an old value with a new one does not itself close an open question. Entries stay locally in your browser; they are not sent to a laboratory or CannabisClub.ch and are not stored permanently. Use the copy function to retain the record in your own documentation.

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