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PPS - infections > HIV - laboratory testing > Flashcards

HIV - laboratory testing Flashcards

1
Q

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

A

Serum or plasma

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2
Q

What additive is added to carry out HIV testing?

A

Heprin

EDTA

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3
Q

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

A

Chemiluminescent magnetic immunoassay

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4
Q

How is the CMIA carried out?

A

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

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5
Q

What is the immune complex made up of?

A

Target antigen

Biotinylated antibody

Ruthenium-labelled antibody

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6
Q

What is biotinylated?

A

The process of covalently binding the vitamin biotin to a protein

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7
Q

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

A

Via interaction with biotin

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8
Q

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

A

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

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9
Q

How long does the complete assay take?

A

29 minutes

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10
Q

How many CMIA tests can be run per hour?

A

150 per hour

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11
Q

What is the overall specificity of the CMIA?

A

99.7%

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12
Q

What is the HIV antibody sensitivity of the CMIA?

A

100%

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13
Q

What does a negative CMIA result indicate?

A

Assay has 100% specificity

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

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14
Q

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

A

Test should be taken again

At 3 months post-exposure

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15
Q

What does a strong positive result CMIA result indicate?

A

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

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16
Q

What happens if a weak positive CMIA result occurs?

A

Different HIV test will be conducted

Using a different analyser

17
Q

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

A

VIDAS

18
Q

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

A

HIV-1

19
Q

What are the two sub-types of HIV infection?

A

HIV-1

HIV-2

20
Q

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

A

ImmunoComb assay

Enzyme immunoassay

21
Q

What does the ImmunoComb assay do?

A

Qualitative differential detection of antibodies to type 1 and type 2

22
Q

What sample is used for the ImmunoComb assay?

A

Serum

Plasma

23
Q

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

A

40 minutes

24
Q

What is the sensitivity of the ImmunoComb assay?

A

100%

25
Q

What is the specificity of the ImmunoComb assay?

A

99.4%

26
Q

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

A

Third test needed after positive test is concluded from two tests

27
Q

What is tested for triple check the diagnosis of HIV?

A

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

28
Q

What is the EDTA tube test used for?

A

Used to measure the HIV viral load

Need for treatment and likelihood of progressing to AIDS

29
Q

What is the colour of the EDTA test tube top?

A

Lavender/black top

30
Q

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

A

Patient needs to be treated by

  • talking about options
  • starting conversations about therapy
31
Q

How is viral load measured?

A

RNA quantitative assays

32
Q

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

A

Measure how much virus a person is carrying

33
Q

Why does the baseline serology need to be measured?

A

May have been exposed to other blood-borne viruses

Hepatitis B and C

34
Q

Which tube is used to measure baseline serology?

A

EDTA tubes

PPS - infections (8 decks)

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