원저 Lab Med Online Vol. 3, No. 4: 221-22, October 2013 임상화학 CAPILLARYS 2 FLEX Piercing HbA 1c 검사성능평가 Performance Evaluation of the CAPILLARYS 2 FLEX Piercing Analyzer for HbA1c Determination 전용범 1 한민제 1 이경훈 1 장호은 2 박경운 2 송정한 2 Yongbum Jeon, M.D. 1, Minje Han, M.D. 1, Kyunghoon Lee, M.D. 1, Ho Eun Chang, M.T. 2, Kyoung Un Park, M.D. 2, Junghan Song, M.D. 2 1 서울대학교병원진단검사의학과, 2 분당서울대학교병원진단검사의학과 Department of Laboratory Medicine 1, Seoul National University Hospital, Seoul; Department of Laboratory Medicine 2, Seoul National University Bundang Hospital, Seongnam, Korea Background: The hemoglobin A1c (HbA1c) level is widely used to monitor glycemic control in diabetes mellitus patients, and various methods are used for its determination. The CAPILLARYS 2 FLEX Piercing (Sebia) is a fully automated, high-throughput glycohemoglobin (HbA1c) analyzer based on capillary electrophoresis. Methods: The analytical performance of the CAPILLARYS 2 FLEX Piercing analyzer was evaluated for its precision, linearity, correlation with the Variant II Turbo (Bio-Rad Laboratories, Inc.) analyzer, and its vulnerability to interference by carbamylated hemoglobin. We also investigated its agreement with National Glycohemoglobin Standardization Program (NGSP) targets. All evaluations were performed according to CLSI guidelines EP0, EP0, and EP09. Results: The coefficients of variation (CVs) for within-run and total imprecision were 1.7% and 1.8% at low concentrations and 1.2% and 1.3% at high concentrations, respectively. Linearity was excellent, with R 2 =0.9882 in the range of.13-13.83%; these results highly correlated with those produced by Variant II Turbo (R 2 =0.9978). The 9% confidence interval (for differences from the NGSP target) was -0.318-0.3343%. No significant interference of carbamylated hemoglobin was noted. Conclusions: The CAPILLARYS 2 FLEX Piercing analyzer showed excellent precision and linearity. Its results correlated with those obtained by the Variant II Turbo analyzer, and were agreement with the NGSP target. Therefore, its analytical performance is satisfactory for diabetes diagnosis and treatment monitoring. Key Words: Hemoglobin A1c (HbA1c), Capillary electrophoresis, Diabetes 서론 당뇨병의유병률은세계적으로급속히증가하는추세로, 세계 보건기구 (WHO) 는전세계당뇨병인구가 202 년에는 3 억 3 천만에 Corresponding author: Junghan Song Department of Laboratory Medicine, Seoul National University Bundang Hospital, 82 Gumi-ro 173 beon-gil, Bundang-gu, Seongnam 43-707, Korea Tel: +82-31-787-791, FAX: +82-31-787-401, E-mail: songjhcp@snu.ac.kr Received: October 9, 2012 Revision received: March 11, 2013 Accepted: March 12, 2013 This article is available from http://www.labmedonline.org 2013, Laboratory Medicine Online This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 육박할것으로추산하였고 [1], 우리나라국민건강영양조사결과에의하면 30세이상성인의당뇨병유병률은 2001년 8.%, 200년 9.1%, 2009년 9.% 로사회경제적인발전에따라당뇨병인구가늘어나고있다 [2]. 당뇨병의진단및관리를위한추적관찰에는혈당및당화혈색소가사용된다. 약 30년전에당뇨병환자들에서처음규명된혈중 hemoglobin A 1c (HbA 1c) 는최근 2-3개월간의평균혈당치를반영하므로장기간혈당상태파악에가장신뢰도가높은지표로서, 당뇨병의치료효과판정및합병증의조절과예방을관찰하는데사용된다 [3]. 2007년미국당뇨병학회 (American Diabetes Association, ADA), European Association for the Study of Diabetes (EASD), International Diabetes Federation (IDF), International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) 가발표한합의문에서 HbA 1c 의전세계적인표준화 (standardization) 의필요성이강 eissn 2093-338 www.labmedonline.org 221
조되었고, IFCC 참고방법만이표준화를위한유일한기반임을인정했다 [4]. 최근미국당뇨병학회는 2010년당뇨병의진단및고위험군선정기준에 HbA 1c 농도를포함시켰다 []. 이에의하면 National Glycohemoglobin Standardization Program (NGSP) 의인증을받고 Diabetes Control and Complications Trial (DCCT) 참고방법에추적성 (traceability) 을갖고있는검사법으로측정한 HbA 1c 결과가.% 이상이면당뇨병으로진단할수있고,.7-.4% 인경우는당뇨병의고위험군으로판정할수있다. 또한제조사는 IFCC 참고방법에대해추적성을보여주어야한다. 따라서당뇨병환자들의추적및진단검사로서 HbA1c의중요성을감안할때외래진료를받는환자들의경우당일진료전검사에대해신속하고정확한결과를산출하는것이점점더요구된다. HbA 1c 의측정법은크게 3가지가있는데검사원리에따라이온교환고성능액체크로마토그래피 (ion-exchange high performance liquid chromatography, HPLC), 친화크로마토그래피 (affinity chromatography), 그리고면역측정법 (immunoassay) 으로나눌수있다. 이외에도전기영동법 (electrophoresis), 등전점측정법 (isoelectric focusing), 비색법, 분광법등과같은다양한측정법이이용되고있다. 최근에개발된 CAPILLARYS 2 FLEX Piercing 자동분석기 (Sebia, Norcross, GA) 는모세관전기영동 (capillary electrophoresis) 을이용한 HbA 1c 자동분석장비로이에대한분석능력및유용성에대한평가는국내에서아직보고된바없다. 이에정밀도, 직선성, 상관성, NGSP의이차표준검사실과의일치도를평가함으로서임상검사실에서의유용성을확인하고자하였다. 재료및방법 1. 장비및시약 CAPILLARYS 2 FLEX Piercing (Sebia) 는 8개의모세관튜브를장착한장비로모세관전기영동법을이용하여전처리가필요없이전혈검체의연속적장착이가능하다. 검체는 EDTA 신선전혈검체가이용되며검사에필요한최소검체량은 100 μl이다. 상관성평가용장비로는 Varinat II Turbo (Bio-Rad Laboratories, Inc., USA) HPLC 장비를사용하였다. 검사는각제조회사의지침에따라시행되었다. 모두제조사전용키트의시약을사용하였고, 또한동일한로트를사용하였다. 2. 정밀도 (Precision) 정밀도는 Clinical and Laboratory Standard Institute (CLSI) EP0-A2 지침에따라, 낮은농도와높은농도의 HbA 1c 정도관리물질을각각 20일간하루에 2회씩반복측정하여평가하였다 []. 검 사내정밀도, 검사일간정밀도와총정밀도의변이계수를 CLSI EP0-A2에서제시한방법으로구하였다. 3. 직선성 (Linearity) 직선성은 CLSI EP0-A에준하여평가하였다 [7]. CAPILLARYS 2 FLEX Piercing 장비에서,.00% 의낮은 HbA 1c 농도를보이는검체와 13.33% 의높은농도를보이는검체를각각 0:4, 1:3, 2:2, 3:1, 4:0 으로혼합하여조제한 개농도의검체를각각 4회씩반복하여측정하였다. 선형회귀분석을이용하여회귀방정식과결정계수 (R 2 ) 을구하였다. 4. 상관성 (Correlation) 상관성평가는 CLSI EP09-A2 지침에따라수행하였다 [8]. HbA 1c 농도가 4.7-13.% 인환자검체 40개를선정하여 Variant II Turbo와 CAPILLARYS 2 FLEX Piercing 장비로각각두차례반복측정하였고, Passing-Bablok 회귀분석으로상관성을평가하였다. Passing- Bablok 회귀분석에의한 Pearson 상관계수 (r) 를구하고상관방정식과오차도표를그렸다.. Carbamylated hemoglobin에의한간섭효과평가요독증환자의경우, 요소로부터유래된이소시아네이트가헤모글로빈과반응하여 carbamylated hemoglobin을생성하는데, 이것이 HbA 1c 에대해간섭효과를나타낸다 [9, 10]. 이온교환크로마토그래피에기반한 HPLC 방법과는달리, 모세관전기영동방법에서는 carbamylated hemoglobin의간섭효과가없는것으로알려져있다 [11]. 본연구에서는높은 blood urea nitrogen (BUN) 농도 (7-1 mg/dl) 를가진 2개의검체를이용하여, 역시간섭효과가없는면역측정법을사용하는 Cobas Integra 800 (Roche Diagnostics, Basel, Switzerland) 으로측정한결과와비교하였고, 기존문헌의방법대로 CAPILLARYS 2 FLEX Piercing 과 Cobas Integra 800 간의측정값차이를혈청요소농도에대한함수로표시한회귀방정식의상관성을분석하였다 [10].. NGSP 표준검사실과의일치도평가 (Agreement) 표준검사실결과와의일치도를평가하기위하여, 미국 NGSP에서실시하는검사실인증프로그램용 40개검체를이용하였다. 2012년 2월 NGSP 이차표준검사실 (secondary reference lab) 에서측정후 -70 C에서냉동보관된검체를 2012년 월 CAPILLARYS 2 FLEX Piercing으로 2회반복측정하였고, 이들검사값과 NGSP 측정값과의일치도평가를위하여 Passing-Bablok 회귀분석과 Bland-Altman agreement 분석을실시하였다. 222 www.labmedonline.org
7. 통계분석통계분석은 Microsoft Excel 2010 (Microsoft Corporation, Redmond, WA, USA) 과 MedCalc version 12.2.1 (MedCalc Software, Mariakerke, Belgium) 프로그램을사용하였다. 결과낮은농도와높은농도의정도관리물질을대상으로측정한검사내정밀도의변이계수는각각 1.7% 와 1.2% 이었고, 검사일간정밀도의변이계수는각각 0.% 와 0.% 이었으며, 총정밀도의변이계수는각각 1.8% 과 1.3% 이었다 (Table 1). CAPILLARYS 2 FLEX Piercing 을이용해낮은농도와높은농도의환자검체로조제한 가지농도의검체를 4회반복측정한결과,.00-13.33% 의 HbA 1c 농도범위에서 R 2 = 0.9882의우수한직선 성을보였다 (Fig. 1). Variant II Turbo (x) 와 CAPILLARYS 2 FLEX Piercing (y) 에서동시에중복측정한 HbA 1c 농도는 4.7-13.% 범위에서우수한상관성을보였고 (R 2 = 0.9978), Passing-Bablok 회귀분석을시행한결과 y =1.000x + 0.00의관계를나타내었다 (Fig. 2). 높은요소농도를가진검체로 CAPILLARYS 2 FLEX Piercing 과 Cobas Integra 800 간의측정값차이 (y) 를혈청요소농도 (x) 에대한함수로표시했을때, 선형회귀분석의결과 y =-0.008x-0.018의관계를나타내었다. 혈청요소농도의변화에따른두장비간의유의한차이는관찰되지않았다 (R 2 = 0.07, P = 0.210) (Fig. 3). NGSP 이차표준검사실에서측정한결과와 CAPILLARYS 2 FLEX Piercing 으로측정한결과간의 Bland-Altman 일치도를평가한결과, NGSP 목표치에대한차이의평균과표준편차는 -0.0138± 0.1721% 였고, 9% 신뢰구간은 -0.318~0.3343% 였다 (Fig. 4). 14 13 Scatter Plot y = 0.997x-0.337 R 2 = 0.988 고찰 Measured (%) 12 11 10 9 8 7 4 4 7 8 9 10 11 12 13 14 Assigned (%) Fig. 1. Linearity of HbA1c values using the CAPILLARYS 2 FLEX Piercing analyzer. 당화혈색소측정을임상검사실에서도입한것은 1977년경부터이며 [12], 이후당화혈색소측정을위한많은방법들이개발되었고대부분의방법들이전하의차이 (HPLC법) 나구조의차이 ( 친화크로마토그래피, 면역측정법 ) 를이용하는것이었다. HbA 1c 는당뇨병의치료효과를판정하는데중요한지표로널리이용되어왔고, 최근에는당뇨병의진단및고위험군선정기준에 HbA 1c 이포함되었다 []. 따라서당뇨병의정확한치료및진단을위해서는모든검사장비및시약이동일한 HbA 1c 결과를제공하여야하는, 즉검사결과의표준화가선행되어야한다. 최근미국의 NGSP, 유럽의 IFCC, 일본의 Japanese Diabetes Society (JDS)/Japanese Society of Clinical Chemistry (JSCC) 등에서는각각의국가별로당화혈색소의일치화 (harmonization) 를수행해왔으나, 이들방법간에는검사결과에상당한차이를보이고있었다 [13, 14]. IFCC에서는 Table 1. Imprecision of the CAPILLARYS 2 FLEX Piercing analyzer Capillaries Within-run imprecision, CV (%) Between-day imprecision, CV (%) Total imprecision, CV (%) Low level (HbA1c.74%) High level (HbA1c 8.8%) Low level (HbA1c.74%) High level (HbA1c 8.8%) Low level (HbA1c.74%) High level (HbA1c 8.8%) 1 1. 1.1 0.3 0.7 2.0 1.3 2 0.8 0.7 0.0 0.4 1.1 0.9 3 1.0 0.9 0.8 0.7 1.3 1.1 4 1.0 0.9 0.8 0.7 1.4 1.2 1. 0.8 0. 0. 1.7 1.1 1.1 0.8 0.7 0.7 1.3 1.1 7 0.9 1.0 0.3 0.4 1.1 1.1 8 1.8 1.1 0.0 1.2 1.9 1.8 Total 1.7 1.2 0. 0. 1.8 1.3 www.labmedonline.org 223
14 Scatter plot with Passing and Bablok Fit Bias plot CAPILLARYS 2 FLEX piercing (%) 13 12 11 10 9 8 7 Identity Passing and Bablok fit (y=1.000x+0.00) 9% CI bands 4 4 7 8 9 10 11 12 13 14 Bias (%) 4 3 2 1 0-1 -2 +1.9 SD 3.4 Mean 0. -1.9 SD -2.2-3 4 7 8 9 10 11 12 13 14 1 1 Variant ІІ Turbo (%) Variant ІІ Turbo (%) Fig. 2. Comparison of HbA1c levels measured using the Variant II Turbo analyzer (comparative) and the CAPILLARYS 2 FLEX Piercing analyzer (test). Absolute difference of HbA1C ( CAPILLARYS-Integra) (%) 0.4 0.2 0.0-0.2-0.4-0. y = -0.008x-0.018 R 2 = 0.07 P=0.210-0.8 20 30 40 0 0 Fig. 3. Relationship between serum urea concentrations and the absolute difference in HbA1c percentages obtained using the 2 methods. 199 년부터 HbA 1c 측정의국제적표준화를위한실무위원회를만 들었으며, 1 차표준물질의제조뿐만아니라 HPLC- 질량분석기 (mass spectrometry) 법이나 HPLC- 모세관전기영동법을이용하는 참고방법을확정하였다 [1, 1]. Serum urea concentration (mmol/l) 현재 IFCC 의참고방법은헤모글로빈을 endoproteinase Glu-C 로처리하여베타체인의 N 말단을절단하고 HPLC 로당화헥사펩 타이드와비당화헥사펩타이드를분리하는방법이다. 헥사펩타이 드는 HPLC- 질량분석기법또는 HPLC- 모세관전기영동법으로정량 하며이두가지방법이동일하게참고방법으로사용되며같은성 능을가지는것으로인정되고있다 [14]. 저자들은 IFCC 참고방법의 하나인 HPLC/CE법을사용하는 CAPILLARYS 2 FLEX Piercing 기기의분석능력을평가하였다. 본연구에서저자들은 CAPILLARYS 2 FLEX Piercing 기기의정밀도, 직선성을통해분석능을평가하였고, NGSP 인증을받아현재본원에서사용중인 Variant II Turbo와의상관성을평가하였고, NGSP의이차참고검사실과의일치도를평가하였다. 미국임상화학회 (National Academy of Clinical Biochemistry, NACB) 의당뇨병의진단과관리를위한임상검사지침과권고안 (Laboratory medicine practice guidelines, LMPG) 에의하면 HbA1c의측정에있어바람직한정밀도는검사실내 CV 2% 미만, 검사실간 CV 3.% 미만으로권고하고있다 [17]. 본연구에서의정밀도검사는총정밀도가 1.3-1.8% 으로기존에보고된다른기기보다작거나비슷한변이계수수치를보였고 [18-20], 검사내정밀도와총정밀도는모두 2% 미만을유지하고있어국제기관들의권고안을만족하였다. CAPILLARYS 2 FLEX Piercing (y) 장비의직선성은상관계수 (R 2 ) 값이 0.9882로우수하였으며, HPLC법인 Variant II Turbo (x) 와비교할때는 y =1.000x + 0.00, R 2 = 0.9978으로비례오차 (proportional error) 와상존오차 (constant error) 가거의없이우수한상관성을보였다. 1 mmol/l의 urea 당 0.03% 의 carbamylated hemoglobin이생성된다고알려져있으며, 면역검사법은 carbamylated hemoglobin의간섭효과가없는것으로알려져있다 [11]. 7-1 mg/dl의 BUN을가진검체를이용한간섭효과검사에서는 1.7-3.% 의 carbamylated hemoglobin 이영향이있을것으로예상되지만, 높은요소농도를가진검체에서동질면역검사법의 Cobas Integra 800과 CAPILLARYS 2 FLEX Piercing 을비교했을때통계적으로유의한차이가없는결과를보여, 알려진바와같이모세관 224 www.labmedonline.org
CAPILLARYS 2 FLEX piercing (%) 11 10 9 8 7 Scatter Plot with Passing and Bablok Fit Identity Passing and Bablok fit (y=0.947x+0.33) 9% CI bands I 검사실의경우 ±0.70% 이내, Level II 검사실의경우 ±0.7% 이내들어야인증을부여하고있다 [22]. 저자들의연구에서평가한 NGSP 목표치와의차이의 9% 신뢰구간은 -0.318~0.3343% 로 NGSP의 Level I 인증기준 (±0.70%) 에부합하였고, NGSP 이차표준검사실과우수한일치도를보였다. 결론적으로, CAPILLARYS 2 FLEX Piercing 은뛰어난정밀도와직선성및 NGSP 이차표준검사실과의우수한일치도를나타내었으므로, HbA 1c 분석을통한당뇨병의진단및치료효과의추적관찰을위해사용할수있는장비라고판단된다. 또한, 기존장비와의높은상관도를나타내므로임상검사실에서기존장비를대체할만한성능을나타낼수있을것이다. CAPILLARYS mean-ngsp mean (%) 전기영동방법과마찬가지로 carbamylated hemoglobin 의간섭효 과는없었다. 이는당뇨병의흔한합병증인당뇨병성신증에의한 요독증환자에서정확한 HbA1c 의측정에필수적인요건이될것 이다. 4 4 7 8 9 10 11 NGSP target (%) 0.4 0.3 0.2 0.1 0.0-0.1-0.2-0.3-0.4 Bias Plot 9% CI of differences 0.3343 Mean -0.0138-0.318-0. 4 7 8 9 10 11 Average of Sebia mean and NGSP mean (%) Fig. 4. Assessment of agreement of HbA1c levels between the NGSP target and CAPILLARYS 2 FLEX Piercing analyzer. HbA 1c 의검사의정확도를평가하기위해서는 IFCC 참고방법으 로측정한참값을알고있고측정호환성이있는 (commutable) 물 질을이용하여평가대상장비로측정한후참값과의차이를분석 하는것이제일좋은방법이지만, 현실적으로 IFCC 참고방법으로 측정한물질을구하기에는어려움이있다. NGSP HbA 1c 값과 IFCC 값에서변환한 NGSP HbA 1c 값의호환성이인정되어있고 [21], 저자 의검사실이미국 NGSP 표준화인증프로그램에참여하고있으 므로표준화인증을위해사용된검체를이용하여검사의정확도 를간접적으로파악할수있었다. NGSP 인증에서는평가하려는 검사장비와이차표준검사실간의결과차이의 9% 신뢰구간 Level 요약 배경 : 헤모글로빈 A 1c (HbA 1c) 농도는당뇨병환자에서혈당조절을추적관찰하는데널리사용되고있으며, 측정시다양한방법이사용되고있다. CAPILLARYS 2 FLEX Piercing (Sebia) 은모세관전기영동에기초한완전자동화된 HbA1c 분석기로서, 저자들은장비의성능을평가하였다. 방법 : CAPILLARYS 2 FLEX Piercing 의분석능은정밀도, 직선성, Variant II Turbo (Bio-Rad Laboratories, Inc.) 와의상관성, carbamylated hemoglobin에의한간섭효과와, 미국 NGSP와의일치도를평가하였고, CLSI 가이드라인 EP0, EP0와 EP09에따라성능평가를수행하였다. 결과 : 정밀도의총변이계수는 1.3-1.8% 이었고, 직선성은.13-13.83% 의농도범위에서 R 2 = 0.9882였다. Variant II Turbo 와의상관성은 R 2 값이 0.9978이었으며, NSGP target과의차이의 9% 신뢰구간은 -0.318~0.3343% 이었다. Carbamylated hemoglobin에의한유의한간섭효과는없었다. 결론 : CAPILLARYS 2 FLEX Piercing 은뛰어난정밀도와직선성및 NGSP 이차표준검사실과의우수한일치도를나타내었으므로, HbA 1c 분석을통한당뇨병의진단및치료효과의추적관찰을위해효율적으로사용할수있는장비라고판단된다. 감사의글 이논문은분당서울대학교병원위탁연구비 (0-2012-089) 지원에의해이루어진것임. REFERENCES 1. World Health Organization (200) Definition and diagnosis of diabe- www.labmedonline.org 22
tes mellitus and intermediate hyperglycemia. Report of a WHO/IDF consultation. WHO, Geneva. 2. Korea Health Statistics 2009: Korea National Health and Nutrition Examination Survey. 3. Bunn HF, Gabbay KH, Gallop PM. The glycosylation of hemoglobin: relevance to diabetes mellitus. Science 1978;200:21-7. 4. Trevino G. Consensus statement on the Worldwide Standardization of the Hemoglobin A1c Measurement: the American Diabetes Association, European Association for the Study of Diabetes, International Federation of Clinical Chemistry and Laboratory Medicine, and the International Diabetes Federation: response to the Consensus Committee. Diabetes Care 2007;30:e141.. American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care 2010;34(S1):S2-9.. Clinical and Laboratory Standards Institute. Evaluation of precision performance of quantitative measurement methods; approved guideline. EP0-A2. Wayne, PA: National Committee for Clinical Laboratory Standards, 2004. 7. Clinical and Laboratory Standards Institute. Evaluation of the linearity of quantitative measurement procedures: a statistical approach; approved guideline. EP0-A. Wayne, PA: National Committee for Clinical Laboratory Standards, 2003. 8. Clinical and Laboratory Standards Institute. Method comparison and bias estimation using patient samples; approved guideline. EP09-A2- IR. Wayne, PA: National Committee for Clinical Laboratory Standards, 2010. 9. Lamb E, Dawnay A. Glycated haemoglobin measurement in uraemic patients. Ann Clin Biochem 1992;29:118-20. 10. Weykamp CW, Penders TJ, Siebelder CW, Muskiet FA, van der Slik W. Interference of carbamylated and acetylated hemoglobins in assays of glycohemoglobin by HPLC, electrophoresis, affinity chromatography and enzyme immunoassay. Clin Chem 1993;39:138-42. 11. Weykamp CW, Miedema K, de Haan T, Doelman CJ. Carbamylated hemoglobin interference in glycohemoglobin assays. Clin Chem 1999;4:438-40. 12. John WG, Mosca A, Weykamp C, Goodall I. HbA1c standardisation: history, science and politics. Clin Biochem Rev 2007;28:13-8. 13. Hoelzel W, Weykamp C, Jeppsson JO, Miedema K, Barr JR, Goodall I, et al. IFCC reference system for measurement of hemoglobin A1c in human blood and the national standardization schemes in the United States, Japan, and Sweden: a method-comparison study. Clin Chem 2004;0:1-74. 14. Weykamp C, John WG, Mosca A, Hoshino T, Little R, Jeppsson JO, et al. The IFCC reference measurement system for HbA1c: a -year progress report. Clin Chem 2008;4:240-8. 1. Mosca A, Goodall I, Hoshino T, Jeppsson JO, John WG, Little RR, et al. Global standardization of glycated hemoglobin measurement: the position of the IFCC Working Group. Clin Chem Lab Med 2007;4:1077-80. 1. Kaiser P, Akerboom T, Ohlendorf R, Reinauer H. Liquid chromatography-isotope dilution-mass spectrometry as a new basis for the reference measurement procedure for hemoglobin A1c determination. Clin Chem 2010;:70-4. 17. Sacks DB, Arnold M, et al. eds. Laboratory medicine practice guidelines: Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Washington, DC: National Academy of Clinical Biochemistry, 2011:2-30. 18. Park HD, Kim HJ, Kim MS, Lee SY, Kim JW. Evaluation of hemoglobin A1c on the Cobas Integra 800 immunoassay and Tosoh HLC-723 G8 HPLC analyzer. J Lab Med Qual Assur 2009;31:239-4. 19. Kim T, Kim S, Chang HE, Song SH, Park KU, Song J, et al. Performance evaluation of HbA1c test on the Toshiba 200FR NEO using autolab HbA1c reagent. J Lab Med Qual Assur 2010;32:217-23. 20. Choi Q, Han M, Chang HE, Song SH, Park KU, Song J. Performance evaluation of the ADAMS A1c HA-8180 analyzer for HbA1c. J Lab Med Qual Assur 2012;34:2-30. 21. Paisooksantivatana K, Kongsomgan A, Khupulsup K. NGSP and IFCCderived NGSP HbA1c can be used interchangeably. Diabetes Res Clin Pract 2009;8:e22-. 22. National Glycohemoglobin Standardization Program. Summary of NGSP criteria. http://www.ngsp.org/critsumm.asp (Accessed May 28, 2012). 22 www.labmedonline.org