Diagnostics Flashcards
airport scanners are very
sensitive tests
- they always go off
airport scanners aren’t very
specific
- most who set them off re not carrying a gun
BUT
no one with a gun will get through
often high sensitivity tests
have more specific tests after e.g. one of the more technical airport signals
further tests are usually
time-consuming
expensive
more invasive
example of a sensitive test
HIV testing in blood donor is very sensitive- it is better to throw away a good sample than give infected blood
example of specific test
diagnosing need for kidney transplant is very specific
-it is better not to throw away a good kidney
the important elf a good diagnosis
correct therapy can be used.g. T1 vs T2, which cancer?
early detection
gives better prognosis
diagnosis and screens
a poorly person may visit a doctor- clinical knowledge/ diagnostic tests
an ‘at risk’ population may be
screen- often requires clinical referral and subsequent tests for a diagnosis
what can we use for a diagnostics
something measurable that is different in affected group
symptoms
spots, never, swelling, bleeding
physiology
temp, bp, spirometry, eGFR
Blood-borne
hormone levels, blood glucose, inflammatory mediators, PSA, genetic markers, antibodies
biopsy-based
cancer antigens, cancer histology, leukocytes, genetic markers
what is required for diagnosis
an accurate diagnostic cut-off
the diagnostic cut off lies between
true negatives (healthy) and true positives (diseaseO
Joy’s nose- t shirt sampling smell test for 12 individuals
- 6 diagnosed with parkinson’s
- 1 undiagnosed
- 5 healthy
she was 100% sensitive- no missed cases
and 100% specific- no wrong cases
some people with the disease will be
called negative and some people without the disease will be called positive
VOCs
volatile organic compounds
VOCs are present in
sweat, urine, poo and breath
- metabolic products
- quick, cheap, non-invasive
e. g. dogs smelling for cancer
imaging
e.g. IPF scan, x rays, histology, karyotyping
parameters used in imagine
size, shape, number
- scoring system often used
- subjectivity can be an issue
- expert opinion sometimes required
imaging is…
expensive, timely and generally used as an end diagnostic
automated detection?
e. g. taking photos of a mole
- could help with early detection- better prognosis- cheaper to treat
DNA as a biomarker:
- infection (PCR)
- monogenic disease- sequence candidate genes
- SNps
- cell free (cf) DNA
cell free DNA
e.g circulating tumour (ctDNA)
ctDNA
- liquid biopsy–> PCR –> amplify target genes often mutated in cancer –> DNA sequencing of target regions
- DNA released into blood
- tumour and normal cells
- non-invasive
trisomy screening- current guidelines
11-13 weeks- combined test which is quick and easy
- measure nuchal translucency (PAPP-a_, (HcG) and mother are
- combine to generate risk score
if risk is 1 in 150, amniocentesis is offered
4% risk of miscarriage
- but the gold standard
gold standards are thought to be
diagnostic
new method for detection of trisomy
around 15% of cFDNA in pregnant women comes from embryo cffDNA (cf fatal DNA)
- non invasive rental screen for trisomy
- using NGS- tell us how many copies of DNA
- fetal DNA will be different to maternal DNA
- compares fatal and maternal ratios
new method for detection of trisomy implementation
being introduced tis year, however it is an expensive process, so only higher risk patients (combined test score) referred.
SNPs and GWAS
GWAS correlated the presence of genetic variations (SNPs) with the risk of developing a disease
- identification of an individual SNP profile may indicate risk of developing a condition
e. g. a panel of 18 SNP has been shown to help predict risk of family breast cancer
diagnosing the mind is hard
- how do you get a firm diagnosis of the mind e.g. Trump
- a diagnosis can be classification of behavioural treats
- is there a real condition?
- is it useful to have a diagnosis of internet gaming disorder?
