What “Not Detected” Means on a Laboratory Report

What the phrase means

Every laboratory method has a floor: a level below which it can’t reliably tell whether something is present. “Not detected”, often written “ND” or “n.d.”, means the result fell below that floor. The substance might be absent, or present at a level too low to measure. Neither possibility can be distinguished by that method.

“Not detected” in different tests

When ND is reassuring

An ND result is meaningful when the detection limit is stated and sits well below the legal or reference limit. For mercury, with a GB supplement limit of 0.1 mg/kg,^[1] an ND with a limit of 0.01 mg/kg tells you the level is at most a tenth of the maximum. An ND with a limit of 0.2 mg/kg tells you almost nothing, because the product could still exceed the legal limit.

When the limit is missing

A report that says “ND” without a detection limit can’t be judged. That isn’t necessarily a sign of a bad product, but it is a gap. Ask the brand or laboratory for the limits; see what detection limits mean.

Pesticide screens and ND

A pesticide screen may test hundreds of substances. “No pesticides detected” means none of the substances on that list was found above its limit. Substances not on the list weren’t tested. A good report includes or links to the list.

Microbiology and ND

For pathogens such as Salmonella, results are usually “not detected in 25 g” or “absent in 10 g”. A larger tested portion gives more confidence. For counts, “< 10 cfu/g” is the method’s lower reporting limit; see microbiological testing.

Why “zero” claims are misleading

Marketing sometimes turns ND results into “zero heavy metals” or “metal-free”. That overstates what a laboratory can show, and shilajit’s rock origin makes trace metals likely; see “pure” and “zero metals” claims.

ND and daily exposure

For long-term exposure estimates, some people treat an ND result as equal to its detection limit, a cautious worst case. Multiply that limit by your daily serving in grams to get a maximum daily intake. This conservative approach is sensible for metals that accumulate; see long-term use.

What to ask

1. What was the detection limit?For each ND result.
2. How does it compare with the legal limit?
3. Which substances were screened?For pesticides and mycotoxins.
4. What portion was tested?For pathogens.

Examples in practice

Putting it into practice

Every time you see ND on a report, look for the detection limit and compare it with the GB limit. For pesticides, check the list of substances; for pathogens, the portion tested. If anything is missing, ask the brand.

Why ND results are common

Modern methods can detect very low levels, but many contaminants are absent or present only in tiny amounts in a well-processed product. ND results are therefore common for pesticides, mycotoxins and pathogens on good reports. For metals in shilajit, numerical results are more common, because trace metals from the source rock are usually present at measurable levels.

In short

ND is only as informative as the limit behind it. A clear limit, well below the legal maximum, turns ND into genuinely reassuring evidence. When the limit is missing or high, ND tells you very little, so ask before you rely on it.

A habit worth forming

Make it a habit to look for the detection limit every time you see ND. Within a few reports, you will spot immediately which ND results are genuinely reassuring and which leave the question open, and you will know exactly what to ask the brand. It quickly becomes second nature.

The bottom line

“Not detected” means below the method’s detection limit, not zero. It is reassuring when the limit is stated and well below the legal maximum, when screens list what they covered, and when microbiology states the portion tested.

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