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pISSN 2950-9114 eISSN 2950-9122
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Original Article

Lab Med Qual Assur 2022; 44(2): 88-98

Published online June 30, 2022


Copyright © Korean Association of External Quality Assessment Service.

Establishment of Critical Difference for Diagnostic Immunoassays

Shinae Yu1 , Soo Young Moon2 , Kyung-Hwa Shin3 , Sun Min Lee4 , Chul Min Park5 , and Kyung Ran Jun1

1Department of Laboratory Medicine, Inje University Haeundae Paik Hospital, Inje University College of Medicine, Busan; 2Department of Laboratory Medicine, Dongguk University Ilsan Hospital, Goyang; 3Department of Laboratory Medicine, Pusan National University Hospital, Busan; 4Department of Laboratory Medicine, Pusan National University Yangsan Hospital, Yangsan; 5Department of Laboratory Medicine, Dongnam Institute of Radiological & Medical Sciences, Busan, Korea

Correspondence to:Kyung Ran Jun
Department of Laboratory Medicine, Inje University Haeundae Paik Hospital, Inje University College of Medicine, 875 Haeun-daero, Haeundae-gu, Busan 48108, Korea
Tel +82-51-797-3191
E-mail jun@paik.ac.kr

Received: December 22, 2021; Revised: January 26, 2022; Accepted: February 10, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background: Critical difference (CD) is a significant difference between sequential laboratory results in a patient and is a major parameter for comparative evaluation of quantitative clinical laboratory tests, and how significant the difference is should be set by the laboratory itself. In this study, we established the criteria for CD that can be referenced in each laboratory for diagnostic immunoassays.
Methods: We targeted 17 major diagnostic immunoassays as follows: alphafetoprotein (AFP), cancer antigen 125 (CA125), cancer antigen 15-3 (CA15-3), cancer antigen 19-9 (CA19-9), carcinoembryonic antigen (CEA), prostatespecific antigen (PSA), free PSA, tri-iodothyronine (T3), thyroxine (T4), free T4, thyroglobulin, thyroid-stimulating hormone (TSH), estradiol (E2), folliclestimulating hormone (FSH), luteinizing hormone (LH), testosterone, and prolactin. According to Clinical and Laboratory Standards Institute EP31, we investigated acceptance criteria for CD based on clinical outcomes, clinician’s questionnaire, biological variation, published professional recommendations, goals set by accrediting agencies, and general capability in the Korean Association of External Quality Assessment Service.
Results: We selected the acceptance criteria for CD as follows: 6.0% for total PSA and TSH based on well-designed clinical study’s outcomes; 20.0% for AFP, CA19-9, CEA, and free PSA, 10.0% for T3, 14.3% for T4, 12.5% for free T4, 16.9% for thyroglobulin, 22.2% for E2, 22.9% for FSH, 20.0% for LH, 10.0% for testosterone, and 25.0% for prolactin based on clinician’s questionnaire; 8.4% for CA125 and 10.2% for CA15-3 based on general capability.
Conclusions: Applying the acceptance criteria for CD from this study may help assess the comparability of the quantitative tests in routine laboratory practice.

Keywords: Critical difference, Tumor biomarkers, Thyroid function tests, Estradiol, Follicle stimulating hormone, Luteinizing hormone, Testosterone, Prolactin

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