Medical screening

Screening

Screening is defined as the presumptive identification of unrecognized disease in an apparently healthy, asymptomatic population by means of tests, examinations or other procedures that can be applied rapidly and easily to the target population. A screening programme must include all the core components in the screening process from inviting the target population to accessing effective treatment for individuals diagnosed with disease.

Screening is a process – one that begins with invitation to participate and ends with treatment for appropriately identified individuals. An effective screening programme should meet the following criteria: 

1.Mechanisms for systematic invitation and follow-up for individuals identified by the screening test as having an abnormal finding (call and recall mechanisms);

2.Participation of over 70% of the target population to be screened; 

3.Necessary infrastructure and resources to offer the test periodically and to adequately diagnose and treat those found to have cancer or a precancerous lesion, and; 

4.Robust monitoring and evaluation framework to assure quality.

Types of screening.

• Mass screening: The screening of a whole population or subgroup. It is offered to all, irrespective of the risk status of the individual.
• High risk or selective screening: High risk screening is conducted only among at-risk populations.
• Multiphasic screening: The application of two or more screening tests to a large population at one time, instead of carrying out separate screening tests for single diseases.
• When done thoughtfully and based on research, identification of risk factors can be a strategy for medical screening.

Purpose of Screening Programmes

 1. Screening is designed to identify those people who have the early stages of a disease or an increased chance of developing a disease or condition. The purpose of screening includes:

2. To save lives by treating disease in their early stages, thereby increasing the survival chances of the patient

3. Improving the quality of the patient’s life through early identification

4. Reducing the chance of developing the disease/halting disease progression by allowing the patient to make life changes

5.Saving money for the NHS by treating in early stages rather than later, complicated stages

6.To aid in meeting NHS targets for disease elimination/detection

Characteristics of a Good Screening Test.

• Inexpensive
• Easy to administer
• Minimal discomfort
• Reliable (consistent)
• Valid (distinguishes diseased & non-diseased people).

 

Test validity 

is the ability of a screening test to accurately identify diseased and non-disease individuals. An ideal screening test is exquisitely sensitive (high probability of detecting disease) and extremely specific (high probability that those without the disease will screen negative). However, there is rarely a clean distinction between "normal" and "abnormal”

The validity of a screening test is based on its accuracy in identifying diseased and non-diseased persons, and this can only be determined if the accuracy of the screening test can be compared to some "gold standard" that establishes the true disease status. The gold standard might be a very accurate, but more expensive diagnostic test. 

Sensitivity

One measure of test validity is sensitivity, i.e., how accurate the screening test is in identifying disease in people who truly have the disease. When thinking about sensitivity, focus on the individuals who, in fact, really were diseased.

Specificity

Specificity focuses on the accuracy of the screening test in correctly classifying truly non-diseased people. It is the probability that non-diseased subjects will be classified as normal by the screening test.

Many people use the terms screening and diagnosis interchangeably. They are not the same. 

Screening tests are used for a presumptive identification of an unrecognized disease or illness.

Diagnostic tests, on the other hand, are used to determine the presence or absence of a disease when the patient is showing symptoms of the disease OR has been targeted through a positive screening test. In some circumstances, the same test can function as either a screening or diagnostic test.

 

Screening results.

If you get a normal result (a screen negative result) after a screening test, this means you are at low risk of having the condition you were screened for. This does not mean you will never develop the condition in the future, just that you are low risk at the moment.

If you have a higher-risk result (a screen positive result), it means you may have the condition that you've been tested for. At this point, you will be offered further tests (called diagnostic tests) to confirm if you have the condition. You can then be offered treatment, advice and support.

Limitations

Ethics can present a challenge, as the programme tests apparently healthy individuals. It must be ensured that these people receive guidance to make an informed choice and must be given support. Expectations of the patient must be realistic about what the programme can do – screening does not guarantee protection or that the condition will not develop after testing. Also, all screening tests will produce some false positive and false negative results.