Terminology Focus
"Interfering substance/interferent" vs. "Influence quantity"

The CLSI effort to harmonize terms occasionally encounters difficulties. Some traditional terms are deeply rooted in the culture of the healthcare testing community, especially in English-speaking countries. The concepts behind internationally recommended terms and definitions, especially in the International Vocabulary of Basic and General Terms in Metrology (VIM 1993), are often hard to understand. These difficulties are usually discussed in the “Note on Terminology” in the Foreword of most CLSI documents.  As stated in these notes, the transition to harmonized terms is evolutionary, and may take place over a series of revisions, as the preferred terms gradually come into common use.  One such term is discussed below. 

When making measurements on clinical samples, one or more substances can be present that can cause misleading result(s).  In CLSI/NCCLS document EP7, Interference Testing in Clinical Chemistry, this is called an interfering substance or interferent, but VIM calls it an influence quantity. Both terms are defined as follows: “quantity that is not the measurand but that affects the result of the measurement (VIM 1993); EXAMPLES: a) temperature of a micrometer used to measure length; b) bilirubin concentration in the measurement of haemoglobin concentration in a sample of human blood plasma.”

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