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Reagent Lot to Lot Verification

Maintaining consistency of results over time is a challenge in laboratory medicine. Each change in reagent lots can adversely affect the consistency and quality of patient results. Good laboratory practice requires evaluation of each new reagent lot prior to use. Assuring lot-to-lot consistency is particularly important for those analytes that are serially measured over time such as hemoglobin A1c, TSH, INR, tumor markers, and liver enzymes.

Manufacturers try to minimize reagent lot-to-lot variation but multiple factors can affect performance of a new reagent. Examples include minor changes in reagent contents, reagent instability, reagent deterioration during transportation or storage, and inaccurate calibration.

Performance of a new lot of reagents should be compared against the existing lot before it is depleted. Three to five patient samples with low, mid and high analyte concentrations should be run with both the current and new lots of reagents. There are no universally agreed upon criteria to accept or reject new reagent lots. The medical director must determine what is acceptable. Factors to consider include method imprecision and clinically significant difference. For most analytes, a difference between reagent lots of less than 10% is acceptable.

Although patient samples are preferred for checking lot to lot variability, other alternatives are permissible.

  1. Reference materials or QC products provided by the method manufacturer with method-specific and reagent-lot–specific target values.
  2. Proficiency testing materials with peer-group–established means.
  3. QC materials with peer-group established means from at least 10 laboratories.
  4. Third-party general purpose reference materials if the material is documented in the package insert or by the method manufacturer to be commutable with patient specimens for the method.
  5. QC material used to test the current lot is adequate alone to check a new shipment of the same reagent lot, as there should be no change in potential matrix interactions between the QC material and different shipments of the same lot number of reagents.
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