CLSI EP07-Ed3 (R2022): Interference Testing In Chemistry

Researcher using a test tube to perform interference testing in clinical chemistry lab, adhering to CLSI EP07-Ed3 (R2022).

Interferences with clinical laboratory tests can create discrepancies in test results that may lead to patient harm. Although performance is monitored by internal quality control and external quality assessment procedures, laboratories cannot easily detect error caused by interferents. Therefore, CLSI EP07-Ed3 (R2022): Interference Testing In Clinical Chemistry – 3rd Edition provides guidelines to identify and investigate discrepant clinical chemistry results due to potential interferents.

What Is Intereference?

Any measurement procedure, quantitative or qualitative, may be subject to testing inaccuracies. The three main contributors to testing inaccuracy are imprecision, method-specific difference, and specimen-specific difference (interference). Interferences occur when a substance or process falsely alters an assay result. They are classified as endogenous or exogenous sources.

Endogenous VS Exogenous Interference 

Endogenous interference originates from substances present in the patient’s own specimen, causing infection with one’s own bacteria. Here some examples:

  • Metabolites produced in pathological conditions such as diabetes mellitus, free hemoglobin, bilirubin, and lipidemia
  • A dormant pathogen might become reactivated and infect the host, such as in the case of tuberculosis

Exogenous interferences are substances introduced into the patient’s specimen from their environment. Here some examples:

  • Contaminants inadvertently introduced during specimen handling like hand cream or powder from gloves
  • Substances and/or compounds added during specimen preparation and/or patient treatment, such as anticoagulants, drugs, plasma expanders, preservatives, and stabilizers
  • Substances ingested by the patient like alcohol or nutritional supplements like biotin, a type of vitamin B

To perform interference studies, proper planning is required, such as following the guidelines specified in CLSI EP07-Ed3 (R2022).  

What Is CLSI EP07-Ed3 (R2022)?

CLSI EP07-Ed3 (R2022) provides background information, guidance, and experimental procedures for investigating, identifying, and characterizing the effects of interferents on clinical chemistry test results. In clinical chemistry, interference is defined as “a cause of medically significant difference in the measure and test result due to another component or property of the sample.” This guideline is written for a broad spectrum of measurement procedures and measuring systems. Its primary focus is quantitative and qualitative methods with interpretation based on numeric values. Measurement procedures that use serum, plasma, whole blood, cerebrospinal fluid, urine, and most other body fluids can be evaluated for interferents using CLSI EP07-Ed3 (R2022).

CLSI EP07-Ed3 (R2022) and its supplement document EP37-Ed1: Supplemental Tables For Interference Testing In Clinical Chemistry-1st Edition are intended to provide a solid starting point for assessing interference effects. Both documents are not meant to include a complete list of interferents to be tested and do not stipulate that all potential interferents included in CLSI document EP371 are to be tested.

What Is the Objective of CLSI EP07-Ed3 (R2022)?

This guideline is intended to assist manufacturers and medical laboratories, for two purposes:

  1. Characterizing the effects of potential interferents on measurement procedures results by providing relevant information.
  2. Investigating discrepant results that may be due to interferents.

CLSI EP07-Ed3 (R2022): Interference Testing In Clinical Chemistry – 3rd Edition is available on the ANSI Webstore.

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