This document outlines an algorithm and provides comments for interpreting and reporting results from HIV screening tests. It describes the typical screening and confirmation testing process and provides guidance on interpreting various result patterns. It also includes questions and discussion points about challenging result scenarios and sample storage requirements. The goal is to help standardize the interpretation and reporting of HIV screening test results.

1. HIV- antenatal screening
algorithms and reporting
Judith Timms
Consultant Virologist and IDPS laboratory
advisor

2. HIV infection screening
4th or 5th generation assay
Detected Not-detected
Confirmation: second 4th
or 5th
generation
assayand HIV typing assay
HIV antibody / antigen not
detected
Both detected
Confirmed
Depending on typing result
report as HIV-1, HIV-2 or
both*
Confirmed
HIV-1 (positive)
HIV-2 (negative)
Confirmed
HIV-1 (negative)
HIV-2 (positive)
*Confirmed
HIV-1 (positive)
HIV-2 (positive)
Not detected in both
confirmatory assays
Not detected in typing assay
but detected in second
fourth or fifth generation
assay
Not detected in second 4th
or 5th generation assay but
detected in typing assay
**Indeterminate:
repeat in 2 weeks
(likelyto be false positive)
Repeat sample: serology
unchanged or screening
assayalso negative
indicates false positive
Possible early infection***
Request repeat serology
and viral load
Repeat serology unchanged (both 4th
or 5th
generation assays reactive) or
now also reactive in typing assay, and
HIV-1 RNA detected indicates HIV-1
infection confirmed
Highly unusual pattern of
results: discuss with
reference laboratory
Repeat serology unchanged (both 4th
or 5th
generation assays detected)
and HIV-1 RNA not detected:
consider early HIV-2 infection or false
positive in both 4th
or 5th
generation
assays and discuss results with
reference laboratory
Day 1 – receipt of sample in
the laboratory
Day 8 – reporting of screening
results
HIV testing algorithm and comments
HIV TESTING
ALGORITHM
*In practice HIV 1 and 2 coinfection would be incredibly rare and results should be discussed
with reference laboratory.
**Some labs may report as not detected if screening test was very close to the cut-off but there is no national consensus on this.
***Supported if one or both 4th Generation assays used gives separate results for p24 antigen and HIV antibody and the p24
antigen is detected and antibody not detected. Most HIV viral load assays are not validated for serum samples and unless
laboratory has done their own in-house validation a separate EDTA sample will be required. Original sample volume may be
inadequate for viral load testing even if validated.

3. HIV infection screening
4th or 5th generation assay
Detected Not-detected
Confirmation: second 4th
or 5th
generation
assayand HIV typing assay
HIV antibody / antigen not
detected
Both detected
Confirmed
Depending on typing result
report as HIV-1, HIV-2 or
both*
Confirmed
HIV-1 (positive)
HIV-2 (negative)
Confirmed
HIV-1 (negative)
HIV-2 (positive)
*Confirmed
HIV-1 (positive)
HIV-2 (positive)
Not detected in both
confirmatory assays
Not detected in typing assay
but detected in second
fourth or fifth generation
assay
Not detected in second 4th
or 5th generation assay but
detected in typing assay
**Indeterminate:
repeat in 2 weeks
(likelyto be false positive)
Repeat sample: serology
unchanged or screening
assayalso negative
indicates false positive
Possible early infection***
Request repeat serology
and viral load
Repeat serology unchanged (both 4th
or 5th
generation assays reactive) or
now also reactive in typing assay, and
HIV-1 RNA detected indicates HIV-1
infection confirmed
Highly unusual pattern of
results: discuss with
reference laboratory
Repeat serology unchanged (both 4th
or 5th
generation assays detected)
and HIV-1 RNA not detected:
consider early HIV-2 infection or false
positive in both 4th
or 5th
generation
assays and discuss results with
reference laboratory
Day 1 – receipt of sample in
the laboratory
Day 8 – reporting of screening
results
HIV testing algorithm and comments
HIV TESTING
ALGORITHM
*In practice HIV 1 and 2 coinfection would be incredibly rare and results should be discussed
with reference laboratory.
**Some labs may report as not detected if screening test was very close to the cut-off but there is no national consensus on this.
***Supported if one or both 4th Generation assays used gives separate results for p24 antigen and HIV antibody and the p24
antigen is detected and antibody not detected. Most HIV viral load assays are not validated for serum samples and unless
laboratory has done their own in-house validation a separate EDTA sample will be required. Original sample volume may be
inadequate for viral load testing even if validated.
√ √
√

4. HIV testing algorithm and comments
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS

5. HIV testing algorithm and comments
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS

6. HIV TESTING ALGORITHM
Greatest
concern?
HIV testing algorithm and comments

7. HIV TESTING ALGORITHM
HIV testing algorithm and comments
Greatest
concern?
Biggest problem?

8. Vast majority of screening tests will be scenario 1.
Scenario 2 – most HIV positive women will give this set of
results on their screening sample = HIV-1.
Scenario 2 – laboratories may occasionally see this = HIV 2.
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

9. INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

10. Question 1
Has anyone seen a genuine co-infection?
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

11. INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

12. Most false positive HIV results fall into this category
Question 2
Some labs may report as negative if screening test was very close to the
cut-off but there is no national consensus on this.
Is your laboratory happy to report as negative if screening test very close
to the cut-off?
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

13. INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

14. INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

15. Question 3
Neither Ag/Ab assay gives separate results for antibody and p24.
(a) Would you report like this or send away urgently for p24 testing?
(b) Would you want to report this more strongly? eg Serology suggests
acute HIV infection?
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

16. INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

17. Question 4
Would you want to ask for a viral load at this point?
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

18. INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

19. Question 5
Has anyone seen this pattern of results?
INTERPRETATIONAND CLINICALCOMMENTS FOR
REPORTING HIV SCREENING TESTS
HIV testing algorithm and comments

20. SOMETHING SLIGHTLY DIFFERENT
Sample storage: draft comment
When the screening tests are complete an aliquot (a suggested minimum
volume of 300 microliters) from the screening specimen must be stored
frozen at a minimum temperature of -20 OC for at least 2 years.
HIV testing algorithm and comments

21. SOMETHING SLIGHTLY DIFFERENT
Sample storage: draft comment
When the screening tests are complete an aliquot (a suggested minimum
volume of 300 microliters) from the screening specimen must be stored
frozen at a minimum temperature of -20 OC for at least 2 years.
Is the wording correct here?
HIV testing algorithm and comments

22. SOMETHING SLIGHTLY DIFFERENT
Sample storage: draft comment
When the screening tests are complete an aliquot (a suggested minimum
volume of 300 microliters) from the screening specimen must be stored
frozen at a minimum temperature of -20 OC for at least 2 years.
In cases where there is insufficient volume to store an aliquot of the
screening specimen then a local process should be in place to document,
monitor and manage this, for example by requesting a second sample
and informing the women of the reason.
Laboratories should consider reporting the proportion of samples where it
is not possible to store an aliquot of the screening specimen to maternity
services.
HIV testing algorithm and comments

23. SOMETHING SLIGHTLY DIFFERENT
Sample storage: draft comment
When the screening tests are complete an aliquot (a suggested minimum
volume of 300 microliters) from the screening specimen must be stored
frozen at a minimum temperature of -20 OC for at least 2 years.
In cases where there is insufficient volume to store an aliquot of the
screening specimen then a local process should be in place to document,
monitor and manage this, for example by requesting a second sample
and informing the women of the reason.
Laboratories should consider reporting the proportion of samples where it
is not possible to store an aliquot of the screening specimen to maternity
services.
How feasible are these last 2 statements?
HIV testing algorithm and comments