번역 Lab Med Online Vol. 1, No. 3: , July 2011 DOI /lmo 임상화학 이상지혈증환자군의심혈관질환위험등급의분류에서 LDL 콜레스테롤측정치혹은계산치보다 Non-HDL 콜레스테롤이더정확하다 *

번역 Lab Med Online Vol. 1, No. 3: 121-131, July 2011 임상화학 이상지혈증환자군의심혈관질환위험등급의분류에서 LDL 콜레스테롤측정치혹은계산치보다 Non-HDL 콜레스테롤이더정확하다 * Non HDL Cholesterol Shows Improved Accuracy for Cardiovascular Risk Score Classification Compared to Direct or Calculated LDL Cholesterol in a Dyslipidemic Population Hendrick E. van Deventer 1, W. Greg Miller 2, Gary L. Myers 3, Ikunosuke Sakurabayashi 4, Lorin M. Bachmann 2, Samuel P. Caudill 3, Andrzej Dziekonski 2, Selvin Edwards 3, Mary M. Kimberly 3, William J. Korzun 2, Elizabeth T. Leary 5, Katsuyuki Nakajima 6, Masakazu Nakamura 7, Robert D. Shamburek 1, George W. Vetrovec 2, G. Russell Warnick 8 and Alan T. Remaley 1 * National Institutes of Health 1, Bethesda, MD; Virginia Commonwealth University 2, Richmond, VA; Centers for Disease Control Prevention 3, Atlanta, GA; Jichi Medical University 4, Tochigi-ken, Japan; Pacific Biomarkers and Pacific Biometrics Research Foundation 5, Seattle, WA; Otsuka Pharmaceutical 6, Tokyo, Japan; Osaka Medical Center for Health Science and Promotion 7, Osaka, Japan; Health Diagnostics Laboratory 8, Richmond, VA Background: Our objective was to evaluate the accuracy of cardiovascular disease (CVD) risk score classification by direct LDL cholesterol (dldl-c), calculated LDL cholesterol (cldl-c), and non HDL cholesterol (non HDL-C) compared to classification by reference measurement procedures (RMPs) performed at the CDC. Methods: Weexamined 175 individuals, including 138 with CVD or conditions that may affect LDL-C measurement. dldl-c measurements were performed using Denka, Kyowa, Sekisui, Serotec, Sysmex, UMA, and Wako reagents. cldl-c was calculated by the Friedewald equation, using each manufacturer s direct HDL-C assay measurements, and total cholesterol and triglyceride measurements by Roche and Siemens (Advia) assays, respectively. Results: For participants with triglycerides <2.26 mmol/l (<200 mg/dl), the overall misclassification rate for the CVD risk score ranged from 5% to 17% for cldl-c methods and 8% to 26% for dldl-c methods when compared to the RMP. Only Wako dldl-c had fewer misclassifications than its corresponding cldl-c method (8% vs 17%; P <0.05). Non HDL-C assays misclassified fewer patients than dldl-c for 4 of 8 methods (P <0.05). For participants with triglycerides 2.26 mmol/l ( 200 mg/dl) and <4.52 mmol/l (<400 mg/dl), dldl-c methods, in general, performed better than cldl-c methods, and non HDL-C methods showed better correspondence to the RMP for CVD risk score than either dldl-c or cldl-c methods. Conclusions: Except for hypertriglyceridemic individuals, 7 of 8 dldl-c methods failed to show improved CVD risk score classification over the corresponding cldl-c methods. Non HDL-C showed overall the best concordance with the RMP for CVD risk score classification of both normal and hypertriglyceridemic individuals. 번역 : 조선영경희대학교의과대학진단검사의학과 E-mail: untoyou@hanmail.net Received: May 4, 2011 Revision received: May 4, 2011 Accepted: May 4, 2011 This article is available from http://www.labmedonline.org 2011, 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. * 본원고는양잡지의발행인사이의협약에의하여 Clinical Chemistry 에실린영문논문을번역하여게재하는것으로, 본논문을인용하고자할때는다음과같이원논문을인용하여야함. 원논문의저자사사표기및기타원고의내용과관련이없는부분은번역과정에서생략하였음. 참고문헌표기방식은원문방식을그대로사용하였음. 원문인용 : van Deventer HE, Miller WG, Myers GL, Sakurabayashi I, Bachmann LM, Caudill SP, et al. Non-HDL cholesterol shows improved accuracy for car-diovascular risk score classification compared to direct or calculated LDL-cholesterol in a dyslipidemic population. Clin Chem. 2011 Mar;57(3):490-501. eissn 2093-6338 www.labmedonline.org 121

서론 심혈관질환의주요위험인자인저밀도지단백콜레스테롤 (LDL- C) 은지질강하요법의주된목표물질이며다양한심혈관질환의환자의분류에사용된다 [1]. 지단백은크기와지질, 단백질의구성에있어매우다양하다는것이저밀도지단백콜레스테롤에특이적인검사를개발하는것을어렵게만드는원인이다 [2]. 저밀도지단백콜레스테롤 (rldl-c) 과고밀도지단백콜레스테롤 (rhdl-c) 의측정을위한기준측정절차 (reference measurement procedures, RMP) 의검사원리는초원심분리법으로초저밀도지단백 (VLDL) 과암죽미립 (chylomicron) 을분리하고 heparin-manganese 침전을통해 LDL을분리하는것이다 [3]. rldl-c 를일상적으로사용하는것은비실용적이나이는몇몇큰규모의임상연구에의해심혈관질환의생체표지자로밝혀졌으며 [4, 5], 다른검사방법들의비교대상이되는기준법이되고있다 [6]. 최근까지 LDL-C는직접법으로측정하는대신총콜레스테롤, HDL-C, 그리고중성지방을이용한 Friedewald 공식을통해계산하였다 [7]. 그러나이러한방법은중성지방의농도가증가할수록정확도가떨어지고, 제3형고지단백혈증에서는부적합하며금식후의검체가필요하다고알려져있다 [7]. 또한계산에사용되는세가지항목을각각측정하면서발생하는치우침 (bias) 과부정확성은 cldl-c의정확도에나쁜영향을미치고있다 [8]. 이러한제한점에대처하기위해서다양한 dldl-c 측정시약들이개발이되어현재널리사용되고있다 [2]. dldl-c 방법의장점은중성지방의측정에의존하지않으므로인해공복여부에영향을영향을덜받는다는것이다. 또다른장점은다양한형태로검사의완전자동화가가능하기때문에비교적좋은정밀도를나타낸다는것이다 [9]. 그럼에도불구하고 dldl-c 측정에관한이전보고에의하면실제 LDL-C에대해완전히특이적이지못하고또한 cldl-c에비해유의한실용적장점을갖지도못한다 [2, 8, 10, 11]. 그러나이초기의연구들은거의한가지의직접법만을이용하였고, 이상지질혈증환자를대상으로는검사하지않았거나 rldl-c 검사결과와비교하지않았다는제한점을갖는다 [2, 8, 10]. 최근본연구자들은현재이용되는모든 dldl-c 방법과 rldl-c 를비교한연구를마쳤으며이를통해대부분의 dldl-c 방법이 National Cholesterol Education Program (NCEP) 의이상지혈증성검체에대한 LDL-C의측정에있어서대개 β-정량화초원심분리기준측정절차 (RMP) 법이보이는총오차의허용목표에이르지못한다는것을발견하였다 [9]. 본연구에서는같은모집단안에서다양한 dldl-c 측정값과각각의제조사에따른다양한 dhdl-c법을계산에이용한 cldl-c 값으로얻어진심혈관질환위험등급분류결과와 rldl-c 방법을통해얻어진심혈관질환위험등급분류결 과사이의일치도를비교분석하였다. 또한 LDL, HDL, 그리고 non HDL-C의주요단백구성성분인아포지단백 (apo)-b 와 apoa-i을심혈관질환위험등급분류를위해측정하였다. 대상및방법 1. 환자검체 Virginia Common wealth University Medical Center와 NIH에서 institutional review boards (IRB) 의승인을받아참여자를모집하였다. 37명의건강대조군과지질또는심혈관질환클리닉에서모집된대부분의참여자를포함한모집단 (N=175) 에대한설명은이전연구에기술된바와같다 [9]. 전체참여자가운데 104명은 12시간이상금식하였으며, 24명은 10-12 시간, 11명은 8-10시간, 36명은 8시간미만동안각각금식하였다. 혈청은 4 C에서보관되었으며모든검사는검체채취로부터 48시간내에완료되었다. 2. 지질과지단백분석이전연구에서측정된 rldl-c, rhdl-c, dldl-c, dhdl-c, TG, 그리고 TC 결과가사용되었다 [9]. LDL-C, HDL-C 측정을위한초원심분리 RMP는 CDC에서시행되었다. LDL-C와 HDL-C의직접측정법 (Denka Seiken, Kyowa Medex, Sekisui Medical [ 이전의 Daiichi], Serotec, Sysmex International Reagents, UMA, Wako Pure Chemical industries, 그리고 Roche Diagnostics [Kyowa Medex의시약과 Roche Diagnostics 의보정물질및정도관리물질을공급하고있는 ]) 은 Hitachi 917 분석기 (Roche Diagnostics) 로각각의제조사에서제시한지표에따라측정하였다. 총콜레스테롤은 Roche Diagnostics의시약으로 Siemens Advia 1650 분석기로측정하였다. 총중성지방은글리세롤공시료검사없이 Siemens Advia 시약으로 Simens Advia 1650 분석기를사용하여측정하였다. 총콜레스테롤와중성지방측정법의성능을검증코자 CDC 지질표준화사업 (lipid standardization program) 에참여하였으며 [12], CDC-RMPs 와의비교에서나타난평균치우침 (mean bias) 은총콜레스테롤에서는 0.2% (-0.3-0.8%) 였고중성지방에서는 -0.1% (-3.0-2.5%) 였다. LDL-C는위에서기술한바와같이각각의제조사의 dhdl-c와, 총콜레스테롤과중성지방을사용한 Friedewald 공식 (cldl-c [mmol/l] =TC [mmol/l]-hdl-c [mmol/l]-tg [mmol/l]/2.22) 을통해계산되었다 [7]. Non-HDL-C는다음의공식 (non-hdl-c =TC- HDL-C) 으로계산되었으며각각의제조사의지침을따라측정된 dhdl-c를사용하거나위에서언급된방법으로측정된 rhdl-c 과총콜레스테롤을이용하였다. VLDL-C의참고치 (rvldl-c) 는 TC와 RMP로측정된 LDL-C와 HDL-C를측정하여다음의공식으로계산하였는데, ([rvldl-c=tc -rldl-c- rhdl-c] For dldl-c 122 www.labmedonline.org

values <0.08 mmol/l [3 mg/dl]) 단, dldl-c 값이 <0.08 mmol/l (3 mg/dl) 이거나 cldl-c가 <0인경우에는 0.05 mmol/l (2 mg/ dl) 로값을지정하였다. apoa-i와 apob는 -70 C 에서 6-12개월동안보관된동결검체로 Dimension Vista System (Siemens Healthcare Diagnostics) 에서비탁법으로측정하였으며분석당한번씩만측정하였다. 측정결과의소급성을검증하기위해 apob IFCC/WHO 표준 (SP3-08) 과 apoa-i IFCC/WHO 표준 (SP1-01) 을네번반복하여측정하였고지정된값에가까운결과를얻었다 (SP3-08 apob: 118 mg/dl vs mean [SD] 117 [2.2] mg/dl; SP1-01 apoa-1: 150 mg/dl vs 155 [3.7] mg/dl). 3. 통계분석통계분석에는 JMP Statistical Software (SAS Institute) 와 Microsoft Excel의 Analyze-it (Analyze-it Software) 을사용하였다. dldl -C와 cldl-c의수행능을 rldl-c와비교하기위해결정계수 (coefficients of determination) 와가중 Deming 회기분석 (weight-ed Deming regression Analysis) 을이용하여평가하였다. LDL-C 방법의성능은중성지방농도가 <2.26 mmol/l (200 mg/dl) 인군과 2.26 에서 4.52 mmol/l (200 and 400 mg/dl) 사이의군으로나누어평가하였고질환을갖고있거나갖고있지않은참여자를모두포함하였다. 참가자들은 NCEP 기준 [1] 에의해각각의위험군으로분류하였으며이에대한자세한설명은이본문의온라인버전에첨부된추가자료 (online Supplemental) 에기술되어있다 (http:// www.clinchem.org/content/vol57/issue3). dldl-c 또는 cldl-c 에의한오분류의비율이 RMP에서와유의한차이를나타내는지에대한여부를판단하기위해 McNemar법이사용되었다. 이 McNemar 분석에사용된명목형자료는 dldl-c, cldl-c, 그리고 non-hdl-c를각각의 RMP와비교하였을때의오분류비율이었다. 각각의방법에의한오분류율은전에기술한바와같이해당 RMP와비교하였다 [13]. 예를들어, 본연구자들은어떠한 dldl-c 검사법도그에상응하는 cldl-c보다더많이또는더적게환자를오분류하지않는다는귀무가설을설정하였다. 가설의양쪽부분이모두받아들여지지않을때해당검사방법의오분류비율이동등하다는것이확인된다. 결과 1. 중성지방이 2.26 mmol/l (200 mg/dl) 미만인검체에서직접법또는간접법으로측정된 LDL-C의비교 dldl-c 방법과의비교에서나타난 rldl-c 결정계수 (R 2 ) 는 0.85-0.99였고 cldl-c 방법과의비교에서의 rldl-c 결정계수는 0.96-0.98 였다 (Table 1). 모든방법은상대적으로낮은비례오차와고정오차를보였다. 각측정방법으로얻은 dldl-c와 cldl-c 결과는 NCEP 위험도분류에따라심혈관질환위험도점수를분류하는데사용되었고 rldl-c를사용하여위험도를분류한결과와비교하였다. cldl-c법을통해심혈관질환위험도점수가오분류될확률은대략 5-17% 로 dldl-c 방법보다낮았으며각각의해당방법과비교하였을때 8-26% 의확률을나타낸 8가지방법중 5가지방법에서더낮게나타났다. Roche와 Serotec의 dldl-c 방법이상응하는 cldl-c 방법보다통계적으로더많은오분류를나타내었다 (Roche dldl-c 20% vs cldl-c 6%; Serotec dldl-c 27% vs cldl-c 7%). Wako cldl-c법만이상응하는 dldl-c 방법보다유의하게높은오분류를나타내었다 (17% vs 8%) (P <0.05) ( 원문을그대로번역한것이나, 유의하게낮은오분류 로생각됨- 역자주 ). rldl-c 방법과의비교시 dldl-c 방법으로인해더낮은위험도범주로분류된개체의비율은 3% 에서 26% 사이였던반면, 이에비해더높은위험도범주로분류된비율은 1-8% 뿐이었다 (Fig. 1). Denka와 Wako의 dldl-c 방법을제외하면, dldl-c 방법은더많은환자를높은위험도범주로보다는낮은위험도범주로잘못분류하였다. UMA dldl-c 방법으로시행한단 2회의검사에서만이두단계더높은위험도범주로잘못분류한것으로나타났고오분류의방향에있어특정패턴은관찰되지않았다 (Fig. 1). 3가지의 cldl-c 방법은양성치우침를나타냈으며 4가지는음성치우침을보였다. 2. 고중성지방검체에서직접법과간접법으로측정된 LDL-C 법의비교이분석 (Table 1) 은중성지방농도가 2.26 mmol/l (200 mg/ dl) 이고 4.52 mmol/l (400 mg/dl) 인 20명에제한되었고, 이는고중성지방혈증검체에대한 Friedewald equation 의적용자체의한계때문이다. 전반적으로총오류와심혈관질환의위험도분류에있어서 rldl-c와 dldl-c의일치율에대한평가를하였을때 dldl-c 방법은상응하는 cldl-c 방법보다더좋은성능을보였다. dldl-c 방법과비교하였을때 cldl-c 방법또한개체들을더낮은위험군으로분류하는치우침을나타내었다 (Table 1). 3. cldl-c 방법의오류에기여하는원인들에대한분석본연구자들은 Table 2에서 dhdl-c 방법으로 LDL-C 계산을하는과정에서발생한오류의기여정도를나타내었다. 중성지방농도가 <2.26 mmol/l (200 mg/dl) 인환자들에있어서 dhdl-c에대한잔차 (residual SDs, S y x) 는 UMA assay (0.22 mmol/l, 8.5 mg/ dl) 를제외하고모두상대적으로낮았다 (range 0.06-0.08 mmol/l [2.3-3.1 mg/dl]). 중성지방농도가 <2.26 mmol/l (200 mg/dl) 인 www.labmedonline.org 123

Table 1. dldl-c and cldl-c vs rldl-c Denka Kyowa Roche Sekisui dldl-c vs rldl-c [TGs 2.26 mmol/l (200 mg/dl)] (n=145) R 2 0.97 0.98 0.98 0.99 Sy x mmol/l (mg/dl) 0.08 (3.09) 0.08 (3.09) 0.09 (3.48) 0.06 (2.32) Slope (95% CI) 0.99 (0.89 to 1.10) 1.00 (0.88 to 1.12) 0.93 (0.77 to.09) 0.98 (0.92 to 1.05) Intercept (95% CI), mmol/l, mg/dl -0.02 (-0.25 to 0.22), -0.77 (-9.67 to 8.51) -0.06 (-0.33 to 0.22), -2.32 (-12.76 to 8.51) -0.02 (-0.38 to 0.35), -0.77 (-14.69 to 13.53) -0.02 (-0.16 to 0.13), -0.77 (-6.19 to 5.03) % Observed agreement (95% CI),κ 87% (80% to 92%), 0.83 90% (84% to 95%), 0.87 80% (73% to 86%), 0.74 91% (85% to 95%), 0.88 % In lower/higher risk category 6%/8% 8%/2% 19%/1% 7%/2% % Exceeding total error goal 13% 8% 19% 6% cldl-c a vs rldl-c [TGs 2.26 mmol/l (200 mg/dl)] (n=145) R 2 0.98 0.98 0.98 0.98 Sy x mmol/l (mg/dl) 0.07 (2.71) 0.08 (3.09) 0.07 (2.71) 0.08 (3.09) Slope (95% CI) 0.97 (0.86 to 1.08) 0.95 (0.78 to 1.13) 1.00 (0.89 to 1.12) 0.99 (0.86 to 1.13) Intercept (95% CI), mmol/l, mg/dl 0.02 (-0.26 to 0.23), -0.02 (-0.42 to 0.39), -0.06 (-0.33 to 0.20), -0.02 (-0.34 to 0.29), -0.77 (-10.05 to 8.89) -0.77 (-16.24 to 15.08) -2.32 (-12.76 to 7.73) -0.77 (-13.15 to 11.21) % Observed agreement (95% CI),κ 91% (85% to 95%), 0.88 88% (82% to 93%), 0.85 95% (89% to 98%), 0.93 92% (87% to 96%), 0.90 % In lower/higher risk category 7%/2% 10%/1% 3%/3% 3%/5% % Exceeding total error goal 12% 14% 10% 9% dldl-c vs rldl-c [TGs 2.26 mmol/l (200 mg/dl) and 4.52 mmol/l (400 mg/dl)] (n=20) R 2 0.97 0.83 0.82 0.99 Sy x mmol/l (mg/dl) 0.07 (2.71) 0.13 (5.03) 0.13 (5.03) 0.04 (1.55) Slope (95% CI) 1.07 (0.98 to 1.15) 1.10 (0.92 to 1.28) 1.06 (0.88 to 1.24) 1.06 (1.00 to 1.11) Intercept (95% CI), mmol/l, mg/dl -0.12 (-0.31 to 0.07), -4.64 (-11.99 to 2.71) -0.01 (-0.34 to 0.32), -0.39 (-13.15 to 12.37) -0.04 (-0.37 to 0.29), -1.55 (-14.31 to 11.21) -0.09 (-0.24 to 0.06), -3.48 (-9.28 to 2.32) % Observed agreement (95% CI),κ 75% (51% to 91%), 0.69 60% (36% to 81%), 0.52 65% (41% to 85%), 0.57 90% (68% to 99%), 0.87 % In lower/higher risk category 10%/15% 5%/35% 15%/20% 0%/10% % Exceeding total error goal 5% 30% 15% 0% cldl-c a vs rldl-c [TGs 2.26 mmol/l (200 mg/dl) and 4.52 (400 mg/dl)] (n=20) R 2 0.84 0.85 0.85 0.83 Sy x mmol/l (mg/dl) 0.16 (6.19) 0.15 (5.80) 0.15 (5.80) 0.16 (6.19) Slope (95% CI) 1.15 (0.94 to 1.36) 1.15 (0.96 to 1.33) 1.16 (0.97 to 1.35) 1.15 (0.95 to 1.35) Intercept (95% CI), mmol/l, mg/dl -0.53 (-1.00 to -0.06), -20.49 (-38.67 to -2.32) -0.46 (-0.86 to -0.07), -53.75 (-33.26 to -2.71) -0.44 (-0.85 to -0.03), -17.01 (-32.87 to -12.76) -0.45 (-0.87 to -0.03), -17.40 (-33.64 to -1.16) % Observed agreement (95% CI),κ 50% (27% to 73%), 0.38 55% (32% to 77%), 0.43 65% (41% to 85%), 0.57 45% (23% to 69%), 0.31 % In lower/higher risk category 35%/15% 35%/10% 20%/15% 35%/20% % Exceeding total error goal 40% 40% 40% 45% (Continued to the next page) 124 www.labmedonline.org

Table 1. (Continued from the previous page) dldl-c and cldl-c vs rldl-c Serotec Sysmex UMA Wako 0.97 0.97 0.85 0.99 0.08 (3.09) 0.12 (4.64) 0.18 (6.96) 0.05 (1.93) 0.91 (0.81 to 1.01) 0.91 (0.63 to 1.20) 0.99 (0.90 to 1.07) 0.99 (0.98 to 1.01) -0.01 (-0.25 to 0.22), -0.39 (-9.67 to 8.51) 0.11 (-0.65 to 0.65), 0.00 (-25.14 to 25.14) -0.04 (-0.23 to 0.15), -1.55 (-8.89 to 5.80) 0.05 (0.02 to 0.09), 1.93 (0.77 to 4.38) 74% (66% to 81%), 0.66 82% (75% to 88%), 0.76 86% (79% to 91%), 0.81 92% (86% to 96%), 0.89 265%/1% 7%/1% 9%/6% 3%/5% 35% 26% 15% 4% 0.98 0.98 0.96 0.97 0.07 (2.71) 0.08 (2.97) 0.12 (4.64) 0.05 (1.93) 0.99 (0.90 to 1.08) 1.00 (0.89 to 1.10) 0.93 (0.71 to 1.16) 0.93 (0.52 to 1.33) -0.02 (-0.22 to 0.19), 0.01 (-0.23 to 0.25), 0.04 (-0.48 to 0.55), -0.02 (-0.93 to 0.89), -0.77 (-8.51 to 7.35) 0.49, (-8.80 to 9.74) 1.55 (-18.56 to 21.27) -0.77 (-35.96 to 34.42) 93% (88% to 97%), 0.91 90% (80% to 93%), 0.87 84% (77% to 90%), 0.79 83% (76% to 89%), 0.78 2%/5% 1%/9% 10%/6% 15%/1% 8% 10% 15% 25% 0.82 0.84 0.74 0.98 0.14 (5.41) 0.13 (5.03) 0.16 (6.19) 0.05 (1.93) 1.04 (0.83 to 1.24) 1.12 (0.93 to 1.31) 1.07 (0.85 to 1.35) 0.97 (0.91 to 1.04) -0.30 (-0.75 to 0.16), -11.60 (-29.00 to 6.19) -0.32 (-0.72 to 0.08), -12.37 (-27.84 to 3.09) 0.14 (-0.29 to 0.56), 5.41 (-11.21 to 21.66) 0.27 (0.12 to 0.43), 10.44 (4.64 to 16.63) 70% (46% to 88%), 0.62 80% (56% to 94%), 0.75 45% (23% to 69%), 0.33 70% (46% to 88%), 0.62 25%/5% 15%/5% 10%/45% 5%/25% 45% 10% 45% 30% 0.85 0.83 0.83 0.82 0.15 (5.80) 0.15 (5.80) 0.16 (6.19) 0.16 (6.19) 1.17 (0.99 to 1.35) 1.15 (0.96 to 1.34) 1.15 (0.96 to 1.35) 1.18 (0.96 to 1.41) -0.47 (-0.85 to -0.09), -18.17 (-32.87 to -3.48) -0.40 (-0.79 to -0.02), -15.47 (-30.55 to -0.77) -0.41 (-0.82 to -0.00), -15.85 (-31.71 to 0.00) -0.66 (-1.17 to -0.15), -25.52 (-45.24 to -5.80) 60% (36% to 81%), 0.50 55% (32% to 77%), 0.45 50% (27% to 73%), 0.38 50% (27% to 73%), 0.38 20%/20% 25%/20% 25%/25% 35%/15% 40% 35% 40% 50% a cldl-c was calculated using direct HDL-C from each indicated manufacturer. www.labmedonline.org 125

환자의경우 dhdl-c법의 6-20% 의결과가총오차허용범주를넘었다. rhdl-c를이용한심혈관질환의위험도분류와비교했을때, dhdl-c 측정법 (Table 2) 에서 dldl-c 측정법 (Table 1) 보다적은오분류가발생하였다. Sekisui법을제외하고모든 dhdl-c 방법에서 TG 농도 2.26 mmol/l (200 mg/dl) 인환자군에서는총오차허용범주를넘는결과의실제적인증가가나타났다. Friedewald 공식에서사용되는 TG (mmol/l)/2.22 이라는용어는 VLDL-C의추정을가능하게하는반면, cldl-c의또다른오류의원인이된다. 오류의일부는내인성글리세롤제외여부가포함되는중성지방측정의부정확성과치우침때문이다. 또한중성지방은대략 20% 에이르는상대적으로높은생물학적변이를나타내므로이또한 LCL-C의계산오류에기여하게된다 [14]. 본연구집단에서 TG (mmol/l)/2.22 와 VLDL-C (N=144, 한개의 outlier는제외 ) 은상대적으로약한상관관계를나타내고 (R 2 = 0.65), 상대적으로높은잔차 (0.12 mmol/l [4.9 mg/dl]) 를보였는데, 이는 TG<2.26 mmol/l (<200 mg/dl) 인개체들에게서조차나타났고 dhdl-c 방법에의한오류와비교하면약 2배에가까운수치였다. 4. 심혈관질환위험도분류를위한 non-hdl 콜레스테롤 (non-hdl-c) Non-HDL-C은모든 apob 함유입자와관련이있는콜레스테롤의측정치로, 이를심혈관질환의위험도분류의대안으로삼아분석하였다 (Table 3). Non-HDL-C는 VLDL-C의측정과관련된오류에영향을받지않으며다양한종류의 apob 함유지단백에대한 dldl-c 방법에서발생하는지단백의특이도에관련된문제에영향을받지않는다. TG 농도 <2.26 mmol/l (200 mg/dl) 인환자들에서 dhdl-c 방법을사용하여계산된 non-hdl-c는 rhdl-c에의해계산된 non-hdl-c와강한상관관계를보였다 (R 2 >0.97). Non-HDL-C 방법의표준법으로분류한경우와의비교에서 non- HDL-C법으로분류된환자가더낮은위험군으로분류된경우는 0-11% 였던반면, 더높은위험군으로잘못분류된경우는 1-8% 였다. Wako dldl-c를제외하고 non-hdl-c 방법은전반적으로 dldl-c 또는 cldl-c 방법보다더적은오분류를하는것으로나타났다 (Fig. 1). TG 농도가 2.26 mmol/l (200 mg/dl) 그리고 <4.52 mmol/l (400 mg/dl) 인환자군에서 non-hdl 방법은 dldl-c 또는 cldl-c 방법보다 RMP와일반적으로더좋은일치도를보였다. 더낮은위험군으로분류된경우는 0-7% 였으며 8-18% 는더높은위험군으로분류되었는데이는 dldl-c과 cldl-c 방법에서보다좋은결과였다. 5. 심혈관질환위험도분류를위한 apob와 apoa-i apob는모든 dldl-c 방법과낮은일치도를보였고결정계수는 0.47에서 0.61로나타났다. apob와 rldl-c 사이의결정계수역시상대적으로낮았다 (R 2 = 0.56). 그러나 apob와 non-hdl-c 사이의결정계수는 0.83에서 0.84로더높게나타났다. Non-HDL-C 기준법을 apob와비교하였을때의결정계수는 0.86이었다. apoa-i와 rhdl-c의연관성이상당히강하게나타났다 (R 2 = 0.81). 그러나이에비해 apoa-i과다양한 dhdl-c 방법들사이의연관성은결정계수가 0.66에서 0.83 사이로다양하게나타났다. 고찰이연구의가장중요한발견은 dldl-c 방법이이상지혈증환자들을 NCEP 위험도분류로나누는데있어 rldl-c와비교하였을때 cldl-c보다더나은점을보여주지못하였다는것이다. 오히려심혈관질환의위험도분류에있어서중성지방농도 <2.26 mmol/ L (200 mg/dl) 인환자군에서 Roche사와 Serotec사의 dhdl-c 방법에의한 cldl-c 값은각각에상응하는 dldl-c 방법보다 rldl- C에더근접하였다. 그러나중성지방농도 2.26 mmol/l (200 mg/dl) 인환자군에서는 dldl-c 방법이 cldl-c에의한심혈관위험도분류보다더나은결과 (Table 1) 를보였는데, 이는고중성지방혈증검체 (Table 2) 에서 dhdl-c의낮은수행능과 VLDL-C 측정의부정확성때문이다. 이러한결과는실용적이고비용적인측면을고려하였을때중성지방농도 <2.26 mmol/l (200 mg/dl) 인환자군에서는 dldl-c의추가적인측정없이 cldl-c를위험도분류에사용하는것이적절하다는것을보여준다. dldl-c 방법은중성지방농도 2.26 mmol/l (200 mg/dl) 인환자군에서가장적합하였고이환자군에서정확하게환자를분류하는장점을보였다. dldl-c와 clcl-c 방법으로심혈관질환의위험도를평가할경우고려해야할다른요소는개체내생물학적변동과검체채취전금식이요구된다는점이다. 총콜레스테롤, 중성지방그리고 HDL-C의세가지변수들의생물학적변동은 cldl-c에영향을미칠지라도 cldl-c의개체내다양성은 dldl-c와비슷한정도였다 (cldl-c 은 7.3% [0.6%], dldl-c은 6.8% [0.5%]) [8]. 정확하게 cldl- C를측정하려면검체를채취하기전환자의금식이요구된다 [15, 16]. 그러므로 dldl-c의잠재적이점은비금식검체의사용을가능하게한다는것이다. 그러나 dldl-c 방법 (Hitachi 917 analyzer, Roche Diagnostics) 에대한최근의한연구에의하면금식하지않고측정한 dldl-c이심혈관질환의위험도와좋은연관성을보여주지못했고, 이것은 dldl-c 방법에있어서만큼은금식하지않은환자군에서의임상적인유용성에대해의문을갖게한다 [17, 18]. dldl-c 방법 (Sigma Diagnostics) 을평가한또다른연구도비금식 126 www.labmedonline.org

Table 2. dhdl-c vs rhdl-c Denka Kyowa Roche Sekisui Serotec Sysmex UMA Wako dhdl-c vs rhdl-c [TGs 2.26 mmol/l (200 mg/dl)] (n=146) R 2 0.97 0.99 0.98 0.98 0.97 0.97 0.85 0.98 Sy x mmol/l (mg/dl) 0.08 (3.09) 0.06 (2.32) 0.06 (2.32) 0.07 (2.71) 0.08 (3.09) 0.08 (3.09) 0.22 (8.51) 0.07 (2.71) Slope (95% CI) 1.07 (1.02 to 1.12) 1.12 (1.08 to 1.15) 1.06 (1.02 to 1.09) 1.01 (0.97 to 1.05) 1.09 (0.99 to 1.19) 1.01 (0.94 to 1.07) 1.29 (1.21 to 1.37) 0.98 (0.93 to 1.04) Intercept (95% CI), mmol/l, mg/dl -0.08 (-0.13 to -0.02), -3.09 (-5.03 to -0.77) -0.11 (-0.15 to -0.07), -4.25 (-5.80 to -2.71) -0.10 (-0.14 to -0.61), -3.87 (-5.41 to -2.32) -0.06 (-0.11 to -0.02), -2.32 (-4.25 to -0.77) -0.16 (-0.28 to -0.03), -6.19 (-10.83 to -1.16) -0.09 (-0.17 to -0.01), -3.48 (-6.57 to -0.39) -0.33 (-0.41 to -0.26), -12.76 (-15.85 to -10.05) 0.10 (0.03 to 0.17), 3.87 (1.16 to 6.57) % Observed agreement (95% CI),κ 93% (88% to 97%), 0.88 91% (85% to 95%), 0.86 93% (88% to 97%), 0.89 93% (88% to 97%), 0.89 91% (85% to 95%), 0.86 88% (81% to 93%), 0.81 86% (80% to 91%), 0.79 87% (80% to 92%), 0.80 % In lower/higher risk category 5%/3% 1%/8% 5%/1% 7%/0% 8%/1% 12%/0% 5%/8% 1%/12% % Exceeding total error goal 6% 8% 6% 8% 12% 16% 17% 20% dhdl-c vs rhdl-c [TGs 2.26 mmol/l (200 mg/dl)] (n=28) R 2 0.93 0.97 0.96 0.98 0.78 0.9 0.62 0.8 Sy x mmol/l (mg/dl) 0.10 (3.87) 0.11 (4.25) 0.11 (4.25) 0.07 (2.71) 0.26 (10.05) 0.38 (14.69) 0.21 (8.12) 0.18 (6.96) Slope (95% CI) 1.10 (0.91 to 1.29) 0.93 (0.58 to 1.27) 0.85 (0.51 to 1.21) 1.07 (0.90 to 1.23) 0.58 (0.37 to 0.79) 1.07 (0.02 to 2.11) 0.91 (0.82 to 1.00) 0.62 (0.00 to 1.24) Intercept (95% CI), mmol/l, mg/dl -0.02 (-0.18 to 0.13), -0.77 (-6.96 to 5.03) 0.08 (-0.22 to 0.38), 3.09 (-8.51 to 14.69) 0.10 (-0.20 to 0.41), 3.87 (-7.73 to 15.85) -0.07 (-0.20 to 0.07), -2.71 (-7.73 to 2.71) 0.38 (0.19 to 0.57), 14.69 (-7.35 to 22.04) -0.12 (-1.05 to 0.80), -4.64 (-40.60 to 30.94) 0.06 (0.02 to 0.09), 2.32 (-0.77 to 3.48) 0.45 (-0.12 to 1.03), 17.40 (-4.64 to 39.83) % Observed agreement (95% CI),κ 89% (72% to 98%), 0.76 89% (72% to 98%), 0.73 86% (67% to 96%), 0.63 86% (67% to 96%), 0.63 82% (63% to 94%), 0.55 79% (59% to 92%), 0.40 79% (59% to 92%), 0.56 75% (55% to 89%), 0.52 % In lower/higher risk category 4%/7% 11%/0% 14%/0% 14%/0% 14%/4% 21%/0% 14%/7% 0%/25% % Exceeding total error goal 25% 11% 14% 7% 25% 25% 29% 43% www.labmedonline.org 127

Table 3. Comparison of results and classification based on direct non HDL-C vs RMP non HDL-C Denka Kyowa Roche Sekisui Serotec Sysmex UMA Wako Non HDL-C vs RMP non HDL-C [TGs 2.26 mmol/l (200 mg/dl)] (n=146) R 2 0.997 0.997 0.997 0.997 0.996 0.995 0.973 0.997 Sy x mmol/l (mg/dl) 0.04 (1.55) 0.03 (1.16) 0.03 (1.16) 0.03 (1.16) 0.05 (1.93) 0.04 (1.55) 0.09 (3.48) 0.04 (1.55) Slope (95% CI) 1.00 (0.90 to 1.10) 1.00 (0.95 to 1.04) 1.01 (0.96 to 1.07) 1.00 (0.96 to 1.05) 1.04 (0.90 to 1.17) 1.00 (0.93 to 1.08) 1.00 (0.93 to 1.08) 0.99 (0.90 to 1.07) -0.05 (-0.28 to 0.18), -1.93 (-10.83 to 6.96) 0.09 (-0.11 to 0.28), 3.48 (-4.25 to 10.83) 0.09 (-0.11 to 0.28), 3.48 (-4.25 to 10.83) -0.05 (-0.42 to 0.32), -1.93 (-16.24 to 12.37) 0.05 (-0.06 to 0.16), 1.93 (-2.32 to 6.19) 0.00 (-0.15 to 0.16), 0.00 (-5.80 to 6.19) -0.02 (-0.13 to 0.10), -0.77 (-5.03 to 6.19) -0.01 (-0.28 to 0.27), -0.39 (-10.83 to 10.44) Intercept (95% CI), mmol/l, mg/dl % Observed agreement (95% 97% (92% to 99%), 95% (90% to 98%), 95% (90% to 98%), 95% (90% to 98%), 93% (88% to 97%), 93% (87% to 96%), 90% (84% to 95%), 88% (81% to 93%), CI), 0.95 0.93 0.93 0.94 0.91 0.90 0.87 0.83 % In lower/higher risk category 2%/1% 4%/1% 0%/5% 0%/5% 1%/6% 0%/8% 5%/4% 12%/1% % Exceeding total error goal 2% 1% 1% 2% 2% 4% 8% 3% Non HDL-C vs RMP non HDL-C [TGs 2.26 mmol/l (200 mg/dl)] (n=28) R 2 0.998 0.998 0.996 0.999 0.965 0.996 0.979 0.992 Sy x mmol/l (mg/dl) 0.02 (0.77) 0.01 (0.39) 0.02 (0.77) 0.02 (0.77) 0.04 (1.55) 0.02 (0.77) 0.06 (2.32) 0.03 (1.16) Slope (95% CI) 0.99 (0.97 to 1.01) 1.00 (0.97 to 1.02) 1.00 (0.97 to 1.02) 1.01 (0.99 to 1.02) 0.99 (091 to 1.06) 1.01 (0.98 to 1.04) 1.01 (0.95 to 1.06) 0.99 (0.96 to 1.03) -0.10 (-0.26 to 0.06), -3.87 (-10.05 to 2.32) -0.02 (-0.32 to 0.28), -0.77 (-12.37 to 10.83) 0.03 (-0.07 to 0.14), 1.16 (-2.71 to 5.41) 0.06 (-0.22 to 0.34), 2.32 (-8.51 to 13.15) -0.01 (-0.06 to 0.05), -0.39 (-2.32 to 1.93) 0.04 (-0.06 to 0.14), 1.55 (-2.32 to 5.41) 0.00 (-0.08 to 0.09), 0.00 (-3.09 to 3.48) -0.02 (-0.10 to 0.06), -0.77 (-3.87 to 2.32) Intercept (95% CI), mmol/l, mg/dl % Observed agreement (95% 100% (88% to 100%), 93% (77% to 99%), 89% (72% to 98%), 93% (77% to 97%), 89% (72% to 98%), 82% (63% to 94%), 79% (59% to 92%), 93% (77% to 99%), CI), 1.00 0.91 0.87 0.91 0.87 0.78 0.74 0.91 % In lower/higher risk category 0%/0% 0%/7% 0%/11% 0%/7% 0%/11% 0%/18% 4%/18% 7%/0% % Exceeding total error goal 0% 0% 0% 0% 4% 0% 4% 7% % Miscalassified Lower Higher % Miscalassified Lower Higher % Miscalassified Lower Higher 9 4-1 -6-11 -16-21 -26 9 4-1 -6-11 -16-21 -26 9 4-1 -6-11 -16-21 -26 De Ky Ro Sk Sr Sy Um Wa De Ky Ro Sk Sr Sy Um Wa De Ky Ro Sk Sr Sy Um Wa Fig. 1. Misclassification rate for CVD risk for those participants with TG levels <2.26 mmol/l (200 mg/dl), N=145. Percent of test results that were classified into either a higher (shaded bar) or lower (hatched bar) CVD risk category compared to RMPs are shown for dldl-c (A), cldl-c (B), or non HDL-C (C). De, Denka; Ky, Kyowa; Ro, Roche; Sr, Serotec; Sk, Sekisui, Sy, Sysmex; Um, UMA; Wa, Wako. 환자군에서상대적으로낮은수행도를나타내었다 [19]. 다른연구 들도몇몇환자들에서식후에생리적으로 LDL-C 값이감소하는 현상을밝혀냈다 [15, 20, 21]. 제 3 차 Adult Treatment Panel of the NCEP 는모든 apob 함유지 단백을포함하는 non-hdl-c 를 TG 농도 2.26 mmol/l (200 mg/ dl) 인환자군에서지질강하의이차적목표로사용하기를현재권 장하고있다 [1]. 이연구에서는각각의해당 RMP 와비교하였을때, non-hdl-c 가중성지방과상관없이 dldl-c 와 c-ldl-c 보다더 오분류가낮게나타났다 (Fig. 1). 이러한낮은오분류율은 dldl-c 와 cldl-c 방법이모두저조한수행능을보인중성지방농도 2.26 mmol/l (200 mg/dl) 인환자군에서더욱현저하였다. Non- A B C 128 www.labmedonline.org

HDL-C은 2가지의측정물질을필요로하므로 3가지측정물질을필요로하는 cldl-c보다비용을감소시킨다. Non-HDL-C를일차적선별검사로권고할수있기위해서는해당 RMP에대해향상된상응도를보임이입증되어야할뿐만아니라 non-hdl-c이적어도심혈관질환을예측하는데있어서 LDL-C 과동등하다는것을보여주어야한다. 중성지방이증가한당뇨환자의경우에서는심혈관질환위험도를예측하는데있어 non-hdl- C는 LDL-C보다명백히우월함이여러연구를통해밝혀졌다 [22-24]. 이것은잔류지단백과같은 LDL 이외의 apob 함유지단백들이당뇨환자의죽상경화의병리기전에크게기여하기때문일것이다. 몇몇대형역학연구에서도일반인구집단에서 non-hdl-c이심혈관질환의위험도를예측하는데있어서 LDL-C와 apob보다더우월하거나최소한동등하다는것을보여주었다 [25-28]. Framingham Heart study는 non-hdl-c이중성지방이증가하거나참고범위내에있을때에 LDL-C 보다더우월하다고밝혔다 [29, 30]. 더나아가 non-hdl-c는금식하지않은개체에서도심혈관질환을예측할수있었다 [29, 30]. 30만명을포함하는 68개의연구에대한최근의한메타분석은 non-hdl-c와 LDL-C의심혈관질환에대한위험비가 LDL-C를다양한방법으로직접측정하거나계산하여구한경우와비교할때최소한동등하다고보고하였다 [31]. American Diabetes Association and American College of Cardiology에의한최근의지침은콜레스테롤치료의목표에서 apob가 LDL-C보다우수하다고제시하고있다 [32]. apoa-i 역시몇몇연구에서심혈관질환위험도평가에있어 HDL-C과동등하거나우수하였다 [33, 34]. 이번연구결과에서는 apob와 apoa-i를 rldl-c와 rhdl-c에비교하였을때, 각각 17% 와 13% 를더낮은심혈관질환위험군으로재분류하였고각각 22% 와 5% 를더높게분류하였다. 이연구에서는임상적결과에대한자료가없기때문에위의두가지 apo 방법에의한재분류의임상적정확도에대한판단은할수없었다. 본연구의다른제한점은 apob (SP3-08) 와 apoa-i (SP1-01) 방법이 IFCC/WHO 기준에잘부합했지만, 단한가지씩의 apob와 apoa-i 방법만이사용되었다는점이다. 임상결과 (clinical end points) 를이용한최근의한전향적연구는 apob와 apoa-i (Behring Nephelometer, BNII) 가심혈관질환위험도재분류를 cldl- C와 HDL-C (RA-1000 analyzer, Bayer Diagnostics) 보다향상시키지못한다고밝힌바있다 [35]. 본연구에서몇가지한계점이있다는것을주목하는것이중요하다. rldl-c을측정하기위해사용된 β-정량법은중밀도지단백 (IDL) 과 lipoprotein(a) 의콜레스테롤에도민감할수있다는것이다 [2]. 그러므로본연구에서사용된 dldl-c 방법에서나타난것처럼 LDL에만전적으로특이적인 dldl-c 방법은 β-정량법을사용한 rldl-c와비교하였을때음성치우침를나타내게된다. 그러 나이러한또다른죽상경화성 apob 함유지단백분획 [36, 37] 은 cldl-c와 non-hdl-c 값에영향을주게되며적어도일정부분은이러한표지자를통한심혈관질환의위험도분류의수행능을향상시키는데기여할수있다. 본연구의또다른제한점은다양한방법을통한심혈관질환의위험도의정확성에있어서금식한집단이다른집단과유의한차이점을나타내지않았을지라도모든환자가금식을하지는않았다는것이다 (71명의참여자가 <12시간금식하였음 ). 또한사용된방법이 CDC 지질표준화프로그램에의해검증된정확도를갖는방법이라할지라도총콜레스테롤과중성지방이한가지방법만으로측정되었다는것이다. 이연구의약 80% 의검체가이상지혈증을나타내는환자로부터얻어졌기때문에본연구가다른인구집단에는적용될수없을수도있다. 그러나이환자군은정확한지질과지단백의측정이가장중요한집단이라는점에서중요하다. 마지막으로연구의검체수가상대적으로적었고특히 TG 2.26 mmol/l (200 mg/dl) 그리고 <4.52 mmol/l (400 mg/dl) 인부분집단이특히부족하였다 (N=20). 요약하면고중성지방검체를제외하면 8가지중 7가지의 dldl- C 방법이 cldl-c보다심혈관질환의위험도분류의정확도를향상시키지못하였다. 이이유는적어도부분적으로라도 dhdl-c 방법이 dldl-c 방법보다 RMP와일반적으로더큰일치도를보인다는점이작용했기때문이다. 전반적으로는 dhdl-c 결과를사용하는 non-hdl-c 방법이 TG가높은검체와낮은검체모두에서 dldl- C이나 cldl-c 방법보다 RMP와더좋은일치도를보였으며심혈관질환위험도분류에서도더나은조화도를보였다. 임상결과를포함하는앞으로의연구는 LDL-C와 HDL-C의다양한직접법이갖는임상적의미를파악하고초원심분리 RMP법과비교된이러한직접법에의해측정되거나제외된지단백분획의임상적의미의불확실성을해결하기위해시행되어야할것이다. 요약 배경 : 본연구의목적은직접법으로측정된저밀도지단백콜레스테롤 (direct LDL-C, LDL-C) 과간접법으로계산된저밀도지단백콜레스테롤 (calculated LDL-C, cldl-c), 그리고비고밀도지단백콜레스테롤 (non-hdl-c) 에의한심혈관질환의위험등급분류를 CDC에서시행된참고치측정방법 (reference measurement procedures, RMP) 에따른분류와비교함으로서그정확도를평가하고자하였다. 방법 : 본연구는심혈관질환등 LDL-C의측정에영향을줄수있는조건을가진 138명을포함한 175명을대상으로시행되었다. dldl-c 측정을위해사용된시약은 denka, kyowa, sekisui, serotec, sysmex, UMA, 그리고 wako였다. cldl-c는 Friedewald 공식 www.labmedonline.org 129

을이용하여계산하였으며직접법으로측정된 direct HDL-C (dh- DL-C), 총콜레스테롤 (TC), 중성지방 (TG) 을각각의제조사의지침에따라 Roche와 Simens (Advia) 검사법통해측정하였다. 결과 : TG <2.26 mmol/l (<200 mg/dl) 인참여자들을대상으로 RMP와비교하였을때, 심혈관질환의위험등급의오분류비율은 cldl-c에서 5-17%, dldl-c 방법에서 8-26% 로나타났다. Wako 시약을통해측정된 dldl-c에서만해당 cldl-c 방법보다오분류의비율이낮았다 (8% vs 17%; P <0.05). Non-HDL-C 방법 8가지중 4가지의방법이 dldl-c 방법보다적은오분류를나타내었다 (P <0.05). TG 2.26 mmol/l ( 200 mg/dl) 이고 <4.52 mmol/l (<400 mg/dl) 인참여자들에서는 dldl-c 방법이 cldl- C 방법보다우수했으며심혈관질환위험도에서도 non-hdl-c 방법이 d-ldl-c와 cldl-c 방법보다 RMP 방법에더일치하는결과를나타내었다. 결론 : 고중성지방혈증을나타내는경우을제외하고는 8가지중 7가지의 dldl-c 방법에서해당 cldl-c 방법과비교시더향상된심혈관질환의위험등급의분류를나타내지못하였다. 정상인경우와고중성지방혈증에서모두 non-hdl-c 방법이전반적으로 RMP를통한심혈관질환위험등급분류와가장일치하는결과를나타내었다. 참고문헌 1. Executive Summary of the Third Report of the National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel III). JAMA 2001;285:2486-97. 2. Nauck M, Warnick GR, Rifai N. Methods for measurement of LDL-cholesterol: a critical assessment of direct measurement by homogeneous assays versus calculation. Clin Chem 2002;48:236-54. 3. Nauck M, Wiebe D, Warnick GR. Measurement of high-density-lipoprotein cholesterol. In: Rifai N, Warnick GR, Dominiczak MH, eds. Handbook of lipoprotein testing. 2nd ed. Washington, DC: AACC Press; 2000:227-30. 4. Gordon T, Kannel WB, Castelli WP, Dawber TR. Lipoproteins, cardiovascular disease, and death. The Framingham study. Arch Intern Med 1981;141:1128-31. 5. Castelli WP, Doyle JT, Gordon T, Hames CG, Hjortland MC, Hulley SB, et al. HDL cholesterol and other lipids in coronary heart disease. The cooperative lipoprotein phenotyping study. Circulation 1977;55:767-72. 6. Myers GL, Kimberly MM, Waymack PP, Smith SJ, Cooper GR, Sampson EJ. A reference method laboratory network for cholesterol: a model for standardization and improvement of clinical laboratory measurements. Clin Chem 2000;46:1762-72. 7. Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem 1972;18:499-502. 8. Schectman G, Patsches M, Sasse EA. Variability in cholesterol measurements: comparison of calculated and direct LDL cholesterol determinations. Clin Chem 1996;42:732-7. 9. Miller WG, Myers GL, Sakurabayashi I, Bachman LM, Caudill SP, Dziekonski A, et al. Seven direct methods for measuring HDL and LDL cholesterol compared with ultracentrifugation reference measurement procedures. Clin Chem 2010;56:977-86. 10. Sahu S, Chawla R, Uppal B. Comparison of two methods of estimation of low density lipoprotein cholesterol, the direct versus Friedewald estimation. Indian J Clin Biochem 2005;20:54-61. 11. Miller WG, Waymack PP, Anderson FP, Ethridge SF, Jayne EC. Performance of four homogeneous direct methods for LDL-cholesterol. Clin Chem 2002;48:489-98. 12. Warnick GR, Kimberly MM, Waymack PP, Leary ET, Myers GL. Standardization of measurements for cholesterol, triglycerides, and major lipoproteins. Lab Med 2008;39:481-90. 13. Lachenbruch PA and Lynch CJ. Assessing screening tests: extensions of McNemar s test. Stat Med 1998;17:2207-17. 14. Ricos C, Alvarez V, Cava F, Garcia-Lario J, Hernandez A, Jimenez CM, J, et al. Current databases on biological variation: pros, cons and progress. Scand J Clin Lab Invest 1999;59:491-500. 15. Cohn JS, McNamara JR, Schaefer EJ. Lipoprotein cholesterol concentrations in the plasma of human subjects as measured in the fed and fasted states. Clin Chem 1988;34:2456-9. 16. Rifai N, Merrill JR, Holly RG. Postprandial effect of a high fat meal on plasma lipid, lipoprotein cholesterol and apolipoprotein measurements. Ann Clin Biochem 1990;27:489-93. 17. Mora S, Rifai N, Buring JE, Ridker PM. Fasting compared with nonfasting lipids and apolipoproteins for predicting incident cardiovascular events. Circulation 2008;118:993-1001. 18. Mora S, Rifai N, Buring JE, Ridker PM. Comparison of LDL cholesterol concentrations by Friedewald calculation and direct measurement in relation to cardiovascular events in 27,331 women. Clin Chem 2009; 55:888-94. 19. Yu HH, Ginsburg GS, Harris N, Rifai N. Evaluation and clinical application of a direct low-density lipoprotein cholesterol assay in normolipidemic and hyperlipidemic adults. Am J Cardiol 1997;80:1295-9. 130 www.labmedonline.org

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