Send to

Choose Destination
Arch Pathol Lab Med. 2005 Mar;129(3):305-9.

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

Author information

Department of Pathology, Massachusetts General Hospital and Harvard Partners Center for Genetics and Genomics, Boston, Mass, USA.



The College of American Pathologists (CAP) provides proficiency testing (PT) surveys to laboratories around the world.


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.


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.


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.


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.


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 microg/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.


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.

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Allen Press, Inc.
Loading ...
Support Center