32nd Page

Question 1

What is the hallmark feature of AIDS?

Answer 1

CD4 lymphopenia

Question 2

How often should CD4 T cell enumeration be determined?

Answer 2

Every 3-6 months

Question 3

What are the methods for CD4 T cell enumeration? (MEEI)

Answer 3

Manual bead assay
Enzyme immunoassay
ELISA
Immunophenotyping (by Flow cytometry)

Question 4

What is the specimen preparation for CD4 T cell enumeration? (IRB)

Answer 4

Incubated with a panel of fluorescent-labeled monoclonal Ab

RBC lysis

Fixation of WBCs with paraformaldehyde

Question 5

How is the percentage of CD4 T cells reported?

Answer 5

%CD4 = (#CD4 lymph x 100) / Total # lymph

Question 6

What is the normal ratio of CD4+:CD8+ cells?

Answer 6

2:1

Question 7

What is the CD4+:CD8+ cell ratio in HIV?

Answer 7

1:2 / 0.5:1

Question 8

What CD4 cell count indicates AIDS?

Answer 8

<200 cells/µL

Question 9

What is the standard screening method for detecting HIV antibodies?

Answer 9

ELISA

Question 10

What antibodies are detected by ELISA?

Answer 10

Antibodies against p24, gp120, gp160, and gp41

Question 11

1st generation ELISA

Answer 11

detects HIV-1 only

Genetically engineered (purified Ag from HIV-1 and HIV-2)

Question 12

3rd generation ELISA

Answer 12

Sandwich technique

Question 13

4th generation ELISA

Answer 13

EIA or IFA - detects HIV-1, HIV-2, p24 Ag

Question 14

2nd generation ELISA

Answer 14

genetically engineered (purified Ag from HIV-1 and HIV-2

Question 15

What must be done with positive ELISA?

Answer 15

Duplicate samples must be retested from the original specimen

Question 16

What is used to confirm ELISA results?

Answer 16

Western Blot, 2 out of 3 reactive

Question 17

What is the Western Blot?

Answer 17

A confirmatory test used in immunology and serology for HIV

Question 18

What is the first step in the Western Blot procedure?

Answer 18

React patient serum with antigen in a nitrocellulose strip.

Question 19

What is done after reacting the serum with antigen?

Answer 19

Wash to remove unbound antibodies.

Question 20

What is added after washing in the Western Blot procedure?

Answer 20

Add antihuman-Ig with enzyme label.

Question 21

What is the purpose of adding substrate in the Western Blot?

Answer 21

To detect bound conjugate, resulting in colored bands.

Question 22

Which proteins appear first in the Western Blot?

Answer 22

p24 and p55.

Question 23

What indicates a negative result in Western Blot interpretation?

Answer 23

No colored bands.

Question 24

What indicates a positive result in Western Blot interpretation?

Answer 24

At least 2 of the following: P24, gp41, gp120/gp160.

At least 3 of the following: p24, p55, gp41, gp120/gp160.

Question 25

Indeterminate results are those samples that produce bands but not enough to be positive, may be due to the following:

Answer 25

1. prior blood transfusions, even with non-HIV-1 infected blood
2. prior or current infection with syphilis
3. prior or current infection with malaria
4. autoimmune diseases
5. infection with other human retroviruses
6. second or subsequent pregnancies in women
   * run an alternate HIV confirmatory assay

Question 26

What should be done with indeterminate results?

Answer 26

Repeat the test with the same or a fresh specimen.

Question 27

samples that produce bands but not enough to be positive

Answer 27

Indeterminate

Question 28

remain throughout all disease stages in western blot

Answer 28

gp31, gp41, gp120, gp160

Question 29

procedure in western blot

Answer 29

1) Px serum → react with Ag in nitrocellulose strip
2) wash (remove unbound Ab)
3) Add antihuman-Ig with enzyme label.
4) Wash
5) Bound conjugate is detected after addition of substrate (colored bands)

Question 30

absolute CD4 = WBC count x % lymph x % CD4 T cells

Answer 30

NV: 500-1300 uL (<200/uL to AIDS)