In an article in the July issue of Clinical Laboratory News, Alicia Algeciras-Schimnich, PhD, an associate professor of laboratory medicine and pathology at the Mayo Clinic in Rochester, Minnesota, discusses the importance of lot-to-lot reagent consistency, along with strategies labs can employ to ensure that lot variations don’t affect quality control material or patient sample performance. Verifying new reagent lot performance is not only a good laboratory practice, but laboratory regulations and accreditation standards also require the evaluation of each new reagent lot prior to use, according to Algeciras-Schimnich, who also is director of Mayo’s Clinical Immunoassay Laboratory and associate medical director of operations for Mayo Medical Laboratories.

Each new reagent lot can potentially affect quality control material and/or patient sample performance, the author emphasizes. “Multiple factors can affect performance of a new reagent lot, including changes in a critical reagent material or in stability of the reagents, reagent damage during transportation or storage, or incorrect calibration.” Clinical lab practices for lot-to-lot verification can also vary significantly, from testing just a few samples to as many as 20 to 40 samples with each new lot. What’s been lacking is a standardized protocol or guideline to help laboratories with lot-to-lot verification, says Algeciras-Schimnich.

The Clinical and Laboratory Standards Institute (CLSI) responded to this information gap by publishing EP26-A—User Evaluation of Between-Reagent Lot Variation. The new guideline “takes into consideration the resource constraints of the clinical laboratory and uses as few patient samples as possible,” explains Algeciras-Schimnich.

The guideline’s protocol is divided into two parts. The first involves gathering data to provide a number of parameters. These include the “maximum difference between the two reagents lots that would be acceptable without having an adverse clinical impact (critical difference); the laboratory-observed method imprecision,” and the statistical power needed to help detect important lot-to-lot changes, according to the article. Algeciras-Schimnich suggests this information would help determine the number of samples that would need to be tested, in addition to the rejection limit needed “to assure the critical difference is detected.”

The second part verifies the new reagent lot by “testing the determined number of patient samples with both lots of reagents, calculating the average concentration differences between the two lots and analyzing acceptability of the new lot based on the rejection limit established during the first phase,” says Algeciras-Schimnich.

This new protocol should help labs adopt a standardized and practical lot-to-lot verification process within the current healthcare environment’s resource constraints, notes Algeciras-Schimnich.

Read "Tackling Reagent Lot-to-Lot Verification."