一种尿液HIV-1抗体EIA试剂现场使用评价

目的　现场评价 Calypte TM尿液 HIV- 1抗体 EIA试剂。　方法　同时采集 112 0名吸毒者的尿液与血液 ,分别用 Calypte TM尿液试剂盒和 Vironostika R○ HIV Uni- Form Plus O血液试剂盒进行初筛检测 ,两种方法重复检测阳性样本 ,用蛋白印迹法确认 ,对检测结果进行比较。　结果　 Calypte TM尿液试剂盒的敏感性、特异性和功效值分别为10 0 %、99.1%和 99.1%,与确认结果比较 ,阳性符合率为 10 0 %。　结论　 Calypte TM尿液 HIV - 1抗体 EIA试剂盒在HIV- 1流行区 ,可以考虑作为替代血液检测试剂盒。     

人血液和尿液样本HIV-1抗体的ELISA 检测比较

目的 比较人的血液和尿液样本中HIV-1抗体的一致性。方法 在广东省两所劳动教养所收集346名HIV高危的血液和尿液样本，分别用血液和尿液ELISA初筛试剂检测HIV-1抗体。结果 346份血液和尿液样本各18份阳性，其中有17人的血液和尿液平行样本均为HIV—1抗体阳性，血液和尿液样本HIV-1抗体检测的一致性为99．4％。结论 在采集血液样本不便的情况下，可利用尿液ELISA初筛诊断试剂进行HIV感染的筛查和监测。     

垂直流免疫印迹法检测尿液HIV-1抗体的技术研究

目的 利用垂直流技术的快速性与免疫印迹法(WB)检测的精确性,建立垂直流免疫印迹检测技术(VWB),探讨其在检测尿液HIV-1抗体的临床意义.方法 通过SDS-PAGE电泳和电转,将HIV-1抗原包被于硝酸纤维素膜(NC膜)上,然后将膜黏合于自制反应槽的底部,并与真空抽滤系统结合构成垂直流免疫印迹法检测装置.利用该装置对临床样本(12例HIV-1抗体阳性尿液样本,10例HIV-1抗体阴性尿液样本)进行检测,并与传统WB法的检测结果相比较.结果 VWB法检测尿液样本阳性符合率为100%,阴性符合率为100%,主要抗原蛋白带符合率高于WB法检测尿液样本.结论 VWB法检测尿液样本的结果与WB法检测血清样本的结果基本一致,是HIV-1感染确认检测方法的又一补充技术.     

一种快速检测HIV抗体方法的评价

目的：探讨一种快速检测人类免疫缺陷病毒（HIV）抗体方法的敏感性和特异性,为艾滋病自愿咨询检测（VCT）及各种应急检测提供参考依据。方法：选择MSM调查人群血样1010份,平行用抗HIV-1／2快速检测（RT）试剂与抗HIV-1／2酶联免疫（ELISA）试剂进行检测,凡结果阳性者均用免疫印迹法（WB）进行确认。结果：710份血浆标本两种方法均有42份阳性,两者相符;300份全血标本用RT法检测,19份阳性,ELISA法22份阳性,3份不符标本后用血浆重复用RT法检测为阳性。所有阳性标本经WB确认均判为阳性。结论：HIV抗体快速检测试剂的使用需满足质量保证的要求并做好检测前后的咨询。建议使用经权威机构推荐的快速检测试剂;对于采供血机构,应使用ELISA法进行检测。     

尿液HIV-1抗体检测及其临床意义

目的探讨尿液标本中人免疫缺陷病毒(HIV)-1抗体检测的临床意义。方法应用酶联免疫吸附试验(ELISA)对59例经疾病预防控制中心(CDC)确诊的HIV感染者及30例健康体检者血液和尿液标本同时进行HIV-1抗体检测;以确认结果为准,计算尿液HIV-1抗体检测的敏感度、特异度。结果 59例经CDC确诊的HHIV感染者血清HIV-1抗体全部阳性,相应尿液中HIV-1抗体阳性53例,阴性6例;对照组30例的血清HIV-1抗体全部阴性,相应尿液1例HIV-1抗体阳性,经血清ELISA法及胶体硒法对该样本进行HIV-1抗体检测均阴性。以确认结果为准,尿液HIV-1抗体检测阳性敏感度为89.83%,特异度为96.67%。结论在采集血液标本不便的情况下,可通过检测尿液HIV-1抗体对高危人群进行HIV感染筛查。     

一种血液艾滋病病毒抗体免疫印迹试剂的现场评估

目的对Cambridge血液艾滋病病毒（HIV）-1抗体免疫印迹（WB）试剂进行现场评估并考核其在不同的HIV感染状态的人群中确认试验检测的敏感性和特异性.方法选取不同的现场,分别采集不同的HIV感染状态人群的血液样品,共计645份.经酶联免疫吸附试验（ELISA）检测后,分别使用Cambridge血液HIV-1抗体WB试剂盒和HIV blot 2.2 HIV-1/2型WB确认试剂盒进行平行对比试验.结果在已知既往HIV感染者中,Cambridge血液WB与Genelabs WB检测结果均为阳性,在此人群中上述2种确认试剂的敏感性均为100%.在398例HIV抗体ELISA检测为阴性的人群中,Cambridge血液WB试验23例为不确定;Genelabs血液WB试验86例为不确定,在此类人群中上述2种确认试剂的特异性分别为94.22%（375/398）和78.39%（312/398）.结论Cambridge血液HIV-1抗体WB试剂盒与Genelabs诊断公司的HIV blot 2.2 HIV-1/2型WB试剂盒的试验结果对比,在特异性方面前者优于后者.     

免疫印迹法检测血液和尿液中HIV-1抗体的实验研究

目的 用免疫印迹法检测HIV携带者的血液和尿液样本,研究尿检试剂替代血检试剂用于HIV确证的可行性.方法 采集河南、浙江研究对象87名的血液和尿液,分别用血检试剂和尿检试剂平行检测,按各自检定标准判定结果,统计各特异性条带出现频率.结果 87名被检者中,血检阳性41人,尿检阳性39人,符合率为97.7%.阳性血液样本中出现频率最高的条带是gp160、p24、gp120,最低的是p55、p31、p17;阳性尿液样本中出现频率最高的条带是gp160、gp120、sp41,最低的是p17、p55、p24.结论 HIV携带者尿液中的抗体与血液不同,灵敏度也有一定差异,通过改进尿检试剂的制备工艺,同时制定适宜的判定标准,可以使尿检试剂替代血检试剂应用于HIV-1抗体的检测确证.     

某种人类免疫缺陷病毒Ⅰ型核酸定量检测试剂盒的性能评估

目的对某种人类免疫缺陷病毒Ⅰ型（HIV-1）核酸定量检测试剂盒（PCR-荧光探针法）的临床应用性能进行评估。方法收集不同HIV感染状态人群的血液样品共计109份,分别使用HIV-1被评估试剂与参比试剂的核酸定量检测试剂盒进行平行对比试验。统计学处理使用Kappa值、R2和Bland-Altman模型。结果被评估试剂检测结果相对于参比试剂,检测结果的总符合率为97.25%（95%CI:92.17%～99.43%）,Kappa值为0.92（P<0.001）,一致性强度为最强。109例样本中,均在被评估试剂与参比试剂定量检测范围内的样本为84例,两种试剂盒检测结果的回归分析表现出较强的相关性（R2=0.853 6）。使用Bland-Altman模型比较两种试剂检测结果的差异均值,结果显示对于未进行抗病毒治疗的HIV感染者样本两种试剂检测结果具有较好的一致性。结论被评估试剂和参比试剂对同一份血浆样本检测结果具有较好的定性符合程度和较强的相关性,对HIV感染者样本两试剂检测结果有较强的定量一致性。     

使用HIV初筛方法定性判断的可行性研究

目的分析使用胶体金免疫层析法(金标法)和酶联免疫法(ELISA)试验定性判断HIV抗体检测结果的可行性。方法以凉山州越西县全人群体检HIV快速检测阳性者为研究对象,分两组分别进行3次金标法和ELISA法检测,将检测至少1次阳性样本进行HIV抗体确证检测(免疫印迹法WB),分析确证结果与3次筛查结果一致性。结果共收集样本1 181例,金标法和ELISA法试验组分别为459例和722例,金标法检测3次均阳性样本数450例,其中449例(99. 78%) WB法为HIV-1抗体阳性,1例WB法为HIV-1抗体不确定,经随访为HIV抗体阴性,并且该样本金标法反应强度与HIV-1抗体阳性样本反应强度较接近; ELISA法检测3次均阳性样本数703例,其中701例(99. 72%) S/CO平均值≥6,且WB法为HIV-1抗体阳性。结论使用ELISA法检测HIV抗体时,结合检测阳性次数与S/CO平均值可定性判断HIV抗体检测结果。     

某种人类免疫缺陷病毒I型核酸定量检测试剂盒的性能评估

目的对某种人类免疫缺陷病毒I型（HI-1）核酸定量检测试剂盒（PCR．荧光探针法）的临床应用性能进行评估。方法收集不同HIV感染状态人群的血液样品共计109份,分别使用HIV-1被评估试剂与参比试剂的核酸定量检测试剂盒进行平行对比试验。统计学处理使用Kappa值、砰和Bland—Ahman模型。结果被评估试剂检测结果相对于参比试剂,检测结果的总符合率为97．25％（95％CI：92．17％-99．43％）,Kappa值为0．92（P〈0．001）,一致性强度为最强。109例样本中,均在被评估试剂与参比试剂定量检测范围内的样本为84例,两种试剂盒检测结果的回归分析表现出较强的相关性（R2=0．8536）。使用Bland—Altman模型比较两种试剂检测结果的差异均值,结果显示对于未进行抗病毒治疗的HIV感染者样本两种试剂检测结果具有较好的一致性。结论被评估试剂和参比试剂对同一份血浆样本检测结果具有较好的定性符合程度和较强的相关性,对HIV感染者样本两试剂检测结果有较强的定量一致性。     

几种国产HIV抗体酶免法检测试剂的质量评价

目的 考察国产艾滋病抗体酶免法试剂盒的质量，为部队选择质量好的艾滋病诊断试剂盒提供依据。方法 对7种主要的国产人免疫缺陷病毒(HIV)抗体酶免法试剂盒进行质量考核。以1种进口HIV抗体酶免法试剂为参比试剂，用7种考评试剂对300份血清标本进行了统一的检测。300份血清标本都经过免疫印迹方法确认，其中包括国家艾滋病参比实验室提供的50份血清和本实验室的250份血清。结果 参比试剂可以检测出全部125份阳性血清，敏感性为100％；国产试剂A、B、C、D和E可以检测出全部125份阳性血清，敏感性为100％；国产试剂F和G可以检测出124份阳性血清，敏感性为99．3％。在153份阴性血清中，参比试剂将1份错判为阳性，特异性为99．3％。国产考评试剂有1-6份错判为阳性，特异性为96．1％。99．3％。结论 国产酶免疫法HIV抗体检测试剂大部分已经达到或接近进口试剂质量水平，可以作为部队艾滋病初筛试验的诊断试剂盒。     

部分国产艾滋病病毒抗体检测试剂临床应用质量评价

目的　为掌握国产艾滋病病毒（ＨＩＶ） 抗体筛选酶免试剂的实际应用状况,对８ 种主要的国产ＨＩＶ抗体筛选酶免试剂进行了临床应用质量评价。方法　以一种进口ＨＩＶ 抗体筛选酶免试剂为参比,用８ 种考评试剂对２００ 份标本进行了统一的检测。２００ 份标本包括１００ 份经过确认的ＨＩＶ抗体阳性、阴性、可疑标本和１００ 份新疆吸毒人群的血清标本。结果　参比试剂可以检出全部７４ 份阳性标本,敏感性为１００ ％ ,而考评试剂有６ ～１８ 份不等的假阴性结果,敏感性为８１．１％ ～９１．９％ 。假阴性结果主要发生于来自吸毒人群的ＨＩＶ 抗体弱阳性标本。考评试剂的特异性相对较好,在１０７ 份阴性标本中,参比试剂将２ 份错判为阳性,特异性为９８ ．１ ％ ,考评试剂有０～８ 份标本错判为阳性,特异性为９２．５ ％ ～１００％ 。结论　考评试剂的主要问题是敏感性低,这可能与检测原理是间接法、抗原组成不全面、反应条件不合理等因素有关。     

四种艾滋病病毒抗体筛查试剂检测性能评价

目的 通过对比分析艾滋病病毒(HIV)抗体筛查阳性结果与免疫印迹试验(WB)结果,评价4种HIV抗体筛查试剂检测性能.方法 2004年1月至2009年6月,分别用中山生物工程有限公司、荷兰生物梅里埃有限公司、珠海丽珠有限公司生产的3种酶联免疫吸附试验(enzyme linked immunasorbent assay,ELISA)试剂初筛血清HIV抗体,用美国雅培Determine HIV-1/2胶体硒标试剂、原试剂复检.筛查阳性样本用WB法进行确认.结果 共检测206 151例患者血清HIV抗体,确认HIV抗体阳性193例(0.094%).3种ELISA试剂敏感度、阴性预期值均为100%;雅培试剂分别为93.93%、91.67%,其漏检的样本均为WB不确定.中山、梅里埃、丽珠、雅培试剂的特异度分别为99.88%、99.89%、99.96%、89.38%;阳性预期值(study predictive value of a positive test result,PVP)分别为35.58%、46.46%、76.61%、92.20%;功效分别为99.88%、99.89%、99.96%、91.98%;3种ELISA试剂ROC曲线下面积分别为0.93、0.99、0.95.丽珠的PVP明显高于中山(X~2=45.804,P=0.000)、梅里埃(X~2=25.231,P=0.000);梅里埃的PVP比中山高,但无统计学意义(X~2=2.488,P=0.115);雅培PVP最高(与丽珠相比,X~2=18.633,P=0.000).在WB确认阳性、不确定、阴性组,均存在S/CO值[样本(sample)吸光度值/临界值(cut off)]＜6或≥6的样本.中山试剂确认阳性组S/CO值(14.29±2.63)明显高于阳性-阴性组(2.80±3.25)(t=17.652,P=0.000).梅里埃试剂确认阳性组S/CO值(16.09±2.35)明显高于阳性-阴性组(2.14±1.91)(t=31.622,P=0.000).丽珠试剂确认阳性组S/CO值(11.54±1.95)明显高于阳性-不确定组(5.54±3.57)(t=6.386,P=0.000)、阳性-阴性组(3.25±2.41)(t=21.772,P=0.000);阳性-不确定组S/CO值则高于阳性-阴性组(t=2.301,P=0.033).结论 4种筛查试剂性能良好,根据S/CO值不能准确估计WB确认结果,筛查阳性后必须进行确认.     

Serological diagnosis of human immuno-deficiency virus in Burkina Faso: reliable, practical strategies using less expensive commercial test kits.

Reported are the results of a cross-sectional survey in Burkina Faso to identify reliable, practical strategies for the serological diagnosis of HIV-1 and/or HIV-2 infections, using less-expensive commercial test kits in various combinations, as an alternative to the conventional Western blot (WB) test, which costs US$ 60. Serum samples, collected from blood donors, patients with acquired immunodeficiency syndrome (AIDS) and pregnant women, were tested between December 1995 and January 1997. Twelve commercial test kits were available: five Mixt enzyme-linked immunosorbent assays (ELISA), three Mixt rapid tests, and four additional tests including monospecific HIV-1 and HIV-2 ELISA. The reference strategy utilized a combination of one ELISA or one rapid test with WB, and was conducted following WHO criteria. A total of 768 serum samples were tested; 35 were indeterminate and excluded from the analysis. Seroprevalence of HIV in the remaining 733 sera was found to be 37.5% (95% confidence interval: 34.0-41.1). All the ELISA tests showed 100% sensitivity, but their specificities ranged from 81.4% to 100%. GLA (Genelavia Mixt) had the highest positive delta value, while ICE HIV-1.0.2 (ICE) produced the most distinct negative results. Among the rapid tests, COM (CombAIDS-RS) achieved 100% sensitivity and SPO (HIV Spot) 100% specificity. Various combinations of commercial tests, according to recommended WHO strategies I, II, III, gave excellent results when ICE was included in the sequence. The best combination of tests for strategy II, which achieved 100% sensitivity and specificity, was to use ICE and COM, the cost of which was US$ 2.10, compared with US$ 55.60 for the corresponding conventional strategy. For strategy III, the best combination, which achieved 100% sensitivity and specificity, was to use ICE, ZYG (Enzygnost Anti HIV-1/HIV-2 Plus) and COM, the cost of which was US$ 2.90 (19.2 times lower than the corresponding strategy requiring WB). No rapid test combination showed 100% sensitivity and specificity. Our results indicate that the serodiagnosis of HIV in Burkina Faso is possible by using reliable, less-expensive strategies which do not require Western blot testing. Moreover, there is a choice of strategies for laboratories working with or without an ELISA chain.     

Potential shortage of supplemental test kits for detecting HIV-1 antibodies

The Public Health Service has become aware of a potential shortage of supplemental test kits used for confirmatory testing of human immunodeficiency virus (HIV) antibodies in specimens obtained from either patients or blood and plasma donors. On April 17, 2002, Calypte Biomedical Corporation (Alameda, California) announced the company might stop manufacturing the Cambridge Biotech HIV-1 Western blot kit. The distributor, bioMérieux, Inc. (Durham, North Carolina), immediately notified customers that it no longer would be able to distribute the Cambridge Biotech HIV-1 Western blot kit.     

艾滋病病毒抗体初筛诊断试剂临床质量评估

目的：了解目前市场供应的艾滋病病毒(HIV)抗体初筛试剂的质量及使用情况。方法：对5种HIV抗体酶联免疫吸附试验(ELISA)诊断试剂用200份血清样品进行统一测试。200份血清标本包括100份经过确认的HIV抗体阳性、弱阳性、阴性标本及100份高危人群血清标本初筛阳性或可疑标本再用免疫印迹法(WB)做确认对比分析。结果：5种参评试剂的敏感性为96．88％--100．00％，特异性为97．02％--100．00％，假阳性率为0--2．98％，假阴性率为0--3．13％，功效率为97．00％--100．00％，阳性预测值为86．11％--100．00％，阴性预测值为99．39％--100．00％。结论：随着第三代ELISA抗体诊断试剂的发展，试剂的质量较之以前已有了明显的提高。     

6种人类免疫缺陷病毒(HIV)抗体初筛试剂质量评估

[目的]评估国内临床试剂市场中流通的部分HIV抗体初筛试剂的质量。[方法]分别用5种HIV抗体ELISA检测试剂和1种HIV抗体快速诊断试剂对100份已知结果样品和100份未知结果样品的进行检测，初筛结果阳性或可疑阳性的样品用蛋白印迹法（WB）确认。根据检测结果，计算各被评估试剂的质量性能指标。[结果]5种酶标试剂的综合质量性能指标（功效率）均等地或大于96.5%。部分国产试剂的质量性能指标已经接近国际先进产品的水平，但仍有个别国产试剂存在较为严重的漏检问题，假阴性率超过9.09%。HIV快速诊断试剂与ELISA试剂相比，仍存在差距。[结论]本次所评估的5种ELISAHIV抗体初筛试剂在综合质量性能指标（功效率）上优于快速诊断试剂，所评估的进口试剂仍领先于国内同类产品。国产试剂的总体质量虽已有所提高，但加强对国产试剂质量管理和监督机制的建设仍不容忽视。     

三种HIV抗体确证试剂盒检测早期感染的比较

目的 比较3种HIV抗体确证试剂盒检测HIV早期感染的性能.方法 对5份HIV抗体阳性血浆样品进行10倍系列稀释,然后用ELISA检测.对检测结果呈阳性反应的稀释样品分别用3种HIV抗体确证试剂盒进行检测以测试其灵敏度,所用试剂盒包括北京万泰公司的HIV 1+2型抗体检测试剂盒(万泰RIBA)、新加坡MP公司的HIV 1+2型抗体检测试剂盒(MP-WB)和比利时Innogenetics公司的INNO-LIA TM HIV Ⅰ/ⅡScore(INNO-LIA).用这些试剂盒检测11套HIV抗体阳转血清盘中ELISA试验呈阳性反应的样品(共48份).结果 对HIV抗体阳性稀释样品的检测结果显示,当5份样品在稀释100倍时,万泰RIBA均检测出阳性结果.在ELISA试验呈阳性反应的48份HIV抗体阳转血清盘样品中,万泰RIBA、MP-WB和INNO-LIA的确证阳性率分别为97.92%(47/48)、81.25%(39/48)和91.67%(44/48).万泰RIBA与MP-WB之间差异有统计学意义(χ2=6.13,P＜0.05),INNO-LIA与MP-WB之间差异有统计学意义(χ2=5.48,P＜0.05),而万泰RIBA与INNO-LIA之间差异无统计学意义(χ2=1.33,P＞0.05).对于含有HIV抗体检测结果不确定样品的6套阳转血清盘,用万泰RIBA、MP-WB和INNO-LIA检测的平均阳转时间分别为0.7、13.3、3.7 d.结论 与我国目前常用的MP-WB相比,万泰RIBA和INNO-LIA可以缩短HIV抗体确证的窗口期.

Abstract：

Objective This study was to compare the performance of three HIV antibody confirmatory assay kits in confirming early HIV infection. Methods Five HIV antibody-positive plasma specimens were ten-fold serially diluted and then detected by ELISA. The above diluted specimens were detected with the following three HIV antibody coufirmatory assay kits to analyze their sensitivity, including Wantai-RIBA ( Recombinant immunoblot assay, Beijing Wantai Biological Pharmacy, China), MP-WB ( HIV Blot 2. 2 WB,MP Biomedicals Asia Pacific Pte. Ltd. ,Singapore) and INNO-LIA ( INNO-LIATM HIV Ⅰ/Ⅱ Score, Innogenetics N. V. , Belgium), respectively. These kits were further used to detect 48 ELISA-reactive specimens from 11 sets of HIV seroconversion specimens (a total of 48 sanples ) which were previously detected as HIV antibody-positive by ELISA. Results When 5 samples were diluted to 100 fold,Wantai-RIBA still can detect them positive. Among the 48 HIV antibody-positive specimens detected with ELISA,the confirmation positive rate for Wantai-RIBA, MP-WB and INNO-LIA were 97.92% (47/48),81.25 % ( 39/48 ) and 91.67% ( 44/48 ), respectively. There was statistically significant difference between the confirmatory results of Wantai-RIBA and MP-WB ( χ2 = 6. 13, P ＜ 0. 05 ), as well as between those of INNO-LIA and MP-WB ( χ2 = 5.48, P ＜ 0. 05 ); however, there was no statistically significant difference between those of Wantai-RIBA and INNO-LIA ( χ2 = 1.33, P ＞ 0. 05 ). For other six HIV seroconversion panels containing indeterminate specimens, the average seroconversion period of time for Wantai-RIBA,MP-WB and INNO-LIA were 0. 7,13.3 and 3.7 days, respectively. Conclusion Compared with MP-WB,Wantai-RIBA and INNO-LIA could reduce the window period to confirm early HIV infection.     

Evaluation of a panel of commercial kits for the detection of serum HIV-specific antibodies, and choice of alternative strategies for the serological diagnosis in Libreville (Gabon)

Nine commercially available kits for the screening of serum antibodies to the human immunodeficiency virus (HIV) were evaluated with a panel of 170 serum samples from adults in Gabon. The reference procedures showed that 96 samples had no antibodies, while 74 produced antibodies to HIV-1 (n=72) or HIV-2 (n=2). The sensitivity for 2 kits was less than 99% and the specificity of 3 less than 95%. Based on the panel of Gabonese serum samples, 4 of the 9 kits met the World Health Organization (WHO) acceptability criteria: sensitivity greater than 99% and specificity greater than 95%. Three kits available in Gabon that met these criteria were finally retained: Determine HIV-1/2, Genscreen Plus HIV Ag-Ab, and Immunocomb II HIV1&2 BiSpot. Of 18 configurations of alternative diagnosis strategies for HIV infection with these three kits, some WHO strategy II configurations (2 sequential assays) and all the WHO strategy III configurations (3 sequential assays) provided the maximum accuracy in diagnosing HIV infection in Gabon (sensitivity, specificity, positive predictive value, negative predictive value of 100%). The configuration using the Determine HIV-1/2 kit as first screening assay, followed by Genscreen Plus HIV Ag-Ab as a confirmatory assay, and finally, Immunocomb II HIV1&2 BiSpot as the third assay to discriminate samples discordant with the two first assays, was best, with high accuracy and less expense. The configuration of the two sequential rapid assays, Immunocomb II HIV1&2 BiSpot followed by Determine HIV-1/2, was also very accurate and reliable, as well as easiest to carry out (no need for ELISA technology), but it was twice as expensive as the first configuration with three sequential kits. In conclusion, when the laboratory facilities are available, the sequential diagnostic strategy of two rapid assays and a combined ELISA assay constitutes the best configuration, in terms of both accuracy and cost. When laboratory facilities are unavailable, sequential use of two rapid assays constitutes a convenient and accurate configuration, but is much more expensive.