Prenatal – Serology

Testing Indications

Prenatal screening for HIV, syphilis, rubella and hepatitis B surface antigen [HBsAg]

Specimen Collection and Handling

Specimen Requirements

Test Requested Required Requisition(s) Specimen Type Minimum Volume Collection Kit

HBsAg

Rubella

Syphilis

HIV

 

(Check box[es]on requisition)

Serum

HBsAg 2.0mL

Rubella 1.0mL

Syphilis 2.0mL

HIV 2.0mL

Blood, clotted – vacutainer tubes (SST)

Submission and Collection Notes

1

One FULL red top or serum separator tube (SST) is sufficient for all tests.

2

Do NOT submit glass tubes.

Limitations

Haemolysed, icteric, lipemic or microbially contaminated sera is not recommended for testing. Specimens more than 6 days post collection will not be tested.

Preparation Prior to Transport

Label the specimen container with the patient’s full name, date of collection and one other unique identifier such as the patient’s date of birth or Health Card Number. Failure to provide this information may result in rejection or testing delay.

Centrifuge if using SST. Place specimen in biohazard bag and seal. Specimens should be stored at 2-8°C following collection.

Requisitions and Kit Ordering

Test Frequency and Turnaround Time (TAT)

Rubella – Serology testing is performed daily Monday to Friday. Turnaround time is up to 5 days from receipt by PHO laboratory.

Syphilis – Serology screen testing is performed daily Monday to Friday. Syphilis Confirmatory testing is performed daily Monday to Friday. Turnaround time is up to 3 days from receipt by PHO laboratory for non-reactive samples and up to 6 days for reactive samples.

HIV and Hepatitis B – Serology testing is performed daily Monday to Friday.

Turnaround time is up to 3 days from receipt by PHO laboratory for non-reactive samples and up to 6 days for reactive samples.

STAT and Critical Samples Testing

Hepatitis B Surface Antigen (HBsAg): Pregnant in labor with no prenatal work up and high risk for Hepatitis B

HIV: Pregnant in labor with no prenatal work up and high risk for HIV

Reporting

Results are reported to the ordering physician or health care provider as indicated on the requisition.

Specimens that are positive for syphilis, HIV, and/or Hepatitis B surface antigen (HBsAg) are reported to the Medical Officer of Health as per Health Protection and Promotion Act.

Test Methods

Rubella

Specimens for Rubella IgG (Immune status) are tested by a chemiluminescent microparticle immunoassay (CMIA) for the qualitative detection of human IgG antibody to Rubella virus.

Syphilis

Specimens for syphilis screening are tested by CMIA (Chemiluminescent Microparticle Immunoassay). The CMIA test detects both IgG and IgM antibodies to Treponema pallidum. 

If the CMIA is reactive - confirmatory testing is performed by both:

  • Rapid Plasma Reagin (RPR) and
  • Treponema pallidum Particulate Agglutination assay (TPPA)

RPR is a non-Treponemal Flocculation Test that detects antibodies to cardiolipin-lecithin- cholesterol. The RPR titer decreases with treatment and/or time, and is most useful for assessing acute disease, monitoring treatment and identifying reinfection.

TPPA is a qualitative gelatin particle agglutination assay that is used for the detection and confirmation of Treponema pallidum antibodies (IgG and IgM) as an aid in the diagnosis of syphilis. 

HIV

Specimens are screened for HIV by a chemiluminescent microparticle immunoassay (CMIA).The HIV Ag/Ab Combo Assay is used for the simultaneous qualitative detection of HIV p24Ag and antibodies to Human immunodeficiency virus type 1 and/or type 2 (HIV-1/HIV-2) in human serum.

If the CMIA screening test is negative, the specimen is reported as “HIV1/2 Ag/Ab Combo Screen Non-Reactive” and the report is finalized.

If the CMIA test is positive or indeterminate, the specimen is tested using the Geenius TM HIV1/2 Differential assay.

The Geenius TM HIV1/2 Differential assay is an immunochromatographic test for the confirmation and differentiation of antibodies to HIV Type 1 (HIV-1, Group M and O) and Type 2 (HIV-2) in serum or plasma samples. 

CMIA positive samples that are confirmed positive by the Geenius TM HIV1/2 Differential assay are reported as either “Positive for HIV 1” or “Positive for HIV 2 antibody” depending on the antibodies detected.

CMIA positive samples that are Negative or Indeterminate by Geenius TM HIV1/2 Differential assay are screened for P24 Ag using the VIDAS HIV P24 ll assay system. It is an automated quantitative test for the detection of HIV type 1 p24 antigen in human serum or plasma using the ELFA technique (Enzyme Linked Fluorescent Assay). Samples that are positive for P24 Ag are then confirmed using the VIDAS HIV P24 ll Confirmatory Assay.  Samples that confirm positive for P24 Ag are reported as confirmed reactive with a final interpretation of “Evidence of HIV 1 infection prior to seroconversion”.

CMIA positive samples that test Negative or indeterminate on the Geenius TM HIV1/2 Differential assay and the P24 Ag assay will be reported as inconclusive for HIV. Patients whose specimen is reported as inconclusive should have a follow up specimen submitted for repeat testing at least 4 weeks after collection of first specimen

Hepatitis B Surface Antigen (HBsAg)

Hepatitis B Prenatal specimens are tested for HBsAg by a chemiluminescent microparticle immunoassay (CMIA) for the qualitative detection of human Hepatitis B surface antigen

If HBsAg is reactive, further testing for Anti-HBc (Total) is performed.

If HBsAg is reactive, but the anti-HBc (total) is non-reactive then the specimen is tested by a HBsAg confirmatory test.

If the HBsAg and anti-HBc (total) are both reactive and the patient has acute symptoms indicated on the requisition, then the specimen will have the following tests performed: HBeAg, anti-HBe and anti-HBc IgM.

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Contact Laboratory Customer Service

Laboratory Services

customerservicecentre@oahpp.ca

Updated 22 Oct 2019