HIV - laboratory testing

Question 1

What sample is needed to carry out lab testing for HIV?

Answer 1

Serum or plasma

Question 2

What additive is added to carry out HIV testing?

Answer 2

Heprin

EDTA

Question 3

What test is done in the lab to test for HIV infection?

Answer 3

Chemiluminescent magnetic immunoassay

Question 4

How is the CMIA carried out?

Answer 4

An immune complex is formed

Streptavidin-coated magnetic microparticles are added that bind to the complex

Complexes bind to the magentic surfaces on the electrode

Application of voltage generates electrochemiluminescence in the ruthenium complex

Question 5

What is the immune complex made up of?

Answer 5

Target antigen

Biotinylated antibody

Ruthenium-labelled antibody

Question 6

What is biotinylated?

Answer 6

The process of covalently binding the vitamin biotin to a protein

Question 7

How do the streptavidin-coated magnetic microparticles bind to the immune complex?

Answer 7

Via interaction with biotin

Question 8

How do you measure the amount of target antigen present in the sample?

Answer 8

Light formed when voltage is applied to the complex via electrochemiluminescence

Measured by a photomultiplier

Used to calculate the amount of target antigen present in the sample

Question 9

How long does the complete assay take?

Answer 9

29 minutes

Question 10

How many CMIA tests can be run per hour?

Answer 10

150 per hour

Question 11

What is the overall specificity of the CMIA?

Answer 11

99.7%

Question 12

What is the HIV antibody sensitivity of the CMIA?

Answer 12

100%

Question 13

What does a negative CMIA result indicate?

Answer 13

Assay has 100% specificity

A negative result where there has been no exposure in the last three months should rule out HIV infection

Question 14

What if a patient has a negative CMIA but has been exposed to HIV in the last 3 months?

Answer 14

Test should be taken again

At 3 months post-exposure

Question 15

What does a strong positive result CMIA result indicate?

Answer 15

Same test should be repeated

Additionally immunocomb test should be carried out to identify which of the two major HIV types the patient is infected with

Question 16

What happens if a weak positive CMIA result occurs?

Answer 16

Different HIV test will be conducted

Using a different analyser

Question 17

What is an example of an alternative HIV test that can be conducted?

Answer 17

VIDAS

Question 18

What is the most common sub-type of HIV infection?

Answer 18

HIV-1

Question 19

What are the two sub-types of HIV infection?

Answer 19

HIV-1

HIV-2

Question 20

What is the commonest test performed to differentiate between the two sub-types HIV-1 and HIV-2?

Answer 20

ImmunoComb assay

Enzyme immunoassay

Question 21

What does the ImmunoComb assay do?

Answer 21

Qualitative differential detection of antibodies to type 1 and type 2

Question 22

What sample is used for the ImmunoComb assay?

Answer 22

Serum

Plasma

Question 23

How much time does an ImmunoComb assay take to produce results?

Answer 23

40 minutes

Question 24

What is the sensitivity of the ImmunoComb assay?

Answer 24

100%

Question 25

What is the specificity of the ImmunoComb assay?

Answer 25

99.4%

Question 26

What happens once two tests have concluded the presence of HIV?

Answer 26

Third test needed after positive test is concluded from two tests

Question 27

What is tested for triple check the diagnosis of HIV?

Answer 27

Two serum samples in gold-top SST tubes One sample is re-tested to confirm the result and patient identity The other sample will be tested for baseline serology

Question 28

What is the EDTA tube test used for?

Answer 28

Used to measure the HIV viral load Need for treatment and likelihood of progressing to AIDS

Question 29

What is the colour of the EDTA test tube top?

Answer 29

Lavender/black top

Question 30

What happens whilst the patient is being tested for HIV for the third time?

Answer 30

Patient needs to be treated by - talking about options - starting conversations about therapy

Question 31

How is viral load measured?

Answer 31

RNA quantitative assays

Question 32

How do quantitative assays differ from HIV diagnostic ELISA or POCT?

Answer 32

Measure how much virus a person is carrying

Question 33

Why does the baseline serology need to be measured?

Answer 33

May have been exposed to other blood-borne viruses Hepatitis B and C

Question 34

Which tube is used to measure baseline serology?

Answer 34

EDTA tubes