Q&A Column, 11/13

1. Executive summary of the third report of the National Cholesterol Education Program (NCEP) expert panel on detection, evaluation, and treatment of high blood cholesterol in adults (Adult Treatment Panel III). JAMA. 2001;285:2486 –2497.
2. Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18:499–502.
3. Mora S, Rifai N, Buring JE, Ridker PM. Fasting compared with nonfasting lipids and apolipoproteins for predicting incident cardiovascular events. Circulation. 2008;118:993–1001.
4. van Deventer HE, Miller WG, Myers GL, et al. Non-HDL cholesterol shows improved accuracy for cardiovascular risk score classification compared to direct or calculated LDL cholesterol in a dyslipidemic population. Clin Chem. 2011;57(3):490–501.
5. Expert panel on integrated guidelines for cardiovascular health and risk reduction in children and adolescents: summary report. Pediatrics. 2011;128 (suppl 5):S213–256.
6. Miller WG, Myers GL, Sakurabayashi I, et al. Seven direct methods for measuring HDL and LDL cholesterol compared with ultracentrifugation reference measurement procedures. Clin Chem. 2010;56(6):977–986.
7. Mora S, Rifai N, Buring JE, Ridker PM. Comparison of LDL cholesterol concentrations by Friedewald calculation and direct measurement in relation to cardiovascular events in 27,331 women. Clin Chem. 2009;55(5):888–894.

Alan T. Remaley, MD, PhD
Section Chief, Lipoprotein Metabolism Laboratory Cardiopulmonary Branch
National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Md.
Member, CAP Chemistry Resource Committee

 

[pulledquote]Q. We have traditionally verified new lots of reagents by running our two levels of quality control. If we don’t see any change in the mean values for either level, we put the reagents into use. On some tests (for example, tumor markers like CEA), we also run a small number of patient samples, covering a medically relevant range, in parallel on the new lot and current lot, but we don’t do this for the vast majority of the assays we run. Some of the other CAP-accredited labs in the local area have told us that our practice is not acceptable.[/pulledquote]

A. It is possible that your practice of using QC for lot-to-lot validation is acceptable, but it really depends on the nature of the QC samples you are using. This issue is addressed in two checklists (all common and chemistry and toxicology). They are respectively:
COM.30450 New Reagent Lot Confirmation of Acceptability. “New reagent lots and/or shipments are checked against old reagent lots or with suitable reference material before or concurrently with being placed in service.”

CHM.13400 Calibration/Calibration Verification Criteria. “Criteria are established for frequency of recalibration or calibration verification, and the acceptability of results.”

Both require that new reagent lots and/or shipments be tested against old/current lots prior to being placed into service “…to ensure that calibration with the new lot of reagent maintains consistent results for patient specimens.”

Both emphasize that patient specimens are the best material to use. However, several alternatives are specified in COM.30450:

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 based on interlaboratory comparison that is method specific and includes data 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. Commutability between reference materials and patient samples can be demonstrated using the protocol in CLSI EP14-A2.

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.

If your QC material is provided by the method manufacturer with method- and lot-specific target values, or if it has peer-group–established means based on at least 10 laboratories, then your practice would be acceptable. Otherwise, you cannot use your QC material to verify a new lot of reagent (though it can be used to verify a new shipment of the same lot, as indicated in No. 5 at left).

Gary L. Horowitz, MD
Medical Director, Clinical Chemistry, Beth Israel Deaconess Medical Center
Associate Professor of Pathology, Harvard Medical School, Boston
Chair, CAP Chemistry Resource Committee

David N. Alter, MD
Spectrum Health System, Grand Rapids, Mich.
Vice Chair, CAP Chemistry, Resource Committee

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Dr. Kiechle is medical director of clini­cal pathology, Memorial Healthcare, Hollywood, Fla. Use the reader service card to submit your inquiries, or address them to Sherrie Rice, CAP TODAY, 325 Wau­ke­gan Road, Northfield, IL 60093; srice@cap.org.