Diagnosis of autoimmune diseases

Question 1

What is the sensitivity of a test

Answer 1

How good the test is for identifying people with the disease

Question 2

Specificity

Answer 2

Measure of how good the test is at defining people without disease

Question 3

Positive predictive value

Answer 3

Proportion of positive tests with disorder

Question 4

Negative predictive value

Answer 4

Proportion of negatives without disorder

Question 5

Types of diagnostic test

Answer 5

Non-specific - inflammatory markers

Disease specific - Autoantibody testing, HLA typing

Question 6

Non-specific markers of systemic inflammation

Answer 6

Inflammatory markers:

ESR, CRP, albumin, complement etc

Question 7

What are Antinuclear antibodies

Answer 7

• Antibodies produced by patient in blood that binds to cell nucleus

Question 8

How does the ANA test work

Answer 8

• 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

Question 9

Detection of dsDNA and ANA’s techniques

Answer 9

Anti-dsDNA: Farr assay, ELISA, protozoa

ANA’s: Immunoblots

Question 10

SLE diagnosis with autoantibody

Answer 10

If patients has symptoms of SLE + positive for the dsDNA auto-antibody with good sensitivity and specificity

Question 11

Rheumatoid factor

Answer 11

An antibody directed against the Fc portion of IgG of patient - not diagnostic of RA and sensitivity and specificity are low

Question 12

Anti-CCP antibody (ACPA)

Answer 12

• 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

Question 13

Anti-neutrophilic cytoplasmic antibodies (ANCA)

Answer 13

• Test when Vasculitis is suspected

- Used in diagnosis of Granulomatosis with Polyangitis

Question 14

What is vasculitis

Answer 14

Immune system attacking blood vessels

Question 15

Cytoplasmic ANCA pattern

Answer 15

• Granular fluorescence of neutrophil cytoplasm
• Target antibody PR3,MPO
• • result = Granulomatosis with Polyangitis

Question 16

Peri-nuclear ANCA pattern

Answer 16

• Fluorescence of the nucleus only

- Pattern caused by PR3/MPO

Question 17

Symptoms of Granulomatosis with Polyangitis

Answer 17

• Ulcerations in oral cavity
• Pericarditis in heart
• Conjunctivitis in eye
• Glomerulonephritis

Question 18

Clinical utility of ANCA testing

Answer 18

+/- tests helpful in suggesting the diagnosis

- Negative ANCA assays do not exclude vasculitis as 10-50% patients will be ANCA negative

Question 19

Autoimmune liver disease

Answer 19

• Anti-mitochondrial antibody
• Anti-smooth muscle + LKS antibodies found in autoimmune hepatitis
• detected by specific testing

Question 20

Autoantibodies in type 1 diabetes

Answer 20

Several non-pathogenic types

• Islet cell AB, Insulin AB
• Disappear with progression of disease

Question 21

Role of autoantibodies in diagnosis of type 1 diabetes

Answer 21

• Negative predictive value of ICA + IAA is 99%

- identify relatives at risk