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.
References
Grimes DA and Schulz KF.
(2002). Uses and abuses of screening tests. The
Lancet.
Moran PS et al. (2013).
Effectiveness of systematic screening for the detection of atrial fibrillation.
Cochrane Reviews.
Greenhalgh T (1997).
Papers that report diagnostic or screening tests. British Medical Journal.
