Case Unit 6: Diagnostics Flashcards
What is the specificity of a diagnostic test?
The probability that someone without the disease will test negative
How is specificity calculated
(True Negatives)/(True Negatives + False positives)
What is the sensitivity of a diagnostic test?
The probability that someone with the disease will test positive
How is sensitivity calculated
(True Positives)/(True Positives + False negatives)
What is positive predictive value?
Proportion of positive results that are true positives
How is positive predictive value calculated?
(Number of people with disease who test positive)/(Total number who test positive)
What is negative predictive value?
Proportion of negative results that are true negatives
How is negative predictive value calculated?
(Number of people without disease who test negative)/(Total number who test negative)
What is the difference between a diagnosis and a screen?
Diagnosis when there are symptoms
At-risk populations can be screened even when presenting no symptoms
What is a diagnostic cut-off?
A value from a diagnostic test that anything above indicates disease and anything below indicates the patient is healthy.
What are VOCs?
Volatile Organic Compounds
Metabolic products produced by people with disease, not produced by those without
Advantages and limitations of using VOCs as a diagnostic markers?
Quick to test, cheap to test, non-invasive
What are the types of imaging diagnostic tools?
X-Rays
Histology - looking at biopsies
Karyotyping
Advantages and limitations of imaging as a diagnostic tool?
Invasive - may require biopsy
Expensive
Subjectivity of the person who is viewing it
How can DNA be used as a biomarker?
Gene sequencing
Cell free DNA
SNPs
Advantages and limitations of DNA as a diagnostic biomarker?
Non-invasive (liquid biopsy)
Can test for many genes at once
What is cell free DNA?
DNA circulating in blood
Released from necrosing cells, damaged cells, tumour cells
Sampled using liquid biopsy
How is cell free DNA analysed?
Take liquid biopsy
Purify cell free DNA
Use PCR to amplify genes that are commonly mutated in cancer
Advantages and limitations of using genetic variation as a diagnostic biomarker?
SNPs can indicate risk of developing a condition
Useful flag for indicating increased risk of disease
What is DNA sequencing?
Determining the order of nucleotides in a DNA molecule
- Used to detect mutations/test for a genetic disease
- Analyse products of RNA seq to determine level of gene expression
