Microgram Units Made the Postmortem Assay’s Quantification Limits Higher Than They Might Appear
The method reported its lower quantification limits in micrograms per milliliter. Converting those units correctly is essential before comparing its sensitivity with an assay reported in nanograms per milliliter.
The table provided analyte-specific limits
The reported THC lower quantification limit was 0.05 micrograms per milliliter, equivalent to fifty nanograms per milliliter. For THC-COOH it was 0.08 micrograms per milliliter, equivalent to eighty nanograms per milliliter. The detection limits were lower and were separately defined.
A small decimal is not necessarily a lower concentration
One microgram equals one thousand nanograms. Comparing 0.05 directly with a value such as one nanogram per milliliter without converting units reverses the scale. Detection and quantitative reporting also have different acceptance requirements, so those limits should not be interchanged.
Sensitivity constrains the meaning of a negative result
A method can be useful for its intended postmortem applications without quantifying every low concentration another method can measure. A result below this assay’s quantification limit does not establish zero analyte or absence of prior exposure. Identify the original units, matrix and reporting threshold before comparing case results or laboratory capability. None of the analytical limits constitutes a biological boundary between impairment and unimpaired function.
Related analysis: the study’s broader findings and limitations.
