Q&A column, 4/15

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1. Chang YJ, Chang YJ, Chen LJ, Chung KP, Lai MS. Evaluation of lymph nodes in patients with colon cancer undergoing colon resection: a population-based study. World J Surg. 2012;36(8):1906–1914.
2. Sjo OH, Merok MA, Svindland A, Nesbakken A. Prognostic impact of lymph node harvest and lymph node ratio in patients with colon cancer. Dis Colon Rectum. 2012;55(3):307–315.
3. Iachetta F, Reggiani Bonetti L, Marcheselli L, et al. Lymph node evaluation in stage IIA colorectal cancer and its impact on patient prognosis: a population-based study. Acta Oncol. 2013;52(8):1682–1690.
4. Baxter NN, Virnig DJ, Rothenberger DA, Morris AM, Jessurun J, Virnig BA. Lymph node evaluation in colorectal cancer patients: a population-based study. J Natl Cancer Inst. 2005;97(3):219­–225.
5. Horne J, Bateman AC, Carr NJ, Ryder I. Lymph node revealing solutions in colorectal cancer: should they be used routinely? J Clin Pathol. 2014;67(5):383–388.
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Sanjay Kakar, MD,
Professor, University of California, San Francisco
Benedict Yen Endowed Chair for Chief of Pathology
Veterans Affairs Medical Center, San Francisco
Member, CAP Cancer Committee

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Q. We are establishing a list of maximum allowable dilutions for our clinical chemistry analytes. Are you aware of any reference that would list absurd or invalid values for such analytes, i.e. the endpoint that would determine the most dilutions we would have to do for the highest possible value for that analyte?

A. Response to this question requires a brief review of the definition of analytical measurement range, its verification, and how it affects laboratory operations. All are regularly discussed and debated in laboratories during inspections.

• The analytical measurement range, as defined in the CAP’s chemistry and toxicology checklist, is the range of results that the assay can report without any dilution or concentration. Verification of a manufacturer’s stated AMR is detailed in checklist requirement CHM.13600. Essentially, the lower, middle, and upper ranges of the AMR must be validated. If material is not available to verify the AMR’s exact upper limit, a statement from the medical director citing the highest range verified in the procedure is sufficient. If patient results are higher than the material used to verify the AMR but less than the AMR, they can be reported as they are. For example: AMR = 0–1,000 ng/dL but material available only up to 700 ng/dL; results between 700 and 1,000 ng/dL can be reported.
• In many cases, the manufacturer will have verified extended ranges beyond the AMR using recommended manual or autodilution/concentration protocols. In this situation, reporting of results up to those limits is also acceptable after the AMR has been verified (CHM.13710). This range reflects the reportable range verified by the manufacturer.
• Results greater than the AMR or range verified by the manufacturer should be reported using the “greater than” symbol.
• In situations where the desired results are greater than the AMR or range verified by the manufacturer (dilution to endpoint), CHM.13720 in the CAP checklist requires the laboratory director to specify and document what the maximum dilutions are on an analyte-by-analyte basis. This will require dilution studies to confirm result linearity in this range.

There is no such thing as an “absurd” or “invalid” endpoint/maximum allowable dilution value. There is only validated and nonvalidated dilution. It is up to the laboratory director in conjunction with the clinical staff and vendor to determine what the maximum dilutions will be. For example, it is not unreasonable for creatine kinase to be “diluted to endpoint” because in extreme rhabdomyolysis CK values greater than the AMR should be reported to monitor response to treatment. This can also be applied to many tumor markers for the same reason.

1. College of American Pathologists. CHM.13600 AMR verification. In: Chemistry and toxicology checklist. April 2014:15.
2. College of American Pathologists. CHM.13710 Diluted or concentrated samples. In: Chemistry and toxicology checklist. April 2014:15.
3. College of American Pathologists. CHM.13720 Maximum dilution. In: Chemistry and toxicology checklist. April 2014:16.

David N. Alter, MD, DABCC
Clinical/Chemical Pathologist
Blood Bank Medical Director
Clinical Professor of Pathology
College of Human Medicine
Michigan State University
Spectrum Health Regional Laboratory
Grand Rapids, Mich.
Vice Chair, CAP Chemistry Resource Committee

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