HIV Serology

Question 1

What percentage of pts are diagnosed on first test?

Answer 1

49%

Question 2

What percentage of pts are diagnosed within 1-2 years after initial negative test?

Answer 2

59%

Question 3

HIV Window period length and significance

Answer 3

1. 2 weeks to 6 months

2. Represents the time it takes for a pt with HIV to seroconvert

Question 4

What tests are used to confirm HIV during the window period?

Answer 4

1. Demonstration of circulating p24 antigen

2. Presence of viral DNA/RNA

Question 5

CDC Guidelines for testing

Answer 5

Voluntary HIV screening of all pts 13-64 without written permission or counseling

Question 6

American College of Physicians Guidelines for testing

Answer 6

Universal screening up to 75 years

Question 7

USPTF guidelines for testing

Answer 7

Universal HIV screening for 15-65

Question 8

Guidelines for low-risk pts

Answer 8

One time testing at medical clinic

Question 9

Guidelines for high-risk pts, and definition of high-risk pts

Answer 9

1. Annual or more frequent testing
2. IV drug users
   Men who have sex with men
   Persons who exchange money for sex or drugs
   Sex partners of HIV infected persons, bisexual or those who use IV drugs
   Persons who have sex with partner with unknown HIV status
   Pregnant women even if screened during previous pregnancies

Question 10

CDC recommendation of testing methods: past

Answer 10

1. ELISA as a screen

2. Western blot as a confirmatory test

Question 11

CDC recommendation of testing methods: current

Answer 11

1. Combination HIV Ag and Ab tests: p24 antigen and HIV antibodies

Question 12

Combination HIV Ag and Ab Tests

Answer 12

1. Better able to identify acute/early infection compared to Ab only tests

Question 13

Rapid Ab Tests Specifications

Answer 13

1. > 99% sensitivity and specificity

2. Must be confirmed by combination Ag and Ab tests

Question 14

HIV1/HIV2 Differentiation Assay: when it is performed

Answer 14

Performed if combination test is positive

Question 15

HIV Testing algorithm

Answer 15

1. Positive Fourth generation HIV1/HIV2 immunoassay
2. HIV1/HIV2 differentiation immunoassay
   2a. Possible result: HIV 1 antibodies detected
   2b. Possible result: HIV 2 antibodies detected
   2c. Possible result: HIV 1 and HIV 2 antibodies detected
   2d. Possible result: Indeterminate HIV 1 and HIV 2 –> further testing
3. RNA test
   3a. Possible result: positive RNA test: acute HIV 1 infection
   3b. Possible result: negative RNA test: Negative for HIV 1

Question 16

Home based HIV testing

Answer 16

1. Best suited for individuals who are unlikely to seek medical care
2. OraQuick In Home HIV test
3. Home Access HIV 1 Collection Test System

Question 17

Testing for HIV RNA

Answer 17

1. Sensitivity for established HIV infection is lower than immunoassays
2. FDA approved tests only detect HIV1
3. Primarily used for screening and monitoring disease: blood donors (RED CROSS) and confirmed HIV pts

Question 18

HIV p24 AG testing

Answer 18

1. Detectable 1-2 weeks after viral transmission
2. Les expensive than HIV RNA
3. Able to identify up to 89% of infected individuals during an acute infection

Question 19

ELISA Testing

Answer 19

1. Enzyme Linked Immunoabsorbent Assay
2. Tests for antibodies to HIV
3. High sensitivity
4. Designed to detect all infected individuals, but cannot detect infection in its earliest stage

Question 20

Western Blot

Answer 20

1. Old gold standard for confirming a positive ELISA test
2. Detects presence of antibodies to HIV in pt
3. Electrophoresis that separates lab grown HIV antigens: p24, gp41, gp120/160