Despite evident benefits in population screening, such programmes are slow to develop. From the mobile x-ray vans of the 1960's, and the breast and cervical screening systems established over the last 20 years, the only other screening tests established throughout the UK are those for neonatal screening for thyroid disease and PKU, and second trimester testing of pregnant women for evidence of foetal abnormalities.
The use of tests to screen populations for abnormalities is a subject which raises strong views on both sides of the argument. Clearly, tests which have published normal ranges that are truncated from the normal distribution of results will, if applied to a normal population, throw up seemingly abnormal values which are not indicative of an underlying disease. On the other hand, early diagnosis of conditions such as Diabetes can have a significant impact on quality of life and the avoidance of the costs associated with the sequelae of the untreated condition.
As the Chief Medical Officer for England, Sir Kenneth Calman has said, 'we must be clear that there are both benefits and limitations to population screening. A screening test is not a diagnostic test. It is applied to (apparently) healthy people in order that a small percentage who might develop a disease can be identified and subsequently diagnosed and treated.'
Therefore, whilst the diagnostics industry has made great strides forward in health screening technologies, the prospects of introduction of national screening programmes funded by central government continue to be debated. New screening tests for risk of onset of osteoporosis - simple, cost-effective laboratory tests to measure lipids in patients at risk of heart disease - new dip-stick tests for assessment of kidney function - these, and many more may well remain "under consideration" by the NHS.
The major problem is one of pay-back. Quite simply, the investment today will take many years to produce the cost-savings screening promises. Budgets are tight, and the government, quite rightly, will examine the cost/benefit ratio at its leisure.
The cost of screening the at-risk population for diabetes has been shown to be less than the costs associated with the complications resulting from lack of timely diagnosis(1) and the King’s Fund has called for screening on this basis(2). In the case of diabetes, the benefits are not restricted to reducing the impact on secondary care, for as Nichols et al reported at the 59th symposium of the American Diabetes Association last year, medical costs in primary care soar before diagnosis. Based on the healthcare records of more than 8600 individuals who were subsequently diagnosed with Type 2 diabetes, healthcare resources were used more frequently up to eight years prior to diagnosis. This was shown to be a 62% increase in the final three years, compared to a control group not subsequently diagnosed as diabetic. Medical costs significantly increased during this period, showing a 53% increase in the final two years prior to diagnosis.
What other conditions offer the opportunity to apply targeted in vitro diagnostic screening in order to gain downstream savings in resources and quality of life?
Researchers in the Group Health Centre in Puget Sound, USA, found a 56% reduction in the incidence of acute pelvic inflammatory disease following implementation of a targeted programme of testing for Chlamydia infection, this condition costs the US Health Budget $2,000,000,000 annually. Screening for Chlamydia with DNA probe technology in Sweden reduced prevalence of PID by a factor of five over seven years. In addition, some 50% of female infertility is caused by this infection, reducing the incidence also must offer benefits in this area. Without doubt, screening for this condition reduces the incidence many fold(3) and treatment is straightforward.
A similar argument can be made for testing individuals symptomatic for gastric infections of Helicobacter pylori, responsible for 90% of gastric ulcers and estimated to affect one million individuals in the UK. Simple to treat, this condition if left to its own devices can result in hospitalisation, and on occasion, death from complications. Near patient tests for both antibodies to, and the presence of, H.pylori are available.
There are two keys to successful screening, effective targeting of the populations at risk, and evidence of positive outcomes to diagnosis, measured by quality of life of the individual affected and/or downstream savings to the healthcare budget.
The benefits of the use of prostate-specific antigen (PSA) to screen for prostate cancer remain controversial, and although it is still too early to measure directly the effects of PSA screening on mortality, workers in the United States are examining data to determine if there is other evidence of the effectiveness of PSA as a screening tool. They found that changes in the epidemiology of prostate cancer since the advent of the PSA era are consistent with the introduction of an effective screening test. This is evidenced by an increase in detection of significant prostate cancer in individuals who will likely benefit from treatment(4).
A great deal of interest has been shown recently in the role of diagnostics in the analysis of risk factors for osteoporosis, a condition likely to affect over 30% of women, exacerbated by the expected increase in the elderly population over the next few decades(5).
There are many more conditions which can be discussed in this vein, and a recent technology which offers a new opportunity to predict and prevent disease ensues from genetic research. For good or ill, the ability to predict the likelihood of genetically mediated conditions will become relatively simple and inexpensive as this decade unfolds. Already the public is aware of tests for certain inherited conditions, or inherited risk factors associated with disease. The primary care physician will soon need to contemplate which of these are supported in the evidence, and also come to terms with pharmacogenomic issues relating to genetic propensity to response to medication.
As the pressure builds on reducing waiting lists in secondary care, the benefits of appropriate public screening programmes, run by the NHS will be seen in the long term through the ability to diagnose conditions early enough to avoid hospitalisation. New technologies will also provide individuals more opportunity to pay for his own screening, through an increasing array of devices and testing services.
Whether provided through public service programme, clinics or self testing, screening will provide the GP with information on the health of his patients often before the onset of overt symptoms. A new paradigm for managing such individuals will need to be set as he is no longer treating the sick but in effect keeping people healthy.
- JAMA (1998) 280:1757
- King's Fund Policy Institute's report Counting the Cost: The Real Impact of Non Insulin Dependant Diabetes,1998
- New England Journal of Medicine(1996)334,1362-1366
- Urology 1998 Sep;52(3):444-8; discussion 448-9
- Osteoporosis Position Paper 1999, British In Vitro Diagnostics Association