Autoimmunity diagnosis Flashcards
What are the 2 general principles of diagnostic testing?
1) Diagnostic tests should be used to answer specific questions and/or to support a clinical diagnosis, but not as a screening tool
2) The ability of tests to correctly discriminate between health and disease is improved when they are used in the appropriate population
What is the definition of specificity, how is it calculated?
Measure of how good the test is in identifying people with the disease
Calculated by:
correctly identified positives/all people with the disease
What is the definition of specificity and how is it calculated?
Measure of how good the test is at correctly defining people without the disease
Calculated by:
correctly identified negatives/all people without the disease
What is the definition of positive predictive value, how is it calculated?
The proportion of people with a positive test who actually have the disease
Calculated by:
correctly identified positives/ all positive test results
What is the definition of negative predictive value, how is it calculated?
The proportion of people with a negative test who do not have the target disorder
Calculated by:
correctly identified negatives/all negative test results
What are the 2 general types of diagnostic test?
1) Non specific
2) Disease specific
Most non specific diagnostic tests identify what?
Inflammatory markers
Give 2 types of disease specific diagnostic tests?
1) Autoantibody testing
2) HLA typing
Give 7 non specific markers of systemic inflammation?
1) ESR
2) CRP
3) Ferritin
4) Fibrinogen
5) Haptoglobin
6) Albumin
7) Complement
CRP is produced in what organ when, what is it useful for?
Produced by the liver in acute inflammatory response
Rapidly produced and rapidly used up so useful for monitoring response to treatment at close intervals
What is ESR, how is it useful as a marker of inflammation?
Erythrocyte sedimentation rate - viscosity of the plasma is higher in inflammation so erythrocytes take longer to fall to the bottom of a test tube of blood. Not an acute measure, gives you an idea of inflammation being present for a number of weeks
What happens to levels of ferritin and fibrinogen in inflammation?
Increase in acute inflammatory response
What happens to levels of albumin in inflammation?
Decrease - synthetic production by liver decreases due to production of other substances in inflammation
What are Antinuclear Ab? (ANA)
Auto-Ab which recognise structures or substances found in the nucleus of cells - involved in alot of autoimmune diseases
What is meant by Extractable nuclear antigens (ENAs)?
Structures found in the nucleus which are the specific targets of different types of Anti-nuclear Ab
Give 4 examples of extractable nuclear Ags?
1) RNP - ribonuclear protein (Ro and La are types of RNPs)
4) Double stranded DNA
How do we detect ANAs?
Use large fibrocyte type cells - they have a large nucleus Spread them along the microscope slide and incubate with patients serum
If ANA is present in the serum it will bind to the cells
You can visualise these bound ANAs using a second Ab with a fluorescent marker which binds to the constant Fc region
Thus by visualising the fluoresence you can detect the presence of ANAs in the serum
How can the results of testing for ANAs help us to narrow down the likely specific target and thus the specific autoimmune diseases those targets are associated with?
The pattern of fluorescence eg. homogenous (whole nucleus all the same), speckled, centromere, nucleolar, peripheral, is different for different ANA targets
Anti-DNA ANAs are likely to give what kind of fluorescent pattern?
Peripheral or homogenous
Anti-histone and anti-DNP ANAs are likely to give what kind of fluorescent pattern?
Homogenous
Anti-Ro and Anti-La ANAs are likely to give what kind of fluorescent pattern?
Speckled
Give 3 assays used to test for Anti-dsDNA Ab?
1) Cirthida luciliae assay
2) Farr assay
3) ELISA
Give 3 techniques used to identify ENA (extractable nuclear Ags)?
1) Immunoblots
2) Individual ELISA’s
3) Combination of antigens
How many different Ab have been described in SLE?
> 100
How does a microbead-based immunoassay to identify non-organ specific autoantibodies work?
1) Have beads with a unique internal colour which can be recognised by a machine and gives them a unique identity
2) To each bead you can attach a certain Ag you want to measure
3) Incubate these beads with patient serum
4) If auto-Ab are present they will attach to the bead with their specific target Ag
5) Use a second fluorescently labelled Ab which binds to any bound auto-Ab
6) Put beads through a machine, tells you which bead it is (ie. which specific Ag) and whether anything is attached
dsDNA (antigen) is highly specific for what?
SLE - often correlates with active severe disease
What is rheumatoid factor?
An the auto-Ab directed against the Fc portion of IgG
What role does rheumatoid factor have in rheumatoid arthritis?
Commonly found in rheumatoid arthritis, RF and IgG join to form immune complexes which contribute to the immune process
What are the sensitivity and specificity of rheumatoid factor for rheumatoid arthritis?
Around 70%
Other that rheumatoid arthritis, what other conditions can rheumatoid factor be seen in?
Can be seen in other diseases in which polyclonal stimulation of B cells is seen (chronic infections such as Hep B)
High concentrations of RF can be pathogenic in what disease?
Vasculitis
What biomarker is more specific for rheumatoid arthritis than rheumatoid factor?
Anti-CCP
95% specific, similar sensitivity to RF
Other than in aiding diagnosis of rheumatoid arthritis what else is measuring Anti-CPP useful for?
Anti-CPP is a useful prognostic marker
Anti-CCP (ACPA) positive patients tend to have more severe and erosive disease
Anti-neutrophilic cytoplasmic Ab (ANCA) were first described as an auto Ab specific for what?
Wegeners granulomatosis
Cytoplasmic (c)ANCAs show what fluorescent pattern?
granular fluorescence of neutrophil cytoplasm with nuclear sparing
What are the 4 most common target Ag for (c)ANCAs?
1) PR3 (90%)
2) Azurocidin
3) Lysozyme (1%)
4) MPO
Perinuclear (p)ANCAs show what fluorescent pattern?
Apparent fluorescence of the nucleus only
What are the 5 most common Ag for (p)ANCAs?
1) MPO (70%)
2) Azurocidin
3) B-glucuronidase
4) Cathepsin G (5%)
5) PR3
Name 3 ANCA associated systemic vasculitidies (AAV)?
1) Granulomatosis with polyangitis (Wegener’s granulomatosis)
2) Microscopic polyangitis
3) Churg-Strauss syndrome
In Wegener’s granulomatosis which Ag is more common, PR3 or MPO?
PR3 much more common than MPO
In microscopic polyangitis which Ag is more common PR3 or MPO?
MPO is more common than PR3
In Churg-Strauss syndrome which Ag is more common, MPO or PR3?
MPO is more common than PR3
Anti-neutrophilic cytoplasmic antibodies are associated with what conditions?
Anti-neutrophilic cytoplasmic Ab associated vasculitidies
ANCA positivity is highest in which ANCA associated vasculitis?
Wegener’s granulomatosis followed by microscopic polyangitis followed by Churg-Strauss syndrome
What is the gold standard diagnosis for ANCA associated vasculitidies?
Histopathology
Does ANCA testing have a role to play in diagnosing ANCA associated vasculidities?
Yes, useful for suggesting the diagnosis in the proper clinical setting but not gold standard
Do negative ANCA assays exclude AASV (ANCA associated systemic vasculitidities)?
No since 10-15% of AASV patients will be ANCA negative
If a patient has a positive ANCA result but no clinical indications of active disease would you continue to treat them?
No
What does re-emergence of ANCA positive in a patient who was ANCA negative in remission suggest?
A risk of disease flare
What Ab is found specifically in primary biliary sclerosis?
1) Anti-mitochondrial Ab
What 4 Abs are found in autoimmune hepatitis?
1) Anti-smooth muscle Ab
2) Anti liver/kidney/microsomal (LKS) Abs
Name 4 Ab found in Type I DM?
1) Islet cell Ab
2) anti-GAD 65 and anti-GAD67
3) anti-insulinoma antigen 2 (IA-2)
4) insulin autoantibodies (IAAs)
What happens to the auto-Ab found in type I DM as the disease progresses?
The auto-Ab disappear with progression of the disease and total destruction of beta islet cells
What is the role of auto-Ab in diagnosis of type I DM? 4
1) Disease conformation
2) To identify relatives and patients at risk of developing autoimmune diabetes
3) Negative predictive value of ICA and IAA is almost 99%
4) Increased risk of disease development with greater number of different auto-Ab present and younger age of patient
