Diagnosis of autoimmune diseases Flashcards
What is the sensitivity of a test
How good the test is for identifying people with the disease
Specificity
Measure of how good the test is at defining people without disease
Positive predictive value
Proportion of positive tests with disorder
Negative predictive value
Proportion of negatives without disorder
Types of diagnostic test
Non-specific - inflammatory markers
Disease specific - Autoantibody testing, HLA typing
Non-specific markers of systemic inflammation
Inflammatory markers:
ESR, CRP, albumin, complement etc
What are Antinuclear antibodies
- Antibodies produced by patient in blood that binds to cell nucleus
How does the ANA test work
- Put an antigen on a plate, separate the patient’s serum. Put serum over the plate and if antibodies present they will bind
- Add an antibody with a light up label to the antibody
- Put under fluorescent microscope to see if it’s lit
Detection of dsDNA and ANA’s techniques
Anti-dsDNA: Farr assay, ELISA, protozoa
ANA’s: Immunoblots
SLE diagnosis with autoantibody
If patients has symptoms of SLE + positive for the dsDNA auto-antibody with good sensitivity and specificity
Rheumatoid factor
An antibody directed against the Fc portion of IgG of patient - not diagnostic of RA and sensitivity and specificity are low
Anti-CCP antibody (ACPA)
- More specific for RA than RF
- Can monitor the autoantibodies over time to see if it goes up or down
- ACPA + patients have more severe disease
Anti-neutrophilic cytoplasmic antibodies (ANCA)
- Test when Vasculitis is suspected
- Used in diagnosis of Granulomatosis with Polyangitis
What is vasculitis
Immune system attacking blood vessels
Cytoplasmic ANCA pattern
- Granular fluorescence of neutrophil cytoplasm
- Target antibody PR3,MPO
- result = Granulomatosis with Polyangitis
Peri-nuclear ANCA pattern
- Fluorescence of the nucleus only
- Pattern caused by PR3/MPO
Symptoms of Granulomatosis with Polyangitis
- Ulcerations in oral cavity
- Pericarditis in heart
- Conjunctivitis in eye
- Glomerulonephritis
Clinical utility of ANCA testing
+/- tests helpful in suggesting the diagnosis
- Negative ANCA assays do not exclude vasculitis as 10-50% patients will be ANCA negative
Autoimmune liver disease
- Anti-mitochondrial antibody
- Anti-smooth muscle + LKS antibodies found in autoimmune hepatitis
- detected by specific testing
Autoantibodies in type 1 diabetes
Several non-pathogenic types
- Islet cell AB, Insulin AB
- Disappear with progression of disease
Role of autoantibodies in diagnosis of type 1 diabetes
- Negative predictive value of ICA + IAA is 99%
- identify relatives at risk
