Comparison of pooled fresh frozen serum to proficiency testing material in College of American Pathologists surveys: Cortisol and immunoglobulin E

Darryl Erik Palmer-Toy, Edward Wang, William E. Winter, Steven J. Soldin, George G. Klee, Joan H. Howanitz, Ronald J. Elin

Research output: Contribution to journalReview article

13 Scopus citations

Abstract

Context.-The College of American Pathologists (CAP) provides proficiency testing (PT) surveys to laboratories around the world. Objectives.-To compare diagnostic assay methods for serum/plasma cortisol and immunoglobulin (Ig) E in terms of their bias and precision, to determine how well CAP PT specimens simulate human serum, and to reassess proficiency test grading criteria in light of these findings. Design.-A participant-blinded, prospective trial. One vial of pooled fresh frozen serum (FFS) and 4 different admixtures of PT material (PTM) were sent to laboratories participating in PT surveys. Participants.-Laboratories providing cortisol (>1000) or IgE (>230) results among the subscribers to the CAP surveys, Ligand (General) 2003, set K/KN-A and Chemistry 2003, set C-C. Main Outcome Measures.-The main outcome measures were (1) bias among laboratories using the same method (peer groups), defined relative to the median of method means (MedMM); (2) imprecision as measured by the SD and coefficient of variation (CV) about each method mean; and (3) total error across laboratories for the FFS cortisol results, defined as [Bias Relative to Reference Method] + 2 SD. Results.-Cortisol method biases, relative to MedMM, ranged from -22% to 9% for the FFS challenge and from -24% to 36% for comparable PTM challenges. The method biases, relative to the reference method, ranged from -3% to 19% for the FFS challenge. The cortisol method CVs ranged from 4.2% to 13.6% for the FFS challenge and from 4.7% to 12.7% for comparable PTM challenges. Total error across laboratories ranged from 1.4 to 6.9 μg/dL (39 to 190 nmol/L) for the FFS challenge. Immunoglobulin E method biases, relative to MedMM, ranged from -8% to 9% for the FFS challenge and from -7% to 5% for comparable PTM challenges. The IgE method CVs ranged from 3.6% to 6.7% for the FFS challenge and from 3.4% to 9.8% for comparable PTM challenges. Conclusions.-The bias for cortisol results was less with FFS than with PTM, but imprecision was comparable. The FFS MedMM was 8.5% higher than the reference value. Fresh frozen serum and PTM bias and imprecision for IgE methods were each less than 10%. Because some of the methods demonstrated greater bias when analyzing PTM than FFS, peer group grading of both these analytes is appropriate.

Original languageEnglish (US)
Pages (from-to)305-309
Number of pages5
JournalArchives of Pathology and Laboratory Medicine
Volume129
Issue number3
StatePublished - Mar 1 2005

ASJC Scopus subject areas

  • Pathology and Forensic Medicine
  • Medical Laboratory Technology

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    Palmer-Toy, D. E., Wang, E., Winter, W. E., Soldin, S. J., Klee, G. G., Howanitz, J. H., & Elin, R. J. (2005). Comparison of pooled fresh frozen serum to proficiency testing material in College of American Pathologists surveys: Cortisol and immunoglobulin E. Archives of Pathology and Laboratory Medicine, 129(3), 305-309.