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. 2017 Oct 23;38(1):67–70. doi: 10.3343/alm.2018.38.1.67

Effect of Accreditation on the Accuracy of Diagnostic Hematologic Tests: Standard Deviation Index Analysis

Young Ahn Yoon 1, Mi-Ae Jang 2, Ji Sung Lee 3, Won-Ki Min 4, Kye Chul Kwon 5, Yong-Wha Lee 2,✉, You Kyoung Lee 2,✉
PMCID: PMC5700151  PMID: 29071823

Dear Editor,

Thorough quality management is paramount because diagnostic tests play an important role in medical decisions and can involve a complex, multistep process, from sampling to reporting the test results. In general, the reliability of a diagnostic test is based on two factors: diagnostic product standardization and practice standardization. While diagnostic product standardization is established on a legal basis with administrative assistance, practice standardization is less well established and can, to a large extent, depend on the private sector. In Korea, this private sector involvement is mediated through the Korean Laboratory Accreditation Program (KLAP).

KLAP was established in 1999 and instituted by Korean Society for Laboratory Medicine (KSLM) [1]. KLAP conducts document screening and on-site inspections to assess test results and compliance with practice standardization.

The Korean external quality assessment scheme (KEQAS) is a proficiency testing program run by the Korean Association of Quality Assurance for Clinical Laboratory [2]. KEQAS distributes the same material to all participating laboratories and statistically analyzes the results of the measurements. This permits the analytical accuracy of the test results of individual laboratories to be monitored and objectively measured.

Laboratories that participate only in the KEQAS are designated as basically-standardized laboratories (BSL). A highly-standardized laboratory (HSL) is a laboratory that participates simultaneously in KEQAS and KLAP and obtains a certificate of accreditation.

Recently, we reported the results of an accreditation analysis of clinical chemistry tests in clinical laboratories [3]. We concluded that practice standardization is strongly associated with the accuracy of clinical chemistry test results. Here, we extended the findings by analyzing the impact of standardization on diagnostic hematology test results.

Five items, Hb, Hct, red blood cell (RBC), white blood cell (WBC), and platelet count, were analyzed. The analyses involved results obtained from 30,616 samples over a 9-year period (2005–2013). The Hct data were from an 8-year period (2006–2013). The standard deviation index (SDI), defined as: (measured value of the institution - average of the participating institutions)/standard deviation of the participating institutions, was used for evaluation. The higher the absolute SDI value, the more inferior the results, as they are less similar to the average of the participating institutions.

First, we compared the SDI of all five items according to whether laboratories were KLAP-certified using diagnostic blood test result data from the 9-year KEQAS. SDI mean values were compared using the Student's t-test; significance was assigned at P<0.05. Compared with non-KLAP accredited laboratories, accredited laboratories showed significantly lower geometric means for all 9-year SDI in Hb, 3-year SDI in Hct and WBCs, 5-year SDI in RBCs, and 2-year SDI in platelets (all P<0.05; Table 1).

Table 1. Comparison of standard deviation index between accredited and non-accredited laboratories.

Year Non-accredited laboratories Accredited laboratories P‡
N* SDI† 95% CI N SDI 95% CI
Hb 2005 290 0.73 [0.68 0.78] 172 0.52 [0.47 0.57] < 0.01
2006 381 0.85 [0.79 0.92] 180 0.68 [0.62 0.74] < 0.01
2007 372 0.66 [0.61 0.72] 189 0.55 [0.50 0.60] < 0.01
2008 450 0.71 [0.66 0.75] 201 0.58 [0.54 0.62] < 0.01
2009 652 0.85 [0.81 0.89] 215 0.62 [0.58 0.65] < 0.01
2010 778 0.71 [0.67 0.74] 230 0.49 [0.45 0.52] < 0.01
2011 850 0.93 [0.89 0.97] 242 0.62 [0.58 0.66] < 0.01
2012 911 0.66 [0.63 0.69] 255 0.47 [0.43 0.50] < 0.01
2013 1025 0.82 [0.78 0.85] 261 0.56 [0.52 0.60] < 0.01
Hct 2006 381 0.77 [0.72 0.82] 180 0.77 [0.71 0.84] 0.91
2007 372 0.70 [0.66 0.75] 189 0.74 [0.68 0.80] 0.38
2008 450 0.74 [0.70 0.79] 201 0.66 [0.61 0.71] < 0.01
2009 652 0.71 [0.67 0.74] 215 0.79 [0.73 0.86] 0.02
2010 778 0.66 [0.63 0.69] 230 0.71 [0.65 0.77] 0.20
2011 850 0.71 [0.67 0.74] 242 0.94 [0.87 1.02] < 0.01
2012 911 0.69 [0.66 0.72] 255 0.84 [0.79 0.89] < 0.01
2013 1025 0.74 [0.71 0.77] 261 0.79 [0.73 0.86] 0.19
RBC 2005 290 0.72 [0.67 0.78] 172 0.52 [0.48 0.57] < 0.01
2006 381 0.80 [0.74 0.86] 180 0.73 [0.68 0.79] 0.12
2007 372 0.69 [0.64 0.74] 189 0.63 [0.59 0.68] 0.13
2008 450 0.68 [0.64 0.73] 201 0.67 [0.63 0.72] 0.78
2009 652 0.78 [0.74 0.83] 215 0.64 [0.59 0.69] < 0.01
2010 778 0.68 [0.64 0.71] 230 0.53 [0.49 0.58] < 0.01
2011 850 0.78 [0.74 0.82] 242 0.68 [0.62 0.74] < 0.01
2012 911 0.20 [0.19 0.22] 255 0.16 [0.15 0.18] < 0.01
2013 1025 0.82 [0.79 0.86] 261 0.60 [0.57 0.64] < 0.00
WBC 2005 290 0.65 [0.60 0.71] 172 0.59 [0.54 0.65] 0.13
2006 381 0.86 [0.79 0.94] 180 0.77 [0.69 0.85] 0.09
2007 372 0.67 [0.62 0.73] 189 0.65 [0.59 0.72] 0.67
2008 450 0.67 [0.62 0.72] 201 0.60 [0.56 0.65] 0.05
2009 652 0.89 [0.84 0.95] 215 0.81 [0.74 0.88] 0.07
2010 778 0.68 [0.64 0.71] 230 0.60 [0.56 0.65] 0.01
2011 850 0.84 [0.80 0.88] 242 0.73 [0.67 0.78] < 0.01
2012 911 0.43 [0.41 0.45] 255 0.37 [0.35 0.39] < 0.01
2013 1025 0.80 [0.77 0.84] 261 0.74 [0.70 0.79] 0.04
Platelet 2005 290 0.68 [0.63 0.73] 172 0.71 [0.66 0.76] 0.44
2006 381 0.76 [0.71 0.81] 180 0.84 [0.77 0.91] 0.08
2007 372 0.68 [0.64 0.73] 189 0.75 [0.69 0.81] 0.07
2008 450 0.67 [0.63 0.71] 201 0.77 [0.73 0.82] < 0.01
2009 652 0.73 [0.69 0.76] 215 0.73 [0.68 0.79] 0.86
2010 778 0.67 [0.64 0.71] 230 0.86 [0.80 0.92] < 0.01
2011 850 0.72 [0.68 0.75] 242 0.78 [0.72 0.85] 0.07
2012 911 0.68 [0.65 0.71] 255 0.72 [0.67 0.76] 0.25
2013 1025 0.75 [0.72 0.78] 261 0.70 [0.65 0.75] 0.09
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*Number of laboratories; †Values represent the geometric mean; ‡P-value by Student's t-test using the log-transformed values.

Abbreviations: SDI, standard deviation index; RBC, red blood cell; WBC, white blood cell; CI, confidence interval; Hb, hemoglobin; Hct, hematocrit.

Second, the SDI of Hb test results was analyzed statistically in KEQAS according to KLAP certification status and institutional type. Participating institutes were categorized as general hospitals with>100 beds, hospitals with 30-99 beds, and clinics with <30 beds. For the 9-year Hb test data, laboratories with KLAP accreditation showed significantly lower geometric means of 8-year SDI in general hospitals, 1-year SDI in hospitals, and 7-year SDI in clinics compared with laboratories without KLAP accreditation (all P<0.05; Table 2).

Table 2. Comparison of hemoglobin standard deviation index between accredited and non-accredited laboratories by institutional type.

Year General Hospital P‡ Hospital P Clinic P
Non-accredited laboratories Accredited laboratories Non-accredited laboratories Accredited laboratories Non-accredited laboratories Accredited laboratories
N* SDI N SDI N SDI N SDI N SDI N SDI
2005 112 0.68 156 0.53 0.00 78 0.80 5 0.62 0.48 56 0.67 11 0.40 < 0.01
2006 121 0.77 163 0.67 0.08 109 1.00 5 1.15 0.76 102 0.74 12 0.56 0.24
2007 113 0.60 171 0.55 0.31 108 0.75 6 0.78 0.94 102 0.60 12 0.46 0.27
2008 115 0.68 183 0.58 0.02 142 0.77 6 0.81 0.85 135 0.63 12 0.50 0.03
2009 125 0.80 194 0.63 0.00 241 0.87 8 0.53 0.09 207 0.85 13 0.52 0.01
2010 123 0.63 203 0.49 0.00 306 0.73 11 0.47 0.02 267 0.72 15 0.42 < 0.01
2011 124 0.77 210 0.61 0.00 341 0.99 14 0.95 0.87 296 0.93 17 0.55 < 0.01
2012 120 0.54 217 0.46 0.04 380 0.71 17 0.59 0.23 322 0.67 20 0.41 < 0.01
2013 151 0.74 219 0.55 0.00 433 0.85 20 0.70 0.11 343 0.84 21 0.51 < 0.01
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*Number of laboratories; †Values representthe geometric mean; ‡P-value by Student's t-test using the log-transformed values.

Abbreviation: see Table 1.

Clinical chemistry results were reported to be more accurate and reliable in KLAP-accredited laboratories [3]. However, the present diagnostic hematology results show that practice standardization did not significantly affect test results, except for the Hb test item. There are several differences between diagnostic hematology and clinical chemistry tests [4,5,6,7]. Most diagnostic hematology instruments use flow cytometry cell counting, but use spectrophotometry to measure Hb values. Spectrophotometry is widely used in clinical chemistry, while flow cytometry exhibits high precision with low uncertainty. In other words, product standardization, conducted prior to practice standardization, is already excellent; thus, practice standardization will have little effect on the results. It can be assumed that only Hb values are meaningful for all the analysis years, while the other test items exhibit varying significance depending on year. In conclusion, diagnostic test practice standardization is useful for obtaining more reliable and accurate test results; however, the degree of improvement will depend on the particular test measurement principles in diagnostic hematology.

Acknowledgements

We wish to thank the Korean Association of External Quality Assessment Service and the Laboratory Medicine Foundation for providing the data used in this study. This work was supported by the Soonchunhyang University Research Fund and by the Korea Centers for Disease Control and Prevention, Korea (2014-187).

Footnotes

Authors' Disclosures of Potential Conflicts of Interest: No potential conflicts of interest relevant to this article are reported.

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