Detecting disease or risk factors for a disease before symptoms develop
Screening is an important element of preventive medicine. Most screening tests are used to detect risk factors associated with disease or to make an early diagnosis of a treatable condition. Less commonly, if there is a rare inherited disease in your family history, screening may be carried out to find out if you have an abnormal gene that could cause a disorder in you or your children.
You may be offered screening tests at different stages of your life. A few tests are offered to women as part of national screening programmes, while others are available on request or might be recommended if there are risk factors which predispose you to a particular disease.
Before accepting a test, you should ask your doctor what it involves, if it carries risks, and how reliable it is. You should also consider the possible implications of the test results. No test is completely accurate, and sometimes a test can miss disease or suggest disease when it is not present. An abnormal result may lead to further investigations for which you might not be prepared.
Why people are screened
It is not possible or even worthwhile to screen for every risk factor or disease. Tests are useful only if they detect a disease or risk factor that can be treated effectively, and which benefits from early treatment. For example, women are screened for cervical abnormalities such as cervical intraepithelial neoplasia that can be treated before cancer of the cervix develops.
Some screening tests are offered to adults at stages of life when the risk of certain diseases increases (see Common screening tests). You may be offered other tests if you have a higher than normal risk of a disorder due to factors in your lifestyle such as heavy smoking, your age, family history of disease, or a pre-existing illness that increases the risk of other disorders.
Stage of life
Your risk of developing certain disorders depends on your age. For this reason, the type and frequency of screening tests that your doctor may recommend will change as you grow older. Women are offered a specific programme of tests during pregnancy (see Routine antenatal care), in which they are tested regularly for conditions such as pre-eclampsia (see Pre-eclampsia and eclampsia) or diabetes mellitus that can be harmful to the mother or the baby or both. The fetus may also be screened by ultrasound (see Ultrasound scanning in pregnancy) for abnormalities such as heart disorders that may require treatment after birth.
Screening for early signs of breast cancer and cervical cancer is offered on the NHS to women in specific age groups. Cervical cancer screening is offered to women every 3–5 years from the age of 20 or 25 until the age of 60 or 65 (the ages at which screening starts and ends vary depending on where you live). Mammography to screen for breast cancer is offered to women every 3 years from age 50 to age 70. The faecal occult blood test to screen for colorectal cancer is offered to men and women every 2 years from the age of 50 or 60 to the age of 69 or 74 (again, the start and end ages vary according to where you live). One of the most common screening tests carried out is blood pressure measurement, because high blood pressure (see Hypertension) itself is symptomless but is a major risk factor for heart disease and stroke. Blood pressure is usually measured in the doctor’s surgery, often when you see the doctor for another health problem.
A number of disorders, including abnormally high levels of cholesterol and other lipids in the blood (see Inherited hyperlipidaemias), colorectal cancer, and breast cancer, tend to run in families. If any members of your family have been affected by one of these disorders, your doctor may suggest screening tests to look for early disease. For example you may be offered regular faecal occult blood tests earlier than normal if you have a family history of colorectal cancer. A woman with a family history of breast cancer, may be offered breast X-rays (see Mammography) earlier or more often than is usual. Particular forms of breast cancer are known to be caused by inherited faulty genes. There are tests that can identify specific abnormal genes.
If you have a long-term disorder, you may be offered regular screening to detect early signs of complications. For example, people with diabetes mellitus are screened routinely for kidney disease, cardiovascular disorders, nerve damage, and damage to the blood vessels of the eye.
In some occupations, workers are exposed to dust or toxins that can increase the risk of some diseases. If your occupation carries known health risks, take appropriate safety measures (see Safety and health at work) and participate in any screening offered by your employer.
Who carries out screening?
Most screening is carried out at your doctor’s surgery or at special clinics. Your doctor may refer you to a specialist for certain tests, such as colonoscopy.
There are several simple health checks that you can regularly perform yourself to help detect early indications of disease. They include breast awareness, examining the testes, and inspecting the skin for signs of skin cancer (see Checking your skin). If you discover any abnormal signs, discuss them with your doctor as soon as possible. Although you can now buy screening test kits for some disorders over the counter, such kits do not always produce accurate results. Furthermore, the significance of the results in your individual case may need expert interpretation and you are therefore advised to always consult your doctor if you are concerned about a health risk. He or she will arrange for appropriate tests and advise you about any further tests you may need.
Your test results
Some tests, such as those for metabolic disorders in children (see Blood spot screening tests), produce a clear positive or negative result that does not usually require further investigation. The results of other tests may not be as easy to interpret.
If your test results are negative, no further action may be needed until the next screening test. No screening test is 100 per cent accurate, and, rarely, a disorder may be present even though test results were negative. When this happens, the result is called a false-negative.
Sometimes a disease develops soon after a test: if symptoms become apparent, consult your doctor even if your test result was negative. You will be advised if further action is needed. In most cases, regular screening tests pick up diseases before symptoms develop.
If your result is positive, your doctor may repeat the test or arrange for further investigations to confirm the result and perhaps provide more information. For example, if a mammogram reveals an abnormality, a test in which a sample of cells is collected (see Fine-needle aspiration of a breast lump) may be needed to find out the cause.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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