What "Non-Detect" Actually Means on a Lab Report

A laboratory report can contain a long column of “ND” results. It is tempting to read that as a column of zeros. The report is making a more limited statement.

Non-detect describes a result under an analytical method and reporting convention. Understanding that convention is part of reading the result.

Start with the report legend

Laboratories distinguish between limits used for detection, reliable quantitation and reporting. These terms are related, but they are not interchangeable. A report may define ND against its reporting limit rather than the lowest signal an instrument could detect.

EPA’s method-detection-limit explanation also shows why sensitivity belongs to the analytical procedure and laboratory performance, including background contamination. It is not simply an instrument’s ability to “see” a molecule.

Before comparing two reports, find their definitions, units and method names. Identical abbreviations do not guarantee identical reporting rules.

A small example

Suppose a report defines ND against a reporting limit of 2 ng/L. An ND entry would not establish that the concentration is exactly zero. Nor would it assign a particular value to any concentration below that limit.

The limit is not automatically a health standard. A regulatory value answers a separate question and may use a different sampling design or averaging rule. Detection and compliance should not be treated as synonyms.

Check what was included

A panel covers its listed substances. It cannot establish the absence of all compounds in a larger chemical family, and one sample does not describe every future lot.

Look for the sample identifier and dates, individual analytes, units, limits and quality-control notes. Check whether the report is preliminary, final or amended. If accreditation matters to your decision, confirm the relevant method’s scope rather than relying on a laboratory name alone.

An example from our records

The Eurofins summary identifies job 380-188240-1, generated December 29, 2025 and marked preliminary. Its bottled-water sample was collected December 10, 2025.

The EPA 537.1 PFAS panel reports 18 compounds as ND, each with a 2.0 ng/L reporting limit. That is a finding about those compounds in that sample. It is not a statement that every PFAS was tested or that every bottle contains an absolute zero.

The wider report also contains measured results and qualifiers. Calling the whole package “all contaminants non-detect” would erase that information.

When you see ND, read across the row and then check the legend. The result becomes useful when its limits remain attached.