Background information on screening as an intervention

The following table gives an overview of differences between screening practices. Details are described below.

Table 1: Overview and separation of screening strategies

History of Screening

The first routine investigations in healthy people were done around 1860 concurrently in the UK and the USA. At that time the main purpose was to gain new scientific insights into diseases and their prevention. Routine investigations were rapidly accepted in the USA because of the endorsement of insurance companies, who wanted to minimise the health risk profiles of their members, employers who wanted to ensure a healthy workforce and increase productivity, and because of medical scientists, who wanted to continue their pioneering task even if neither the health-related, nor the financial benefit of such routine investigations was clear at the beginning. In Europe, the need for quality assured and informed screening programmes has become more accepted since 1960. Current and future challenges to screening involve the weakened traditional authority of medical science, the changing risk awareness of the population, the advancement of genetic research, the decentralisation of healthcare and the growing financial burden of healthcare costs. {1}

Definition of Screening

The definition of screening and what people really mean when they use the term screening varies widely between professional groups and with time and local conditions. The primary objective of medical screening is to identify a disease or condition in its preclinical and therefore potentially curable stage in apparently healthy people or people believing themselves to be healthy.

For identification of a disease or condition, individual screening tests or a quality assured and evidence based screening programme, which includes all relevant interventions to reduce risk, can be applied. Additionally, every person in the entire population, or a target subgroup of the population with a high prevalence of risk factors for a certain disease or condition, can be included for screening. Furthermore, screening can be implemented in the inpatient or outpatient sector and executed by different experts. On the basis of the screening results people may be offered information, further assessments and/or appropriate therapy. {2, 3}

Screening does not apply to investigations, performed at a time when signs and symptoms of a disease have already occurred. However, there are some tests and investigations, which are carried out in healthy people and fulfil some criteria of screening programmes, but are not defined as having screening as their primary intention, for example occupational investigations at a workplace, preliminary investigations before operation, epidemiological surveys, lifestyle and fitness assessments or investigations for secondary disease. {1}

Requirements for screening

Before starting to plan and implement screening practices for a condition or disease, it is important to check if the criteria for viability, effectiveness and appropriateness are fulfilled. In 1968, the World Health Organization published principles and practices of screening for disease and listed some basic criteria that should ideally be fulfilled: {4}

1. The condition or disease should be an important health problem.
2. An accepted and effective treatment should be available.
3. Facilities for diagnosis and treatment should be available.
4. The condition or disease should have a recognisable latent or early symptomatic stage.
5. There should be a suitable test or examination.
6. The test should be acceptable to the population.
7. The natural history of the condition, including development from latent to declared disease, should be adequately understood.
8. There should be an agreed policy on whom to treat as patients.
9. The screening cost should be economically balanced in relation to total medical expenditures.
10. Case-finding should be a continuing process and not a "once and for all" project.

Additionally, detailed criteria, developed by the UK National Screening Committee, are available online http://www.screening.nhs.uk/criteria. {2}

Implementation of a screening programme

How a screening programme should be or is implemented depends on healthcare systems, strategies, medical services offered and financing of the screening programme. Essential elements that influence improvements in the health of a population as a result of implementing a screening programme are listed below. {1, 5}

• Coordination and project management of the screening strategy.
• Setting up objectives (in general and in detail) and policy.
• System development and information management.
• Constituting operative methods.
• Quality assurance.
• Analysis and assessment of evidence; assigning new research.
• Screening equipment (equipment needed; equipment default set up; safety, compliance and quality assurance on machines; equipment review and replacement; transport of equipment; storage; consumables and other items needed; cleaning; packing up instructions).
• Accommodation requirements (clinic rooms, screening office, etc.).
• Organisation of public relations (leaflets, website, poster, etc.).
• Identification of relevant people.
• Invitation of relevant people.
• Information and consultation of participants.
• Staff requirements (for example: project management team, [clinical] leader, clinicians, consultants, clinical skills trainer, screening staff, screening technicians, nurse practitioners, coordinator, clerical officer for administration, medical physicist, IT lead, other organisations, etc.) and responsibilities.
• Workforce education and training.
• Realisation of diagnostic investigations and screening tests.
• Statistical evaluation of the realisation of screening.
• Carrying out necessary interventions/treatment after screening.
• Documentation (screening process, test results, appointments, following treatment, use of data, administration, consent declined or withdrawn, storage and transfer of person-identifiable data, incident reporting, etc.).

Screening Practices

The following types of screening can be undertaken.

1. Population-based systematic screening

a) Population based approaches that attempt to systematically screen every person in the entire population.

b) Selective screening approaches that target subgroups of the population with a high prevalence of risk factors for a certain disease or condition.

The process of population-based systematic screening can be divided into the following stages {5}:

• identification of the relevant cohort  
• invitation of eligible people  
• informing eligible people about screening before the decision to participate or not is taken
• testing the people entering the screening programme (the programme ends at this point if the test results are within normal limits)  
• surveillance and forward planning if a risk for the disease exists but no immediate treatment is needed  
• diagnosis of the disease and further actions  
• treatment or intervention, taking into account valid guidelines  
• monitoring outcomes

1. Various opportunistic screening practices/usual care

(a)    The physician screens individuals occasionally during routine healthcare examinations (selective screening for individuals). The patient is presumed well or is not complaining of the disease for which screening is offered. The physician has no special reasons to suspect illness but complies with an accepted standard of good diagnostic practice.

(b)   The physician examines only those patients who consult him or her because of some complaints.

For various opportunistic screening practices for AAA no specified screening process is defined. In most cases, it is done in the primary care setting as an add-on investigation to other primary prevention investigations, or an AAA may occasionally be detected when a different indication is primarily being examined by the practitioner.

Screening in practice

Population-based systematic screening and various opportunistic screening practices can consist of {1, 6}

(a) individual medical investigations, including screening tests and interventions which altogether result in a screening programme or

(b) quality assured and evidence based screening programmes, which include all relevant interventions to reduce risk.

The implementation, realisation and financing of screening vary between the different screening practices and healthcare systems {1}:

• Governmental financing and offering of quality assured and evidence based national screening programmes (e.g. UK).
• Governmental reimbursement of costs for recommended screening interventions by independent or national providers (e.g. Australia).
• Only some health insurance agencies offer recommended screening from specified providers. Patients must decide whether they can afford it (e.g. USA).

Additional Benefits of AAA-screening

Detection of AAA by any screening procedure may act not only as a decision tool for planning elective surgery but also as a tool to intensify and supervise lifestyle modifications for the patient (i.e. smoking cessation, optimising antihypertensive pharmacotherapy,…).

Limitations of AAA-screening

The implementation of screening practices has the potential to save lives or improve quality of life because of early diagnosis of serious diseases or conditions, but it cannot guarantee protection. In any screening practice, there is a potential for harms and adverse events for patients, e.g. during the screening test, during diagnosis or during treatment. There is, for example, the potential for false positive results in individual screening tests, which may be a considerable psycho-social burden for those concerned. Additionally, false positive results can result in unnecessary investigation and treatment. On the other hand, false negative results delay the detection and final diagnosis of a disease. During the screening test, patients could be exposed to radiation or chemicals or undergo discomfort, stress or anxiety, all of which could lead to adverse effects. Therefore it is essential to establish whether, in practice, screening a healthy (risk) population leads to an improvement of relevant outcomes. {2, 7}

For abdominal aortic aneurysm screening different practices exist (population-based systematic and various opportunistic screening practices). In most countries no systematic and nationwide screening programme is implemented. Decisions about screening are made individually by primary care physicians. In addition, several cardiovascular societies have published recommendations concerning who should be screened and under which conditions. All of the recommendations require clinicians to individualise care and recommendations depending on the patient's risk and likelihood of benefit.

The following table gives an overview of the AAA screening strategies of various countries {8}.

Table 2: Overview of country-specific AAA screening practices

Published guidelines on AAA screening attempt to close the gap between the best available evidence and what physicians do in their practices. In their systematic review of guidelines on abdominal aortic aneurysm screening, Ferket et al. (2012) {11} identified seven relevant guidelines and the quality of development of each guideline included was determined by the Appraisal of Guidelines Research and Evaluation (AGREE) instrument. The AGREE instrument is a validated tool to evaluate the process of practice guideline development and the quality of reporting. {12}

Table 3: Guidelines on AAA screening (Ferket et al. 2012) {11}

Details of guidelines on AAA screening included in the systematic review of Ferket et al. {11} are reported below.

Table 4: Details of Guidelines on AAA screening (Ferket et al. 2012) {11}

The US Preventive Services Task Force (USPSTF) {7} recommends one-time screening for abdominal AAA by ultrasonography in all men aged 65 to 75 years, who have smoked at least 100 cigarettes in their lifetime. This recommendation is based on the evidence that surgical repair of large AAAs (5.5 cm or more) on the basis of screening leads to decreased AAA-specific mortality and therefore outweighs screening-associated harms in this population group. The USPSTF states that the harms of AAA-screening in men aged 65 to 75 years, who have never smoked, in men aged more than 75 years and in women in general balance or outweigh the benefits. Men aged more than 75 years are at higher risk for AAAs, but the increased presence of comorbidities and limited life expectancy decreases the likelihood that they will benefit from screening.

Summarizing the systematic review of guidelines from Ferket et al. (2012) {11} shows that most of the seven included guidelines contain recommendations that favour one-time AAA screening for men aged 65 years and older. Every guideline reasoned that abdominal ultrasonography is the primary screening test. Only one guideline group (ACC) recommended physical examination as a useful screening tool in addition to ultrasonography. The guidelines did not agree on whether a smoking history should be present or not. Additionally, four guidelines (three of them had low AGREE scores) contained disparate recommendations on screening women and middle-aged men at elevated risk, whereas guidelines with higher AGREE scores did not. The criterion for elective surgical repair in elderly men for an abdominal aortic diameter of 5.5 cm was unanimously used but there was no consensus on the management of smaller AAAs.

Most of the guidelines give recommendations for surveillance of patients with aneurysms smaller than 5.5 cm in diameter but these recommendations vary in the intensity of follow up and the cut-off points of the aorta diameter. For example, some guidelines recommend that an annual abdominal ultrasound is acceptable if the AAA is 3.0 to 4.4 cm. Others recommend that if the AAA diameter is between 4.0 and 5.4 cm, surveillance should be done every 6 to 12 months. If the AAA is <3.0 cm, some guidelines recommend no follow-up surveillance before 3 to 5 years. Other guidelines say that aneurysms 3.0 to 3.9 cm in diameter should be surveyed every 2 to 3 years, and those 4.0 to 5.4 cm in diameter should be assessed every 6 months. {11}

The typical expansion rate of AAA is around 0.3-0.4 cm per year, on average. As the expansion rate of AAAs is positively correlated to size, surveillance intervals should depend on size. As a patient's health status may change during the surveillance period, continued AAA surveillance should occur only if the patient remains a good surgical candidate and has a reasonable life expectancy. If the first-time ultrasonography screening for AAA revealed normal aortic diameter, there is no need for re-screening, as negative results appear to virtually exclude the risk for future AAA rupture. {9}

In conclusion, even if the officially accepted cut-off point for elective surgery has been set to an aneurysm size of 5-5.5 cm, the final decision about going ahead with a surgical procedure must be considered individually taking into account the option of endovascular treatment, age, comorbidities and other factors.

Question refers partly to RC-CUR10, RC-EFF24.

Ultrasonography as gold standard

Ultrasonography has been established as the gold standard technical device for screening for AAA. Different investigations show that ultrasonography is a valid diagnostic technique for the detection of AAA with both sensitivity and specificity of nearly 100%. The test is non-invasive, relatively inexpensive and fast, and patients are not exposed to ionizing radiation. Additionally, this test is highly acceptable to patients. {13-17}

More than 80% of all AAAs are detected occasionally or through ultrasonography screening {18}. If an AAA is suspected or if an AAA is detected through ultrasonography screening, further medical investigations are carried out to verify the diagnosis and define treatment, for example, computed tomography (CT) or magnetic resonance imaging (MRI).

For detection of AAAs, other diagnostic technologies, besides ultrasonography, are also used. For example abdominal palpation, CT or MRI (see result card TEC 8, {8, 13, 19}) but ultrasonography is the detection method of choice for AAA screening {13-17}.

For ultrasonography various image-guided methods are available, such as the colour-coded duplex sonography that is most often used. In brief, colour-coded duplex sonography is an ultrasound-based imaging method, using high-frequency sound waves to reflect the structure of inner organs or blood vessels. A computer receives these reflected waves and uses them to create a picture, visualizing possible pathology. Most devices can additionally study the relative velocity of the blood flow or whether the blood flow is moving towards or away from the transducer. Such measurements are based on the Doppler effect (which, within certain limits allows the accurate assessment of the direction and velocity of the blood flow by calculating the frequency shift of the flow-wave and visualizing it in colour). However, currently no standards for the display of colour-coded duplex sonographic images are available. Some laboratories use red to display arterial vessels and blue to display venous vessels; others use colours to indicate the direction of the flow either towards the transducer or away from it. To interpret the results, knowledge of the physiology and pathophysiology of blood flow in the body is therefore important. {20}

Throughout Europe, Siemens Healthcare and GE Healthcare are currently the leaders in the distribution of colour-coded duplex-sonographic technical devices. {21} Figure 1 shows an example of such a device, including the monitor and keyboard.

Figure 1: Colour-coded duplex-sonographic technical device

Figure 2 shows the duplex sonographic documentation of the transverse diameter of an infrarenal abdominal aortic aneurysm. The black area within the arrows represents the lumen of the expanded aorta.

Figure 2: Duplex sonographic documentation of an AAA

Figure 3 illustrates the transverse diameter of an infrarenal abdominal aortic aneurysm in colour-coded mode. The red colour represents arterial blood flow.

Figure 3: Transverse diameter of an AAA

Question refers partly to RC-EFF24, RC-EFF25.

• Handsearch

Screening for abdominal aortic aneurysm is used to identify this disease or condition in its preclinical and therefore potentially curable stage in apparently healthy people or people believing to be healthy. {1}

Question refers to RC-CUR1, RC-CUR8, RC-TEC1, RC-TEC2, RC-TEC3 and RC-EFF32.

Users of screening

AAA screening is usually done by physicians (predominantly general practitioners or medical doctors specialising in internal medicine; opportunistic screening practices) or medical technical assistants (population-based systematic screening). {22}

Necessary training

Usually, residents can be trained to perform ultrasound assessments adequately to identify high risk AAA patients. For the technical aspect of AAA screening, the grade and level of training seems to be more important than the type of medical discipline. {23}

Specificity, sensitivity and reproducibility

Variation in intraobserver repeatability and reproducibility of AAA screening by colour-coded duplex-sonography has been identified among studies, which may be in part related to the fact, that investigations were performed by investigators from different medical disciplines of varying grades and levels of training {24}. As poor reproducibility (above the level of 5 mm [which is accepted by the UK and USA AAA screening programmes]) may have negative impact on screening and surveillance, training and quality assurance are important factors of AAA screening.

Question refers partly to RC-CUR11, RC-CUR25 and RC-CUR12.

As mentioned in TEC 1 the screening process consists of different stages depending on whether a population-based systematic screening programme or various opportunistic screening practices are implemented.

Population-based systematic screening programme

For the National Health Services (NHS) AAA Screening Programme {5} in England standard operating procedures (SOP) are designed to inform and assist screening leads, strategic health authorities and other key stakeholders to establish and implement a new AAA population-based screening programme. The necessary elements of a screening programme, the screening pathway and quality assurance processes, and requirements for programmes are described. These SOPs state that the minimum population for selection of a population-based screening programme is 800,000 patients with detected AAA, which could be treated in a suitable medical centre. In the NHS AAA Screening Programme men are automatically invited by letter in the year they turn 65 years and men who are older than 65 years, and who have not previously been screened or treated for an abdominal aortic aneurysm, can opt in through self-referral direct to the screening programme (see CUR). The invitation comes from the local screening office and not from the general practitioner. {5}

In Sweden the population-based screening programme screens a defined healthy population (with defining a risk profile/an eligible population) by an invitation to a screening programme. Eligible people are invited by e-mail by the Register of Total Population managed by Statistic Sweden including age and gender. {8}

In the USA patients are eligible for population-based AAA screening if they have a family history of AAA, and/or if they are a man, age 65 to 75 years who has smoked at least 100 cigarettes in his lifetime and has never had an AAA ultrasound screening paid for by Medicare. {9}

Various opportunistic screening practices

For various opportunistic screening practices no specified population is defined for which AAA screening should be used. Usually, persons at risk are most likely adverted by assignments by their general practitioners.

Question refers partly to RC-CUR7, RC-TEC1, RC-TEC2, RC-TEC3, RC-SAF2 and RC-ORG11.



Ultrasonic energy was first used for medical purposes (for neurological problems) in the late 1940s. The first compound contact B-mode scanner (the patient sat in a water-filled barrel with the sensor circulating around) was developed 20 years later and the first commercial hand-held transducer was released around 1965. Since then, concurrently in various countries, sonography became used more and more frequently by a range of medical disciplines. Around 1960 the Doppler effect principle was applied for the first time for cardiovascular diagnostics. Colour-coded duplex sonographic devices were launched only after 1980, when computer technology was applied to enhance sonographic pictures. Since then the image information on ultrasound machines has improved rapidly. {25, 26}

Question overlaps partly with RC-CUR17 and RC-ETH1.

AAA may be diagnosed by a variety of methods, including physical examination (presenting as a palpable pulsatile tumour), ultrasonography, CT, MRI, angiography or radiography. CT images are three-dimensional images of the inside of the body that are generated from a large series of two-dimensional X-ray images, which are taken around a rotational axis and are especially useful for preoperative clarification of detailed anatomy and endovascular repair eligibilities. MRI, which uses the property of nuclear magnetic resonance to image nuclei of atoms inside the body and angiography, which visualises the inside of blood vessels by injecting a contrast agent into the blood vessel and imaging it using X-ray based techniques, are both more expensive than the other methods. AAA imaging by radiography is only possible in case of calcification of the aneurysm wall, which occurs in less than 50% of all AAAs {27}.

For AAA screening and determination of AAA-diameter, ultrasonography has been established as the gold standard. This technique is non-invasive, sensitive, portable and inexpensive. However, applicability may be reduced in obese people. Even if long term biological effects of diagnostic ultrasound exposure cannot be determined today {28}, most medical doctors feel that for the patient the benefits of correctly performed ultrasound outweigh the risks {29}. Nevertheless, investigations should be restricted to clearly indicated diagnostic questions. Scanning time should be held as short as possible and power should be set as low as possible, following the ALARA (As Low As Reasonably Achievable) principle {30}.

It has been proposed that population-based systematic screening programmes for AAA by ultrasonography offer a clear benefit over harm and are ethically justified as long as people are given adequate information {31}.

Ultrasonography is applicable for a wide spectrum of medical diagnostic assessments, including imaging of the heart muscle and the cardiac valves, prenatal diagnostics and gastroenterological investigations. With respect to the vascular system, colour-coded duplex sonography is applied, not only to assess potential vascular dilation, stenosis or occlusions of the carotid artery, the abdominal aortic artery and the peripheral arteries of the upper and lower extremities, but also enables detection of venous diseases, including varicosities and deep venous thrombosis. Ultrasound waves also may be used for therapeutic reasons. {32}

Question refers partly to RC-SAF4, RC-SAF7 and RC-EFF18.

Along the whole screening process, mentioned in result card TEC 1, different healthcare settings are affected.

Population-based systematic screening programme

In a population-based systematic screening programme, the testing of the people entering the programme can be undertaken in inpatient and outpatient settings. For example in the UK, ultrasound scanning for AAA is undertaken within community healthcare facilities. These are dedicated screening clinics, for example community clinics, community hospitals, mobile units or primary care facilities. Additionally, the patients themselves and general practitioners should be informed about the results of the test and whether or not referral to a vascular consultant in a hospital outpatient department or vascular centre is required (for surveillance, diagnosis and/or monitoring). The surgical treatment for AAA is undertaken in a vascular unit. {5}

In Sweden, screening is performed in imaging departments at hospitals or in separate units that specialise in ultrasonography. {8}

Various opportunistic screening practices

For various opportunistic screening practices for AAA no specified place or context is defined. Various opportunistic screening practices are usually done in the primary care setting, in most cases as an add-on investigation to other primary prevention investigations. In case of borderline positive screening results patients are usually referred to specialised units, such as a department for internal medicine with a major focus on cardiovascular diseases.

Question refers partly to RC-ORG1, RC-ORG5, RC-ORG6, RC-ORG16 and RC-ORG17.



By definition, the size of the abdominal aorta is considered normal if it does not exceed 2.5 cm as measured by ultrasound. Enlargement of abdominal aortic diameter to 2.5 cm or more is diagnosed as “Ectasia” (2.5 cm–3 cm) and to more than 3 cm as “Aneurysm” (13). Regarding the reliability and reproducibility of inner to inner diameter (excluding the arterial wall; ITI) versus outer to outer diameter (including the arterial wall; OTO) ultrasound measurement of AAA diameter, it is assumed, that the ITI wall method is more reproducible. {22}

To assess the rupture risk of an AAA, however, more reliable parameters than diameter are peak wall stress and peak wall rupture risk. {33}

The ultrasound device must be available in the institution or hospital where the test is carried out. In most case, packages with computers and software included are offered and installed by the companies. A printer is necessary, if printed pictures and reports are warranted. As already mentioned, the technique is applicable for a wide spectrum of medical diagnostic assessments, whereby one and the same device may be used by the different medical disciplines. Depending on the region of interest, investigators have to choose between transducers of different tissue-penetration depths. {34}

In UK, the screening equipment is purchased centrally and a technical equipment specification has been developed. The technical equipment consists of portable ultrasound machines, producing good quality black and white images, with digital recording devices from where data can easily be downloaded. The machines should be able to store and transfer data digitally. Additionally, an examination couch, wipes, a transducer and mobile computer media and devices are necessary. {5}

Question refers partly to RC-TEC11, RC-ECO1, RC-ECO2, RC-ORG7 and RC-ORG8.

Examinations can be performed at the bedside. As the investigation has to be performed with the patient in a supine position, application of the technology requires an examination couch, if possible, adjustable for height. To use the technology the only necessary disposable item is a water-based conducting gel to facilitate the transmission of the sound waves. As the technology is non-invasive, neither needles, nor bandages or medicines are necessary. The use of paper towels may be helpful to remove conducting gel from the skin after the investigation. {34}

Question refers partly to RC-TEC10, RC-ECO1, RC-ECO2 and RC-ORG4.

Question refers to RC-ORG10.

Question refers to RC-ORG3, RC-ORG4 and RC-SAF9.

Question refers to RC-SAF9, RC-ORG3 and RC-ORG4.