What will a diagnostic test test the presence of?
A disease, condition or substance.
Participants in a diagnostic test study will present with symptoms already.
What information will a diagnostic test provide?
It collects information that will clarify a patient’s clinical condition, which helps to determine prognosis.
What types of information can be used to help clarify a patient’s clinical continence to help determine prognosis?
Patient characteristics.
Signs and symptoms.
Physical examinations.
Tests that have used laboratory or other technical facilities.
What does the clinical do in a diagnostic test?
They do the test.
They receive the results.
They find out whether the patient has the condition or not.
No diagnostic test is perfect.
Might say a disease isn’t present, when it actually is.
What does a False Positive result mean?
Test says you have it.
But you actually don’t.
What’s a False Negative result mean?
Test says you don’t have it.
But you actually do.
What are practitioners in diagnostic imaging interested in?
Providing high quality images which can permit a medical diagnosis.
What examples of evolving technology are there?
Lymphangiography - this was replaced by US.
Myelography - replaced by CT.
What’s the difference between a diagnostic and a screening test?
Diagnostic -
Generally used when patient has some symptoms that are suggestive of the disease in question.
Screening -
Generally used on people without symptoms, who are drawn from a population with a much lower prevalence of the disease.
What does Screening involve?
Investigating apparently healthy individuals (or asymptomatic), with an aim to identify a disease early, thus enabling earlier intervention and management.
What may Screening involve?
Mass screening of the whole population.
Selected groups will be shown to have an increased risk of prevalence of a certain condition or disease.
What are the 2 types of screening programmes?
Systematic.
Or…
Opportunistic.
What happens in a Systematic Screening Programme?
People are invited.
E.g. mammography study uses female participants aged 50 to 70 years.
What happens in an Opportunistic Screening Programme?
Screening gets offered to someone who may present for a different reason.
E.g. chlamydia screening in a student presenting with depression.
What are some Advantages of Screening?
It can detect unrecognised disease early, meaning their prognosis of the disease can be improved.
E.g. increased survival in women with breast cancer who were diagnosed and treated early.
It can detect individuals that are at high risk of developing a certain disease where the individual or clinician can take measures to delay (or prevent) the development of the disease, done by reducing the risk.
E..g screening for high BP then offering lifestyle advice and/or drug intervention.
It can help identify people with an infectious disease, where an intervention can treat the infection, and prevent transmission of the disease to others.
E.g. chlamydia screening in sexually actively people under the age of 25.
What are some Disadvantages of Screening?
It might give a false sense of security (e.g. if there are some false negative results) and this delays the final diagnosis.
People tested negatively may feel they’ve avoided the disease, so still continue with their risky behaviours.
E.g. individual who eats more than recommended daily allowance of saturated fat may still eat the same amount as when they got tested and were fine, yet it will quickly get worse over time.
This may undermine primary prevention programmes, e.g. to prevent coronary artery disease by promoting healthy eating.
For true positive cases that get early treatment even though the disease is only just starting to develop could create possible side effects.
It can involve lots of medical resources and lots of money, which could be used elsewhere, especially as most people that are screened don’t need treatment.
A false positive result can cause stress and anxiety - and this may be from unnecessary investigations, especially if the procedure is invasive.
Look at onenote for table comparison of diagnostic tests vs screening test.
Diagnostic test results may be ordinary (on a scale) or normal/abnormal.
What is meant by diagnostic test results being Normal/Abnormal -
E.g. the presence or absence of a fracture on a plain radiograph.
What is meant by a Diagnostic Test being Ordinal (on a scale)?
May be classed as something, ranging from a normal mammogram, to one which shows a benign disease, to one that has a suspicion of cancer or the presence of cancer.
It’s important to establish a normal, sensible range.
Boundaries have to be set in order to establish if a test is abnormal or normal.
E.g. blood pressure of 142/92 is abnormal as it’s over 140/90, but is this BP risk different from 138/88?
Treatment needs to be go/no-go decision.
Example of an ordinal diagnostic test result -
Prostate-Specific Antigen -
Healthy man - has 0.5 ng/mol in their blood.
Someone with advanced prostate cancer would show will over 20 ng/mol.
A PSA of 7.4 ng/mol may be found in someone that is normal though, or someone with very early cancer.
So a PSA can’t actually prove if a man has prostate cancer.
However it may increase or decrease the odds of a diagnosis like that.
This is expressed as a likelihood ratio.
Evaluating Health Technologies -
How would you evaluate Diagnostic Technology?
See if the new technology will result in improvements in the prognosis or physical health of the patient.
An imaging investigation should be performed.
And then a clinician will interpret these images.
The clinician will use this info, and other info (clinical findings, other tests), to refine the diagnosis.
The clinician should use this info to plan therapy.
And this may influence patient outcome.
