HIV Ab/Ag (Human Immunodeficiency Virus I/II Serology)

Useful For

Screening persons at risk for sexually transmitted and bloodborne infections, including HIV-1 and HIV-2.


Testing Algorithm

Reporting Name Available separately Always performed
HIV Screen N/A N/A
HIV-1/2 Antigen/antibody combo assay NO YES
HIV-1 WB (HIV-1 Western Blot) NO NO
HIV-2 WB (HIV-2 Western Blot) NO NO

Serum/plasma screened for HIV p24 antigen and HIV 1/2 antibodies employing HIV antigen/antibody combo assay. Reactive specimens are confirmed by HIV 1 specific Western blot (ie: immunoblot, ImB).


Indications for Testing

Adults and adolescents

  • Routine serological workup of clients/patients not previously tested for HIV
  • Routine serological workup of clients/patients in at risk populations previously tested (≥ 1 year) negative
  • Routine serological workup of clients/patients presenting with a sexually transmitted infection (STI)
  • Mononucleosis-like illness (MLI) in at risk populations.


Patients may seek medical attention for issues unrelated to sexual health, but they may be at risk for STIs and benefit from screening and interventions to address identified risk factors.


Population groups in Canada considered at increased risk of HIV infection include youth, aboriginal peoples, woman, peoples from endemic countries, prison inmates, injecting drug users, men who have sex with men.


Prenatal care

  • HIV testing forms part of routine prenatal infectious disease screen.
  • Woman who test negative early in pregnancy but who continue high-risk behaviours should be offered repeat testing each trimester and at term.
  • Woman not tested earlier in pregnancy should be offered testing as soon as they present for care.


Pediatric and Neonatal

  • For infants born to mothers with unknown HIV status, HIV antibody testing of the mother and/or infant is recommended as soon as possible after birth. If the HIV antibody assay is positive an HIV viral load PCR should be obtained from the infant.
  • For infants born to HIV-positive mothers, and to diagnose HIV in infants <18 months, an HIV viral load PCR should be performed within the first 14–21 days of life, at 1–2 months, and at 4–6 months of age.
  • For infants born to HIV-positive mothers, HIV antibody testing should be performed on the infant at 12-18 months of age to confirm the absence of HIV infection and to document loss of maternal anti-HIV antibodies.


In children ≥18 months of age, HIV antibody assays alone can be used for diagnosis.

Method Name

Chemiluminescent microparticle immunoassay (CMIA)


Reporting Name






Human Immunodeficiency Virus


Mononucleosis like illness


Sexually transmitted infection / disease



Specimen Required

Serology: Suitable specimens are individual samples (human sera or EDTA/heparinized/citrated plasma) obtained by standard laboratory techniques.


Specimen Minimum Volume



Transport Temperature

Specimen Room temperature Refrigerated Frozen
Serum/plasma YES* YES** YES***

*The samples should not be stored for more than 3 days at room temperature.

**The samples should be stored for not more than 14 days at 2-8°C.

***For longer delay, freeze at -70°C and transport on dry ice.


Reject Due To

Specimens other than Serum or Plasma
Anticoagulants OK
Lipemia OK
Icteric OK
Cadaveric REJECT*

* Contact the laboratory for cadaveric specimen instructions.


Useful For

Screening persons at risk for sexually transmitted and bloodborne infections, including HIV-1 and HIV-2.


Clinical Information

Early diagnosis during the critical stages of acute HIV infection represents a tremendous opportunity for treatment and prevention interventions.


Soon after localized infection is established (eclipse phase) virus dissemination occurs. Due to dissemination of virus some individuals, but not all, will develop signs and symptoms of acute retroviral syndrome, which can include fever, rash, night sweets, severe fatigue, headache, diarrhea, pharyngitis, arthralgia, and myalgias. The onset of symptoms (due to chemokine storm) typically occurs around 2 weeks after HIV acquisition, coincident with the peak of viremia. The first marker (viral RNA) appears around this time (detectable only by ultrasensitive PCR). Seven days later viral p24 antigen becomes detectable. After another 5 days anti-HIV-1 antibodies (mostly IgM) reach levels detectable by antibody screening tests. A few days (3) later the Western Blot confirmatory tests typically converts from negative to indeterminate and can stay indeterminate for another 7 days – 1 month before converting to a clear positive.


Reference Values




HIV Ag/Ab HIV WB Interpretation Comments
Non-reactive N/A Negative If high risk and acute infection is suspected retest in 1 – 2 weeks.
Reactive Non-reactive Negative If high risk or acute infection is suspected retest in 1 – 2 weeks.
Reactive Indeterminate Indeterminate Repeat testing to detect seroconversion
Reactive Reactive Positive Confirmed case*

*If a patient is found to be HIV-positive, a repeat blood collection and testing should be ordered to validate results.


HIV antibody testing cannot establish HIV infection in infants <18 months old due to persistent maternal anti-HIV antibodies in HIV-positive mothers. Confirmation of HIV infection in those <18 months old should be based on two positive virologic tests (HIV RNA/DNA PCR) obtained from separate blood samples. Definitive exclusion of HIV infection (in the absence of breastfeeding) should be based on at least two negative virologic tests (one at >1 month and one at >4 months of age).



Clinical Reference

Cohen, M.S., Gay, C.L., Busch, P.B., and Hecht, F.M. 2010. The detection of acute HIV infection. J Infect Dis. 2002(S2):S270-S277.


Burdge, D.R., Money, D.M., Forbes, J.C., et al. 2003. Canadian consensus guidelines for the management of pregnant HIV-positive woman and their offspring. CMAJ. 2003;168(13):1683-8.



Status Days Analytic Time Maximum Laboratory Time Specimen Retention
Routine Daily (Western Blot, Monday) 7h 72 h 1 month


Method Description

Chemiluminescent microparticle immunoassay (CMIA) for the simultaneous qualitative detection of HIV p24 antigen and antibodies to human immunodeficiencey virus type 1 and/or type 2 (HIV-1/HIV-2) in human serum or plasma.


Performing Laboratory Location

Newfoundland & Labrador Public Health Laboratory

St. John’s


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