(9) Autoimmunity Diagnosis Flashcards
(59 cards)
Should diagnostic tests be used as screening tools?
No
They should be used to answer specific questions and/or to support a clinical diagnosis but not as screening tools
When is the ability of a diagnostic test to correctly discriminate between health and disease improved?
When they are used in the appropriate population
What is ‘sensitivity’?
Measure of how good the test is in identifying people with the disease
a/(a+c)
What is ‘specificity’?
Measure of how good the test is at correctly defining people without the disease
d/(b+d)
What is ‘positive predictive value’?
The proportion of people with a positive test who have the target disorder
a/(a+b)
What is the ‘negative predictive value’?
The proportion of people with a negative test who do not have the target disorder
d/(c+d)
What graph can be used to give you an idea as to whether a diagnostic test would be valuable?
A normogram
What is the likelihood ratio (LR)? (used in a normogram)
probability of finding in patients with the disease / probability of same finding in patients without disease
The higher the LR, the more useful the test
What are the 3 parts of a normogram that should be connected by a line?
- pre-test probability
- likelihood ratio
- post-test probability
Give a type of non-specific diagnostic test
Inflammatory markers
Give 2 types of disease-specific diagnostic test
- autoantibody testing
- HLA typing
Give examples of non-specific markers of systemic inflammation
- ESR
- CRP
- ferritin
- haptoglobin
- albumin
- complement
(acute phase response proteins)
What are acute phase response proteins?
Class of proteins whose plasma concentrations increase (positive acute-phase proteins) or decrease (negative acute-phase proteins) in response to inflammation
How is C-reactive protein (CRP) an inflammatory marker?
Produced by liver after infection/inflammation
Changes acutely and so useful to measure treatment within 24 hours
What is ESR and how is it an inflammatory marker?
Erythrocyte sedimentation rate
Measures viscosity of plasma - viscosity increases after an inflammatory response
ESR takes a while to fully resolve after the infection + treatment
Does albumin (an inflammatory marker) increase or decrease in acute inflammation?
Goes down
Synthetic capacity of liver reduces
What are origins of ANA (antinuclear antibodies)?
LE phenomena in 1948
dsDNA identified in 1957
Anti-SM in 1966
What was noticed when bone marrow was taken and looked at from an SLE patient?
The nuclei of the erythrocytes had been engulfed by neutrophils and macrophages
What was noticed when the serum of an SLE patient was analysed?
Antibodies against double-stranded DNA (dsDNA) were present - autoantibodies directed to the nucleus
What are some possible specific targets of autoantibodies?
- double stranded DNA (dsDNA)
- RNP (ribonuclear proteins, protein machinery that deals with dsDNA transcription and translation)
- Ro (RNP)
- La (RNP)
What does ENA stand for?
Extractable nuclear antigens
These include the things that autoantibodies might be specifically targeted to
When might you ask for an ANA detection test?
Patient with hair loss, mouth ulcers, joint pain etc. Diagnostic test to confirm suspicions of lupus
What does an ANA detection test do?
It looks for autoantibodies against the nucleus in the serum
Why are secondary antibodies used in an ANA detection test?
They are used for visualisation - fluorescently tagged
They recognise the constant fc region of the ig molecule
Can see it brightly where there are autoantibodies against the nucleus
