A controlled trial of multiphasic screening in middle-age: results of the South-East London Screening Study*

The South-East London Screening Study Group

Abstract

South-East London Screening Study Group (Department of Community Medicine, St Thomas's Hospital and Medical School, London SE1 1EH, England). A controlled trial of multiphasic screening in middle-age: results of the South-East London Screening Study. International Journal of Epidemiology 1977;6:357–63. The results of a controlled trial of multiphasic screening in general practice are presented. In 1967, 7229 individuals aged between 40 and 64 years were randomly allocated into either a Screening or Control group. The Screening group were invited to attend two screening sessions held about two years apart, while the Control group continued to receive conventional medical care. Both groups were then invited to undergo a health survey in 1972–73 which revealed no significant differences in morbidity between the two groups. Careful follow-up permitted detailed Screening-Control comparisons of various outcome measures—consultation and hospital admission rates, certified sickness absence from work, and mortality. Nine years after the initial screening, no significant differences were found between the two groups in any of the outcome measures. It is estimated that a similar screening programme for the entire middle-aged UK population would cost £142 million at 1976 prices.

Introduction

In 1967, a long-term controlled trial of multiphasic screening for diseases of middle-age was embarked upon jointly by two group general practices in South London and the Department of Community Medicine at St Thomas's Hospital. The purpose of the study was to assess the value, if any, of introducing a general practice based screening service for 40- to 64-year-olds as an extension of the existing National Health Service.

This paper reports the results of the study, various aspects of which have been previously described.1–5

Methods

The study was designed as a controlled trial (Figure 1Go) in which two large group practices in South London participated. Using age-sex practice registers, all persons aged 40–64 years in 1967 were identified and randomly allocated by family within general practitioner list into two equal groups designated Screening and Control (Table 1Go). The Screening group was then invited by personal letter from their general practitioner to be screened. Each screening clinic operated an appointment system and was held in the evenings in local infant welfare clinics. They were staffed by nurses and specially trained local housewives who were aided and supervised by a doctor. At the clinics, a health questionnaire was administered and a series of clinical tests performed (Table 2Go). The questions and tests were selected, after extensive discussion and consultation, according to the twin criteria of diagnostic reliability and therapeutic significance.



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Figure 1 Screening study—overall plan. NB. N is the total number present at a particular point in time INVITED for screening. Changes reflect deaths, departures and administrative difficulties

 

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Table 1 Demographic details of the screening and control groups*
 

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Table 2 Test used in multiphasic screening procedure
 
The initial screening was carried out in 1967–68. Two years later, the Screening group was invited by letter to attend a second screening clinic, where a similar battery of tests was performed. These two screening sessions constituted the ‘treatment’ under assessment in the controlled trial.

At the first screening in 1967–68, the general practitioner conducted a physical examination on each individual. All information gathered at both screening sessions was passed to the general practitioners who decided what further investigations, diagnoses and treatments would be appropriate.

From the first day of screening, information was collected at six-monthly intervals on all consultations with the general practitioner, hospital admissions and periods of certified sickness absence. In addition, all deaths and departures from the study were carefully recorded in both screening and control populations.

It soon became clear that the migration rate from the study area was high—20 per cent of the study population over the first five years. In order that an additional assessment of outcome could be made before the residual population became unrepresentative of the original, a further method of evaluation was employed. This took the form of a survey of both the Screening and Control groups two years after the second screening. Essentially, this survey was a repeat of the previous screening procedures so that direct comparisons of clinical measurements (for example, blood pressure levels) in the two groups could be made.

Results

For the purpose of this report, all the results are presented for the two practices combined unless otherwise stated.

Response to screening
Of the 3297 individuals invited to the first screening, 2420 (73.4 per cent) took up the invitation. At the second screening, of the 2677 invited individuals, 1775 (65.5 per cent) attended. For the survey, efforts were made to encourage those who refused the initial invitation to attend the clinic or at least give some health information at home. Consequently, the response rate was higher than at the two screening sessions. Detailed response rates have been reported previously.4

Yield and management of disease at screening
An average of 2.3 diseases per person screened was found at the initial screening. Fifty-three per cent of this morbidity was not previously known to the general practitioners. Ninety-five per cent of the unknown abnormalities were of a minor nature, being neither disabling nor life-threatening. Of the serious diseases discovered by screening 56.3 per cent were already known. For the majority of abnormalities revealed by screening, with the exceptions of anaemia and high blood pressure, little new therapeutic intervention was introduced, although advice on stopping smoking and weight reduction was given to all for whom it was appropriate.

At the screening two years later, the yield of disease was lower than at the first screening. For example, whereas 2.1 per cent (50 persons) were newly diagnosed as hypertensive following the first screening, only 0.5 per cent (9 persons) were newly diagnosed as such after the second.4

Outcome measures of screening
The Screening and Control groups have been compared with respect to the various outcome measures (findings at the survey, general practice consultation rates, hospital admissions, sickness absence and mortality rates) over the first nine years since the start of the study.

(a) Comparisons at survey
The health survey of both Screening and Control groups revealed no significant differences between them in either the prevalence of symptoms or level of function. Prevalence figures for some of the measurements are illustrated in Table 3Go. A very thorough examination of all the outcome variables was undertaken using a multi-factor analysis6 taking into account age, sex, social class, smoking habit, blood pressure, blood sugar, serum cholesterol and general practice group. No significant differences could be demonstrated between the Screening and Control groups.


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Table 3 Some measures of morbidity—Screening versus Control groups at the concluding Health Survey in 1972/73 five years after the initial screening
 
(b) General practice consultation rates
The Screening population appeared to have a higher consultation rate than the Control group (Table 4Go). However, this was not statistically significant (t = 1.29).


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Table 4 Average annual GP consultation rates for subjects in the study for more than one year; Control versus Screening totals: C = 2730; S = 2844
 
(c) Hospital admissions
Table 5Go shows the results from the hospital admission data for the Screened and Control populations. It also illustrates the risk of at least one admission both overall and within specific disease groupings. None of the observed differences are larger than could easily have occurred by chance. In addition, considering all admissions there appear to have been more in the Screening group, but again the differences are not statistically significant.


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Table 5 Hospital admissions Control versus Screening 1967–1976
 
(d) Certified sickness
There were no significant differences in certified sickness absence between Screening and Control populations. There were large differences between men and women, since many of the latter were not entitled to sickness certification. The figures for men showed that in both the Control and Screening groups overall 5.5 per cent of their time was lost through certified sickness absence. The proportion of time lost tended to rise up to the age of 60, thereafter it decreased.

(e) Mortality
There were no statistically significant differences in the mortality experience of the Screening and Control populations during the first eight years of the study. More detailed analysis using survival curves similarly failed to reveal significant differences. As an example, the survival curve for the sub-group which has the highest mortality, namely the older men, is shown in Figure 2Go.



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Figure 2 Survival curves of men over 60 years in 1967/8. Screening versus controls

 
Table 6Go shows the death rates by cause taking into consideration the number of man-years at risk. No significant differences between the two groups were found for any cause of death, though a marked sex difference was apparent.


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Table 6 Death rates by cause Control versus Screening 1967–1975
 
Costs

The crude average cost of screening (followed by one general practitioner consultation where necessary) was estimated retrospectively; this cost excludes adjustments for alternative uses of capital. At 1967 prices the average figure was £6045 per 1000 persons screened. At 1976 prices, it is estimated that the cost of screening would be £12.27 (with a range from £15.39 to £9.35). This is a relatively low figure, being approximately a fifth of that charged by private screening organisations in the UK in 1976. Calculations suggest that once the screening clinics were operational, screening one extra person would cost still less—£4.35 at 1976 prices—because most of the initial cost reflects expenditure on manpower and equipment required to establish the service.

Discussion

Regular health ‘check-ups’ by doctors or screening clinics have become an accepted and valued part of the health services of many developed countries. The rationale of such examinations is two-fold—not only might they detect the so-called ‘ice-berg’ of unrecognised disease enabling the institution of earlier and presumably more effective treatment, but they might also identify potentially reversible risk factors such as high blood pressure.

The results presented in this paper must cast considerable doubt on many assumptions about the value of multiphasic screening in middle age. None of the outcome measures of mortality, morbidity or health service usage has been shown to be improved by screening. The screening service itself, however, appeared to have been generally well received by the population to which it was offered and this was reflected by the repeated response rates of over 70 per cent of those invited. The costs incurred by the clinics would amount to more than £142 million (at 1976 prices) if a similar programme were offered to the entire middle-aged UK population—assuming that the formidable administrative problems could be overcome.

The only other large-scale controlled trial of multiphasic screening to have published results is that of the commercially based Kaiser Permanente Group in California.7 These workers failed to demonstrate any statistically significant differences in the overall death rates when the treatment and control groups were compared seven years after the start of the study. Certain specific cases of mortality in particular age groups did appear to show significantly improved rates in the screening group, but only three of the 60 statistical tests undertaken were reported as showing significant results, two in favour of the screening and one against it. This is approximately the same outcome that one would expect purely by chance.

Considerable confusion has arisen in recent years over the use of the term ‘screening’, which usually implies that the doctor has approached the patient in the first instance, rather than vice-versa. The term ‘case-finding’ has been applied to those tests undertaken by medical workers on patients who are already consulting for unrelated symptoms.8 In the first five years of this study, 93 per cent of all patients on the lists within this age group had attended their doctor at least once.4 Case-finding, rather than screening, may therefore offer a more attractive (and perhaps more effective) approach to early disease detection and prevention in the future.

Finally, the paucity of real medical benefit derived from this enormous outlay of effort and resources may disappoint screening enthusiasts. However, as Wilson and Jungner,9 Sackett and Holland8 and others have emphasised, the doctor-initiated search for unrecognised disease in healthy individuals carries with it a number of ethical obligations. If disease is found, an effective and acceptable treatment should be available. Any form of screening, including multiphasic, must therefore be judged on the basis of its demonstrable health benefits. Since these controlled trial results have failed to demonstrate any beneficial effect on either mortality or morbidity, we believe that the use of general practice based multiphasic screening in the middle aged can no longer be advocated on scientific, ethical or economic grounds as a desirable public health measure.

Acknowledgments

The South-East London Screening Study has involved the participation of many individuals, only some of whom can be acknowledged by name. We would like to thank Drs U Kroll, IN Manser, NH Barley, HB Raeburn, GSW Sharpe, JD Paulett, TA Williamson, JMG Wilson and K Randall; Mr J Dunlop, Ms Rachel Fielden, Mr Robin Milne, Miss Deborah Brown, Miss Nalini Shah, Miss Debbie Reynolds and Miss Juliet Chadwick. The study was supported in part by the Department of Health and Social Security.

Notes

* Originally published in the International Journal of Epidemiology 1977; 6:357–63. The Department of Community Medicine, St Thomas's Hospital and Medical School, London SE1 7EH, England{dagger} and The General Practice, St Paul's Cray, Orpington, Kent.{ddagger} Back

{dagger} WW Holland, AL Cress, MF D'Souza, JRJ Partridge, D Shannon, DH Stone, AV Swan, HT Trevelyan. Back

{dagger}{dagger} E Tuckman and HJT Woodall. Back

References

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3 D'Souza MF, Irwig LM, Trevelyan HT et al. Deafness in middle-age—how big is the problem? Journal of Royal College of General Practitioners 1975;25:472.

4 D'Souza MF, Swan AV, Shannon DJ. Screening for hypertension in general practice. The results of a long-term controlled trial. Lancet 1976;1:1228.[Medline]

5 Holland WW, Trevelyan MH. The value of surveillance and multiphasic screening. Proceedings of the 8th International Congress of Gerontology, Vol 1, 1969.

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9 Wilson JMG, Jungner G. Principles and practice of screening for disease. World Health Organisation, Geneva, 1968.