T4 - L3 Diagnosis of autoimmune diseases

Question 1

Diagnostic tests should be used to answer specific questions and/or to support a clinical
diagnosis and not as screening tools, why is this\/

Answer 1

we will get false positives

Question 2

what is sensitivity?

Answer 2

measure of how good the test is in identifying the

disease

Question 3

what is specificity?

Answer 3

measure of how good the test is at correctly defining people without the disease

Question 4

what is a true positive?

Answer 4

test is positive
disease is positive

good sensitivity

Question 5

what is a false negative?

Answer 5

test is negative
disease is positive

should retest

Question 6

what is a false positive?

Answer 6

test is positive

disease is negative

Question 7

what is a true negative?

Answer 7

test is negative

disease is negative

Question 8

what is meant by the positive predictive value?

Answer 8

The proportion of people with a positive test who have the target disorder.

Question 9

what is meant by the negative predictive value?

Answer 9

The proportion of people with a negative test who do not have the target disorder.

Question 10

what are the two types of diagnostic test?

Answer 10

non-specific:
- inflammatory markers

disease-specific:

• autoantibody testing
• HLA typing

Question 11

list some non-specific markers of systemic inflammation

Answer 11

inflammatory markers:

ESR
CRP
Ferritin
Fibrinogen 
Haptoglobin 
Albumin 
Complement

Question 12

what does the inflammatory marker ESR measure?

Answer 12

Erythrocyte sedimentation rate

• rate at which erythrocytes separate from the plasma
• higher the rate indicates inflammation somewhere in the body

Question 13

what does the inflammatory marker CRP measure?

Answer 13

• C-reactive protein

- protein made by the liver and released into the blood as a result of tissue injury (infection/inflammation)

Question 14

what does the inflammatory marker ferritin measure?

Answer 14

The ferritin concentration within the blood stream reflects the amount of iron stored in your body.

Question 15

what does the inflammatory marker haptoglobin measure?

Answer 15

• free haemoglobin in the blood
• free haemoglobin only seen when RBCs are destroyed
• When large numbers of RBCs are destroyed, haptoglobin concentrations in the blood will temporarily decrease as the consumption of haptoglobin exceeds that produced by the liver.

Question 16

what are antinuclear antibodies (ANA)?

Answer 16

Antibodies in the patient’s blood that bind to and attack the cell nucleus

NB: We can be then more specific and identify subtypes of antibody that
bind to different bits of the cell nucleus

Question 17

what does ANA testing look at?

Answer 17

identify subtypes of antibody that

bind to different bits of the cell nucleus

Question 18

what is indirect immunofluorescence?

Answer 18

Addition of an antibody (e.g. agar plate with patient serum) indirectly to detect the patient’s antibody

Question 19

what tests can you use to detect anti-dsDNA?

Answer 19

● Crithidia luciliae assay (protosoa)

● Farr assay

● ELISA

Question 20

what tests can you use to detect ENA’s?

Answer 20

immunoblots

individual ELISA

combination of antigens

Question 21

which autoantibodies are associated with SLE?

Answer 21

anti-dsDNA, Smith

Question 22

which autoantibodies are associated with rheumatoid arthritis?

Answer 22

Rheumatoid factor (RF)

Anti-CCP Antibody (ACPA) - more specific

Question 23

why is the Rheumatoid factor (RF) not diagnostic of rheumatoid arthritis?

Answer 23

• sensitivity and specificity around 70%

- can be seen in other diseases