危险因素记分法筛查无症状糖尿病患者分析

目的建立一种适合、经济和有效的无症状糖尿病的筛检方法。方法在上海市某郊区2008～2009年2型糖尿病流行病学调查的基础上,分别选择两组人群进行危险因素记分法及其应用价值研究。人群A采用Logistic回归分析筛选糖尿病的危险因素,根据危险因素的OR值确定不同变量的记分值;人群B以累计记分值的大小判断个体患病的危险性,并验证该方法进行人群筛检的真实性和有效性。结果当以累计记分值为16作为判别阈值时,该方法对人群中无症状糖尿病筛检的灵敏度和特异度分别为65.85%和57.34%,阳性预测值为11.69%。结论与筛查糖尿病患者的金标准相比,危险因素记分法筛检无症状糖尿病患者简便、易行、经济,可作为糖尿病人群筛查的第一线方法。     

糖尿病危险因素评分量表在社区人群糖尿病筛检中的应用

目的探讨糖尿病危险因素评分量表在社区人群糖尿病筛检中的应用。方法通过昆明市居民糖尿病流行病学调查,建立人群危险因素的记分方法,采用Logistic回归分析筛选糖尿病危险因素,根据危险因素的OR值,计算个体累计分值,以判断个体患病危险性,并用于对试点社区人群的筛查,以验证该方法筛检的真实性和可靠性。结果多因素分析(P<0.05)显示,以父母或直系兄弟姐妹患糖尿病、年龄超过45岁、患有高血压、患有高血脂、体质指数在24.0～27.9之间、体质指数>28.0、腰臀比例>0.9(男)或>0.85(女)、最近有多饮多尿症状、最近乏力体重明显下降和很少进行体育锻炼为变量作为主要危险因素记分,其累计分值越高,表明人群中无症状糖尿病的患病风险越大。当以7为阈值的时候,其灵敏度为69.6%,特异度为60.0%,提示:只要对40.0%的社区居民进行筛查就可以查出全人群中69.6%的未发现的糖尿病患者。结论危险因素记分法在实际工作中有较大的应用价值,可作为社区居民糖尿病筛查的第一线方法,并可在社区糖尿病预防控制工作中广泛应用。     

健康体检人群糖尿病发病风险的评估方法

目的建立适合健康体检个体糖尿病发病风险的评估方法。方法结合国内外的研究结果分析近年糖尿病发病率资料及发病风险因素,得出我国成年人糖尿病发病的主要风险因素,将目标人群随机分为两组队列,队列1用于危险因素评分方法的建立,采用非条件logistic回归分析筛选糖尿病的危险因素,根据危险因素的回归系数确定不同变量的积分值,以累计积分值的大小判断个体患病的危险性,并以队列2的资料验证该方法进行人群筛检的价值。结果研究结果表明男性与女性分别当积分值为65．0与65．5时,约登指数最大,故将65．0与65．5作为判别不同性别发生糖尿病风险的阈值,其筛检的灵敏度分别为90．6％与83．3％,特异度分别为89．4％与97．7％,阳性预测值分别为58．8％与80．0％,阴性预测值为98．3％与98．2％。曲线下面积分别为0．955与0．899,危险因素评分法用于筛查糖尿病,差异有统计学意义（P=0．000）。结论该方法简易经济,可操作性强,有望成为健康体检机构筛查人群糖尿病发病的高危人群的实用、有效的方法。     

无症状糖尿病不同筛查方法效果评价

目的建立一种适合上海市社区居民经济有效的无症状糖尿病人群筛查方法.方法在上海市社区人群糖尿病流行病学调查基础上,选择目标人群进行危险因素记分法及Logistic回归模型法.训练组用于危险因素记分法及Logistic回归模型法的建立,采用Logistic回归分析筛选糖尿病危险因素,根据危险因素的OR值及β值,计算个体累计分值和发病概率,以测试组的资料验证2种方法进行人群筛查的真实性和可靠性,并对2种方法的效率和效益进行比较.结果当以累计分值为18作为判别的阈值时,危险因素记分法的灵敏度为61.22%,特异度为80.40%.当以累计发病概率0.05作为判别的阈值时,Logistic回归模型法的灵敏度为67.35%,特异度为76.19%.结论2种筛查方法在筛查效果上差异无统计学意义.但是,危险因素记分法在实际工作中具有较大的应用价值,可作为糖尿病人群筛查的第一线方法.     

胰岛素非依赖型糖尿病人群筛检的数量化方法

在人群的胰岛素非依赖型糖尿病（ＮＩＤＤＭ）危险因素病例对照研究的基础上，应用模糊数学的原理和方法，通过对糖尿病有关影响因素的数量化，建立了用于人群筛检的数学模型，对８７３４名２０～７４岁自然人群为研究对象的实际应用结果表明，随着数量化方法的隶属度（ＡＤ）值的增加，人群中糖尿病的患病风险亦随之增高，当判别阈值定为０．３时，对人群中既往糖尿病和新诊断糖尿病判别的灵敏度分别为７１．２６％和６０．９８％，特异度为７２．０７％。本法简便，易行，经济，有利于获得满意的受检率，可用于个体和群体（社区）的患病危险度测定及健康教育，有望成为糖尿病人群筛检的有效和实用的方法     

糖尿病高危人群风险因素对照研究

目的 分析糖尿病有关危险因素间的差异显著性。方法 2003名无症状,但有明确糖尿病危险因素,包括家族糖尿病史、肥胖、高血压、高血脂、女性巨大胎儿史为筛检对象。来自相同社区无糖尿病危险因素的5362人作为对照。结果 接受筛检的2003人中,131人被诊断有糖尿病,占6.54％。在上述人群中,有1种糖尿病危险因素的为1547人,占77.23％;有2种危险因素的为387人,占19.27％;有3种以上危险因素的70人,占3.49％。对照组5362人中,96人被诊断有糖尿病,占1.79％。和对照组相比,有明显危险因素的2003人在年龄标化后患糖尿病的OR值(95％CI)为2.68(2.20～3.25)。有1种危险因素的人患糖尿病的OR值为2.89,而有3种以上危险因素的OR值则增加到4.68。结论 高危人群罹患糖尿病的风险和具备危险因素量呈正相关,有必要在这些高危人群中开展早期、规则的糖尿病筛检。     

胃癌个体危险度及人群筛检数量化评价的研究

目的：建立胃癌个体危险度判定及人群筛检的数量化模型。方法：在人群为基础的胃癌危险因素病例对照研究的基础上筛选出有统计学意义变化，应用概率论、模糊数学等原理和方法对胃癌危险因素和保护因素数量化，建立用于个体胃癌危险度测量和人群筛检的数量化评价方法（数学模型）。采用两种不同的加权系数计算方法，分别确定该数量化方法的判别阈值为0．20和0．17，对63例胃癌患者和693名正常人进行实际判别。结果：灵敏度和特异度均分别达到69％和63％左右，加权系数计算方法不同并不影响实际判别效果。结论：建立的胃癌个体危险度及人群筛检的数量化模型灵敏度和特异度尚理想；方法简便、易行、经济，有利于获得满意的受检率；可用于个体和群体（社区）的胃癌危险度测定。     

无锡市城区社区自然人群糖尿病及其患病风险现况

目的了解无锡市城市社区自然人群糖尿病及其患病风险现状。方法采用多阶段整群随机抽样法抽取无锡市城区社区20岁以上居民13 575人进行现况调查。结果无锡市城区社区20岁以上自然人群糖尿病和空腹血糖受损现患率分别为6.27%和1.77%;年龄、糖尿病家族史、超重或肥胖、高血压、血脂异常为该地区糖尿病的危险因素;超重或肥胖、高血压、血脂异常的暴露率在男性中分别为38.89%,40.54%和48.27%,女性中分别为33.43%,31.62%和42.72%;人群中至少具有上述一项危险因素的个体占86.71%,具有高度、中度糖尿病综合患病风险的个体在人群中占25.22%。结论无锡市城市社区人群糖尿病及其患病风险处于较高水平,需大力加强糖尿病与其他慢性非传染性疾病的预防和控制。     

痰液细胞图像分析法筛检锡矿接尘工人肺癌的方法学评价

目的 评价痰液细胞图像分析对锡矿接尘工人肺癌的筛检试验,分析影响锡矿肺癌高危人群发病的危险因素.方法 1998年用单纯随机抽样的方法选取广西某锡矿队列中45岁以上的男性接尘矿工345人为研究对象,采用全自动细胞图像分析法用经验指标(痰液)对研究对象进行肺癌筛检,其后追访该人群至2006年.以临床确诊为金标准,用筛检试验方法评价痰液细胞图像分析对锡矿接尘工人肺癌的筛检效能及最佳工作点.结果 追访期间,共确诊11例肺癌病例;除年龄和职业接触外,吸烟是锡矿高龄接尘工人肺癌发病的危险因素(P=0.0384),调整混杂因素后,高吸烟组的相对危险度为18.21(2.15～154.39).细胞图像分析法经验筛检指标的灵敏度、特异度和正确指数分别为27.3%、83.5%、10.8%;经拟合受试者工作特征(ROC)曲线,C2.5(DNA指数介于1.25～2.50之间所占百分比)以1.70%为最佳工作点,痰液细胞图像系统检测的灵敏度、特异度、一致率、阳性预测值、阴性预测值和正确指数分别为72.7%、62.3%、62.6%、6.0%、98.6%、35.0%.结论 吸烟是高龄接尘工人肺癌的危险因素;使用痰液细胞图像分析法,将指标C2.5的筛检值调整为1.70%,有助于早期发现锡矿高危人群中的可疑肺癌患者.     

重庆社区居民糖尿病相关危险因素定量评价标准

目的 探讨重庆市16岁以上社区居民糖尿病相关危险因素,制定危险因素的定量评价模型,为预测个体糖尿病的患病危险奠定基础.方法 采用病例对照研究的方法,从重庆市沙坪坝、小龙坎、天星桥、渝碚路、磁器口5个社区中以1:2的比例抽取糖尿病患者1981例,健康人群3962例进行回顾性调查,利用logistic回归方法分析,得出各危险因素与糖尿病的OR值,运用统计模型将不同暴露水平的危险因素转化成危险分数.结果 得到不同性别、年龄、行为、疾病以及家族史的个体在不同情况下的危险分数,男性为高脂血症史(14.995)、冠心病(6.689)、高血压家族史(4.005)、吸烟(3.111)等13个危险因素进入主效应模型;女性为高脂血症史(12.426)、高血压家族史(3.986)、脑卒中史(2.714)、嗜甜食(1.244)等15个危险因素.根据个体情况得到组合危险分数,从而预测该个体的糖尿病发病危险.结论 改变不良的生活方式以及个人疾病的积极治疗和控制,能有效降低糖尿病的发病率;而根据危险因素建立的危险分数评估模型是健康教育的有力依据,也是当前开展社区卫生服务的重要方法.     

Screening for diabetes in France: data from the 2000-2001 cohort of the national medical insurance system

BACKGROUND: Type 2 diabetes mellitus may go undiagnosed for several Years while complications are silently developing. In France, from 2 to 3.7% of adults aged 35-65 are unaware they have diabetes. Nevertheless fasting serum glucose is a simple diagnostic test. METHODS: We described people who underwent opportunist diabetes screening (serum glucose) within 2 Years (2000-2001). We used the administrative EPAS cohort from the employee National Health Insurance System which covers 70% of the total population in France. The data are based on reimbursements of glucose testing and hospitalization among people who did not received reimbursements of treatment for diabetes but used medical services during the 2 Years. RESULTS: The opportunistic screening rate within 2 Years was 48.6% overall and increased with age. Among those 45 Years old or older, it was 71.2%. The screening rate was higher among women than men. CONCLUSION: Opportunistic screening for diabetes is commonly practised in France, despite the lack of official guidelines. Several hypotheses may explain the discrepancy between common opportunist screening and high prevalence of undiagnosed diabetes: 1). undiagnosed diabetes is mostly present in people who do not use medical services; 2). opportunistic screening is not performed among the most at-risk population; 3). testing is not performed on fasting samples or results are neglected; 4). results of testing are overlooked by doctors/patients; 5). epidemiological studies based on self-report of diagnosis and only one testing overestimate undiagnosed diabetes.     

Annals Journal Club: Yield of Opportunistic Targeted Screening for Type 2 Diabetes in Primary Care: The Diabscreen Study

PURPOSE In screening for type 2 diabetes, guidelines recommend targeting high-risk individuals. Our objectives were to assess the yield of opportunistic targeted screening for type 2 diabetes in primary care and to assess the diagnostic value of various risk factors.METHODS In 11 family practices (total practice population = 49,229) in The Netherlands, we conducted a stepwise opportunistic screening program among patients aged 45 to 75 years by (1) identifying high-risk individuals (=1 diabetes risk factor) and low-risk individuals using the electronic medical record, (2) obtaining a capillary fasting plasma glucose measurement, repeated on a separate day if the value was greater than 110 mg/dL, and (3) obtaining a venous sample if both capillary fasting plasma glucose values were greater than 110 mg/dL and at least 1 sample was 126 mg/dL or greater. We calculated the yield (percentage of invited patients with undiagnosed diabetes), number needed to screen (NNS), and diagnostic value of the risk factors (odds ratio and area under the receiver operating characteristic curve).RESULTS We invited for a first capillary measurement 3,724 high-risk patients seen during usual care and a random sample of 465 low-risk patients contacted by mail. The response rate was 90% and 86%, respectively. Ultimately, 101 high-risk patients (2.7%; 95% confidence interval [CI], 2.2%–3.3%; NNS = 37) and 2 low-risk patients (0.4%; 95% CI, 0.1%–1.6%; NNS = 233) had undiagnosed diabetes (P <.01). The prevalence of diabetes among patients 45 to 75 years old increased from 6.1% to 6.8% as a result. Among diagnostic models containing various risk factors, a model containing obesity alone was the best predictor of undiagnosed diabetes (odds ratio = 3.2; 95% CI, 2.0–5.2; area under the curve=0.63).CONCLUSIONS The yield of opportunistic targeted screening was fair; obesity alone was the best predictor of undiagnosed diabetes. Opportunistic screening for type 2 diabetes in primary care could target middle-aged and older adults with obesity.     

Diabetes Prevalence and its Risk Factors in Rural Area of Tamil Nadu

Objective:

To estimate the usefulness of the Indian diabetes risk score for detecting undiagnosed diabetes in the rural area of Tamil Nadu.

Materials and Methods:

The present study was conducted in the field practice area of rural health centers (Chunampett and Annechikuppam, Tamil Nadu), covering a population of 35000 from February to March 2008 by using a predesigned and pretested protocol to find out the prevalence and the risk of diabetes mellitus in general population by using Indian diabetes risk score.

Results:

1936 respondents comprising 1167 (60.27%) females and 769 (39.73%) males were studied. Majority 1203 (62.50%) were Hindus. 1220 (63.%) had studied up to higher secondary. 1200 (62%) belonged to lower and lower-middle socio-economic class. A large number of the subjects 948 (50%) were below 35 years of age. Most of the respondents 1411 (73%) indulged in mild to moderate physical activity. 1715 (87.91%) had no family history of diabetes mellitus. 750 (39.64%) individuals were in the overweight category (>25 BMI). Out of these overweight persons, 64% had high diabetic risk score. It is observed that chances of high diabetic score increase with the increase in BMI. Prevalence of diabetes in studied population was 5.99%; out of these, 56% known cases of diabetes mellitus had high (>60) IDRS. Co-relation between BMI and IDRS shows that, if BMI increases from less than 18.50 to more than 30, chances of high risk for developing diabetes mellitus also significantly increase.

Conclusions:

This study estimates the usefulness of simplified Indian diabetes risk score for identifying undiagnosed high risk diabetic subjects in India. This simplified diabetes risk score has categorized the risk factors based on their severity. Use of the IDRS can make mass screening for undiagnosed diabetes in India more cost effective.     

An evaluation of the Nashville REACH 2010 community health screening strategy

Community-based screening is 1 of 4 strategies selected by the Nashville REACH 2010 project for reducing disparities in heart disease and diabetes among African Americans in North Nashville, Tenn. We evaluated our screening efforts by asking 4 questions: (1) Are the screening participants representative of the target population? (2) How often were screening participants with possible undiagnosed hypertension, high cholesterol, and diabetes identified? (3) How often were screening participants with an elevated risk for developing hypertension, high cholesterol, and diabetes identified? and (4) How often did we identify screening participants with known hypertension, high cholesterol, and diabetes whose disease management was suboptimal? Results from 1757 persons screened were compared to telephone surveys from 16,199 Nashville residents. Those screened were younger and healthier than the target population. Rates of potentially undiagnosed cases among African Americans were 0.8% for diabetes, 17.4% for hypertension, and 32.7% for high cholesterol. High-risk individuals were identified 13.1% of the time for diabetes, 45.3% of the time for hypertension, and 21.3% of the time for total cholesterol. Rates of poorly controlled known disease were 23.5% for diabetes, 39.0% for hypertension, and 58.2% for total cholesterol. Although we reached a younger and healthier group than the community population, community-based screenings identified many people with potential health risks. We present a model of how to organize and implement successful community-based screening.     

Predictive genetic screening for type-1 diabetes in the Hungarian population

INTRODUCTION: In the modern genetic era the principles of genetic screening are being changed. In addition to diagnostic screening for rare monogenic diseases, predictive screening for common polygenic conditions, like type 1 diabetes, will be more widely implemented. The majority of the genetic background of type 1 diabetes is encoded by the HLA DQ and DR genes, selected variants of which could be used as screening markers. However, risk conferred by various HLA genotypes shows considerable ethnic variation, therefore population-specific screening markers need to be established. AIMS: The aim of this study was to describe a screening strategy based on risk-defining HLA DRB1-DQA1-DQB1 markers to identify individuals at risk for type 1 diabetes in the Hungarian population. METHODS: HLA genotypes of 149 consecutively diagnosed children with type 1 diabetes (age at diagnosis 0-14, mean 8.8 +/- 4.2 years) and 177 randomly selected healthy schoolchildren were studied. Allele-specific polymerase chain reaction method was used for HLA typing. The diagnostic sensitivity, specificity and predictive value of diabetes associated DRB1-DQA1-DQB1 alleles were analysed in a step-wise strategy. RESULTS: The highest diagnostic sensitivity was detected when DQB1 typing was complemented by DQA1 typing on DQB1*0201 positive samples with additional DRB1*04 subtyping in DQB1*0302 carriers. The combination of the following markers gave a relative risk of 28.9 (95% confidence interval: 15.9-52.7, p = 10(-6): DQB1*0201/0302-DQA1*0301,0501-b (b not equal to DRB1* 0403), DQB1*0302/x-DRB1*0401,0402 (not equal to DQB1*0201, 0301,0602,0603), DQB1*0301/0302-DRB1*0401,0404, DQB1*0304/s (s = any DQB1 alleles), DQB1*0201/y-DQA1*0501/a (y not equal to DQB1*0301,0302,0602, 0603,0604, a not equal to DQA1*0201). The diagnostic sensitivity, specificity and positive predictive values for this marker combination were 79.2%, 88.7%, and 1.1%, respectively. CONCLUSIONS: Using HLA DRB1-DQA1-DQB1 markers predictive genetic screening for type 1 diabetes is feasible in the Hungarian population with high diagnostic sensitivity and specificity. At present, such a screening for individuals at risk for type 1 diabetes in the general population is recommended only as part of prospective studies on the natural history or prevention of disease. To increase the positive predictive value of the model, pancreas beta-cell autoantibodies need to be measured and followed in the high-risk cohort.     

河北省糖尿病流行病学研究

为探索河北省城乡非胰岛素依赖型糖尿病（ＮＩＤＤＭ）流行趋势和患病的危险因素，对６个城乡进行了抽样调查和分析。结果表明，抽样人口ＮＩＤＤＭ患病率为２．７９％，标化率２．３４％；城市人口患病率３．０３％，农村为２．５６％；人均收入高的城乡，ＮＩＤＤＭ患病率亦高。高龄、肥胖、阳性家族史者是ＮＩＤＤＭ的高危人群。经多因素分析，人均收入高及饮食开支大、家族史、肥胖及肉、蛋、油、奶类的大量摄入是ＮＩＤＤＭ高发的危险因素，玉米等粗粮摄入、体育锻练和职业体力劳动是保护因素。提示营养过剩、运动缺乏、教育不足是ＮＩＤＤＭ发病的主要原因。     

Low yield of population-based screening for Type 2 diabetes in the Netherlands: the ADDITION Netherlands study

BACKGROUND: About 10 years ago, it was estimated that half of all people with diabetes were unrecognized. Since then, according to the national guidelines, case finding for diabetes in general practice has become common in the Netherlands, resulting in a substantial increase of the prevalence of known diabetes. Nevertheless, the need for population-based screening is advocated, especially by the national federation of diabetes patients. OBJECTIVE: To evaluate the efficiency of population-based screening for Type 2 diabetes. METHODS: From 2002 to 2004, we performed a four-step screening procedure [questionnaire, random glucose measurement, fasting glucose measurement and oral glucose tolerance test (OGTT)] and a three-step procedure (without random glucose measurement) in 79 general practices in the southwestern region of the Netherlands. RESULTS: A total of 56 978 non-diabetic subjects, aged 50-70 years, were asked to complete the questionnaire. Those with a score above threshold underwent further glucose testing. Eventually, 586 participants (1.0%) were diagnosed with Type 2 diabetes (in four-step procedure 285 subjects and in three-step procedure 301). Impaired glucose regulation was assessed in 1011 participants (1.8%). Dropout rate in the screening programme among participants who should undergo an OGTT was 23.4%. The risk score was higher if glucose metabolism was more disturbed. CONCLUSION: In the Netherlands, the yield of population-based screening is low. The dropout among high-risk individuals was high. Given the decreasing prevalence of undiagnosed diabetes and the possibility of opportunistic screening on a continuous basis, opportunistic screening for diabetes might be more appropriate than population-based screening. Further research on this topic is needed.     

Community screening for cardiovascular risk factors and levels of treatment in a rural Māori cohort

Objectives : To document levels of cardiovascular disease (CVD), diagnosed and undiagnosed risk factors and clinical management of CVD risk in rural Māori. Methods : Participants (aged 20–64 years), of Māori descent and self‐report, were randomly sampled to be representative of age and gender profiles of the community. Screening clinics included health questionnaires, fasting blood samples, blood pressure and anthropometric measures. Data were obtained from participants’ primary care physicians regarding prior diagnoses and current clinical management. New Zealand Cardiovascular Guidelines were used to identify new diagnoses at screening and Bestpractice© electronic‐decision support software used to estimate 5‐year CVD risk. Results : Mean age of participants (n=252) was 45.7±0.7, 8% reported a history of cardiac disease, 43% were current smokers, 22% had a healthy BMI, 30% were overweight and 48% obese. Hypertension was previously diagnosed in 25%; an additional 22% were hypertensive at screening. Dyslipidaemia was previously diagnosed in 14% and an additional 43% were dyslipidaemic at screening. Type‐2 diabetes was previously diagnosed in 11%. Glycaemic control was achieved in only 21% of those with type‐2 diabetes. Blood pressure and cholesterol were above recommended targets in more than half of those with diagnosed CVD risk factors. Conclusions : High levels of diagnosed and undiagnosed CVD risk factors, especially hypertension, dyslipidaemia and diabetes were identified in this rural Māori community. Implications : There is a need for opportunistic screening and intensified management of CVD risk factors in this indigenous population group.     

Identifying people at risk for undiagnosed type 2 diabetes using the GP's electronic medical record

BACKGROUND: Screening for type 2 diabetes is recommended in at-risk patients. The GP's electronic medical record (EMR) might be an attractive tool for identifying them. OBJECTIVE: To assess the value of the GP's EMR in identifying patients at risk for undiagnosed type 2 diabetes and the feasibility to use this information in usual care to initiate screening. METHODS: In 11 Dutch general practices (25 GPs), we performed an EMR-derived risk assessment in all patients aged > or =45 and < or =75 years, without known diabetes, identifying those at risk according to the American Diabetes Association recommendations. Patients with an EMR-derived risk or risk after additional risk assessment during regular consultation were invited for capillary fasting plasma glucose (FPG) measurement. RESULTS: Of 13 581 patients, 3858 (28%) had an EMR-based risk (hypertension, cardiovascular disease, lipid metabolism disorders and/or obesity). Additional risk assessment in those without an EMR-based risk showed that in 51%, greater than one risk factor was present, mainly family history (51.2%) and obesity (59%). Ninety per cent returned for the FPG measurement. In both groups, we found patients with an FPG exceeding the cut point for diabetes (5.9% versus 4.1%). CONCLUSIONS: With additional risk assessment during consultation, the GP's EMR was valuable in identifying patients at risk for undiagnosed type 2 diabetes. It was feasible to use this information to initiate screening. At-risk patients were willing to take part in screening. Better registration of family history and obesity will improve the EMR as a tool for identifying at-risk patients in opportunistic screening in general practice.