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Reporting Non-Detects
How do I correctly report non-detected analytes? Incorrectly reported non-detects cause many preventable not acceptable evaluations. This article will focus on less than reporting which is the most common method of reporting non-detects.
Reporting non-detects as less than values implies reporting a range of values. For example, a reported
value of "< 4" implies a range of values from 0 to 4. There are two possible options for your
evaluation when you report a less than. The first option is when the analyte was not added to the
sample (also know as a "not spiked" analyte).
The second option is when the sample was spiked.
Spiked Sample
When the analyte is spiked in a sample, less than reporting is acceptable if the given range is within the acceptance limits and zero is the lower acceptance limit. This initial case can be viewed in the table below.
If the reported value contains a less than "<" symbol, then it is acceptable
only if the lower acceptance limit is zero and the reported range is also
within the upper acceptance limit.
| 4 |
2 |
0 - 5 |
Acceptable |
| < 4 |
2 |
0 - 5 |
Acceptable |
| < 4 |
2 |
1 - 5 |
Not Acceptable |
| < 4 |
2 |
0 - 3.5 |
Not Acceptable |
| 0 |
2 |
0 - 3.5 |
Acceptable |
Important Note A non-numeric reported value such as "BDL" or "ND" will not be evaluated.
Non-Spiked Sample
If the reported value is zero or contains a less than "<" symbol, the reported
value is acceptable when the analyte is not spiked. If the reported value is a number other than zero or
contains a greater than ">" symbol, then the reported value is not acceptable.
| 0 |
0 |
Acceptable |
| < 1 |
0 |
Acceptable |
| 1 |
0 |
Not Acceptable |
Important Note A blank reported value is not evaluated.
* For example purposes, the assigned value is assumed to be equal to the mean.
Michael Haller may be reached by email at m.haller@apgqa.com or by phone at 800.272.4442.
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