What is a screening test?
Screening tests are commonly used in medical practice to help identify those at an increased risk of having a particular disease. While it is widely thought that a screening test is diagnostic, it is given to healthy people without symptoms to detect who are likely to have or develop the disease.
A screening test will either produce a negative or positive result. A negative result means there is a low risk of having the condition screened for at the moment. It does not mean the condition will never be developed. A positive result means there is a higher risk of having the condition screened for at the moment.
Those who have positive results from a screening program will be offered further tests to confirm diagnosis of the condition.
Validity of a screening test
A test is valid if it detects most people with the condition and excludes most people without the condition. It is very unlikely that a screening test is 100% accurate. This means that there can be false positives or false negatives – a false positive may cause a person to worry unnecessarily and a false negative may mislead a person that he/she is healthy when actually diseased.
Not all conditions will be screened for. Screening tests are very expensive and will often only be implemented where there is a high prevalence of disease. For screening to be worthwhile, it needs to increase the detection of positive cases as well as benefit those who are detected with the condition.
For example, pancreatic cancer has a low prevalence and is usually only diagnosed in the late stages of disease, meaning likelihood of survival is low. A screening test would not be implemented for this disease, because the majority of cases are already in the late stage and there is little benefit screening could produce.
Benefits of screening tests
The aim of screening is to offer it to the people who are most likely going to benefit from it. Identifying a health condition early on can mean that treatment is more effective and negative impact from condition can be minimized.
An example of this is demonstrated through screening tests for heart disease. There is significant evidence that giving an electrocardiogram (ECG) screening test to everyone over 65 can increased the number of detected cases. By detecting cases before a severe heart condition develops, patients are able to be aware of their risk and monitor it more closely.
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