In short
More screening is not better screening. A test earns its place only if it passes three tests of its own.
- Does the condition cause real harm, and often enough in someone like you?
- Does finding it early lead to better outcomes than finding it when symptoms appear?
- Is the test sensitive and specific enough not to generate more harm than it prevents?
Screening that fails any one of these can still look impressive, because three well known statistical illusions make useless screening appear to work.
Condition Overview
Why is more testing not automatically better?
Because a doctor who initiates screening is in a different position from one who responds to a complaint. As Cochrane and Holland put it in 1971, if you start screening you should have conclusive evidence that it alters the course of disease in a meaningful proportion of those screened.
That is a high bar, and plenty of popular tests do not clear it.
What are the three criteria?
| Burden of suffering | The condition must cause real harm and occur often enough in people like you. Breast cancer incidence is about 1.8 per 100,000 in women in their early 20s, which is why it is not screened for at that age. |
| Effective treatment | Treating it early must beat treating it when symptoms appear. If the outcome is the same either way, screening adds nothing. |
| Test performance | Sensitive enough not to miss cases, specific enough not to send healthy people down a chain of further tests. |
Why does bad screening look good?
Three biases, and they are the reason clinics can show you impressive survival figures for tests that save no lives.
- Lead time bias. Find a disease earlier and survival from diagnosis lengthens automatically, even if the date of death does not move. That is not extra life, it is extra time knowing.
- Length time bias. Screening preferentially catches slow growing tumours, because they sit there longer waiting to be found. Fast ones show up as symptoms between screens. So screen detected disease looks better behaved.
- Adherence bias. People who turn up for things do better anyway. In one trial, people in the placebo arm who took at least 75 per cent of their dummy pills had half the mortality of those who took fewer.
What separates real evidence from these illusions?
Mortality rates in a randomised comparison, not survival rates in a screened group. That is why breast, colorectal and lung cancer screening are recommended: randomised trials showed lower death rates, not longer survival times.
Lung cancer is the cleanest example. Chest x ray and sputum screening was tested and failed, and 20 years later death rates were the same. Only in 2011 did low dose CT show a 20 per cent reduction in lung cancer deaths.
What is overdiagnosis?
Finding disease that would never have harmed you. Prostate cancer is the standard illustration: autopsy studies found it in 5 per cent of men in their 20s, 30 per cent in their 50s and 83 per cent in their 70s.
Most of that would never have become invasive. A test that finds it can look highly sensitive while mostly detecting things that were never going to matter.
When to See a Doctor
- You want a screening plan matched to your age and risks rather than a package chosen by price
- You have been offered a long panel of tests and want to know which of them actually change outcomes
- A result from a previous check has been flagged and you are not sure whether it needs chasing
- You have a family history that might change which tests are appropriate for you
- You are due for age appropriate cancer screening and want it organised properly
- Any new symptom, which needs assessment as a symptom rather than being folded into a screening package
- Unexplained weight loss, bleeding, a lump, or a persistent change in bowel or bladder habit
- Chest pain or breathlessness on exertion
How Dr. Felix Assesses This
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1
Who you are and what you are actually at risk of
Age, sex, family history, smoking history, existing conditions and previous results. Risk determines which tests are worth doing, because incidence is low for most conditions in most people.
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2
Which tests clear the three criteria for you
Each proposed test is checked against burden of suffering, effectiveness of early treatment and test performance in someone with your risk. Tests that fail are named and left out.
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3
What each result would mean before it is ordered
Including what happens if it comes back borderline. A test whose abnormal result would not change anything is not ordered.
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4
A schedule, not a one off
Screening intervals are set. The yield of a first screen is always higher than later ones, so the interpretation of a repeat differs from the first.
Treatment Options
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Women’s Executive Check
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Why Early Treatment Can Matter
Where does screening genuinely save lives?
- Colorectal cancer. In a large case control study, colonoscopy followed by early treatment prevented about two thirds of colorectal cancer deaths
- Lung cancer in smokers. Low dose CT reduced lung cancer mortality by 20 per cent at a median 6.5 years
- Breast cancer. Randomised trials show lower mortality in screened women of the appropriate age
- Cardiovascular risk. Blood pressure and lipid treatment are backed by randomised trials, and treatment is targeted using calculated risk
Where the evidence is weaker
Behavioural counselling is not held to the same regulatory standard as drugs, so it needs checking case by case. Smoking cessation counselling is the exception with strong evidence, raising quit rates by more than half across 49 trials.
Vitamins, minerals and supplements are rarely tested in randomised trials at all, because nobody has to test them.
What about the harms?
False positives are the main one. They lead to further tests, procedures and anxiety, and in a low prevalence population most positive results in a poor test will be false.
The yield also falls after the first round. The first screen picks up everything that has accumulated over years, so later rounds find fewer cases and a higher proportion of positives are false.
Why Early Treatment Can Matter
Where does screening genuinely save lives?
- Colorectal cancer. In a large case control study, colonoscopy followed by early treatment prevented about two thirds of colorectal cancer deaths
- Lung cancer in smokers. Low dose CT reduced lung cancer mortality by 20 per cent at a median 6.5 years
- Breast cancer. Randomised trials show lower mortality in screened women of the appropriate age
- Cardiovascular risk. Blood pressure and lipid treatment are backed by randomised trials, and treatment is targeted using calculated risk
Where the evidence is weaker
Behavioural counselling is not held to the same regulatory standard as drugs, so it needs checking case by case. Smoking cessation counselling is the exception with strong evidence, raising quit rates by more than half across 49 trials.
Vitamins, minerals and supplements are rarely tested in randomised trials at all, because nobody has to test them.
What about the harms?
False positives are the main one. They lead to further tests, procedures and anxiety, and in a low prevalence population most positive results in a poor test will be false.
The yield also falls after the first round. The first screen picks up everything that has accumulated over years, so later rounds find fewer cases and a higher proportion of positives are false.
What good screening delivers
Colonoscopy prevented about two thirds of colorectal cancer deaths. Low dose CT cut lung cancer mortality by 20 per cent in the right group.
What bad screening costs
False positives, further procedures, and overdiagnosis of disease that would never have caused harm.
Fewer, better tests
A short plan matched to your age and risk, with the reason for each test stated before it is ordered.
Cost & Consultation Investment
The consultation is quoted individually, and each test is quoted before it is ordered. There is no fixed screening package, because the right set of tests depends on your age and risks rather than on a price tier. Tests that would not change anything for you are named and left out rather than added to make a package look comprehensive.
Frequently Asked Questions
Rarely. It finds a great many things that were never going to matter, each of which then needs excluding. The three criteria for screening are not met for most of what such a scan looks at.
Because in a group without symptoms most conditions are rare, so most positive results from a weak test are false. Each one leads to further testing with its own risks.
Survival from diagnosis is the wrong measure. Screening lengthens it automatically by moving the diagnosis earlier, without moving the date of death. What counts is a lower death rate in a randomised comparison.
Finding a disease that would never have harmed you. Autopsy studies found prostate cancer in 30 per cent of men in their 50s and 83 per cent in their 70s, most of which would never have become invasive.
It depends on your age, sex, family history and risk factors. Cardiovascular risk assessment, age appropriate cancer screening and a short blood panel are the usual core, and each is justified before it is ordered.
It varies by test and by your risk. Cardiovascular risk is reassessed every four to six years if you are low risk and yearly if not. Cancer screening follows the intervals set for your age group.
It means that specific condition was not found by that specific test at that moment. It says nothing about anything the test was not looking for, which is why the plan matters more than the result.
Evidence
Where this information comes from
Every figure on this page is taken from the sources below. All of them are free to read, so you can check them yourself.
- Cardiovascular diseases
- Cardiovascular disease: risk assessment and reduction
- Hypertension in adults: diagnosis and management
This page is general medical information and does not replace a personal consultation. Trial results are averages across large groups, not a prediction for any one person.