Core Immunology - Diagnosis of Autoimmune Diseases (10) Flashcards
Types of diagnostic tests
- Non-specific - inflammatory markers
2. Specific - autoantibody test/HLA typing
Non-specific inflammatory markers
- ESR
- CRP
- Ferritin
- Fibrinogen
- Haptoglobin
- Albumin
- Complement
ESR (erythrocyte sedimentation rate)
Blood in capillary tube, see how long takes to drop to bottom, viscosity increases during inflammation
CRP (c-reactive protein)
Liver rapidly produces and uses in an inflammatory response, activates complement system, activated by IL-6 secretion
Ferritin
Elevated
Fibrinogen
Elevated
Haptoglobin
Binds to Hb allowing it to be degraded, elevated
Albumin
Lowered
Complement
SLE antibody leads to increase immune complexes, C3 and C4 decrease
Sensitivity
Measure of how good the test is in identifiying people with the disease
Specificity
Measure of how good the test is at correctly defining people without the disease
Positive predicitive value
The proportion of people with a positive test who have target disorder
Negative predictive value
The proportion of people with a negative test who don’t have the target disorder
ANA
Extractable nuclear antigens
Detection of ANA
Detect if antibodies against nucleus, serum and fibroblast-like cells on slide, secondary antibody added, recognises IgG with fluorescent markers
ANA present in
SLE, acute episode of illness (flu/infection), more in elderly
Detection of Anti-dsDNA
Crithidia luciliae assay (protosoa), Farr assay, ELISA
Detection of ENA’s
Immunoblots, individual ELISA’s, combination of antigens
Detection of dsDNA and ENA’s
Used to work out specific target of ANA (>100 different antibodies described in SLE)
ANA screen
dsDNA, Chromatin, ribosomal protein, SS-A, SS-B, Sm, Sm/RNP, Scl-70, Jo-1, Centromere B
Multiplex assessment non-organ specific autoantibodies with novel microbead-based immunoassay
20/30 beads with internal colouring, attach bead to antigen e.g. dsDNA, use a secondary antibody - which antigen and what bead, use laser
Rheumatoid factor
Antibody (IgM, IgG, IgA) directed against Fc portion of IgG, found in RA (70%) and chronic infections (vasculitis)
Anti-CCP (ACPA)
95% specific RA, more severe and erosive disease
Cytoplasmic (c)ANCA
Granular fluorescence of neutrophil cytoplasm with nuclear sparing
(c) ANCA target antigens
PR3, Azurocidin, Lysozyme, MPO
Perinuclear (p)ANCA
Apparent fluorescence of the nucleus only
(p) ANCA target antigens
MPO, Azurocidin, B-glucuronidase, Cathepsin G, PR3
Clinical utility of ANCA testing
- Histopathology is gold standard for diagnosis
- Neg ANCA doesn’t exclude vasculitis (10-50% neg)
- Correlation between return of ANCA and disease flare is poor
- Persistence of ANCA and no clinical signs - dont need treatment
Autoimmune liver disease
- Anti-mitochondrial Ab for primary biliary sclerosis
- Anti-smooth muscle and anti-liver/kidney/microsomal (LKS) Abs for autoimmune hepatitis
How are autoimmune liver disease antibodies detected?
IF screening using rodent tissue block (oesophagus, liver and kidney) and antigen specific ELISA
Autoantibodies in Type 1 DM
- Islet cell antibodies
- Anti-GAD65/67
- Anti-insulinoma antigen 2 (IA-2)
- Insulin autoantibodies (IAAs)
- Disappear with progression of disease and total destruction of B islet cells
Diagnosis and autoantibodies of Type 1 DM
Disease conformation, identify relatives and patients at risk
