Fetal Rhesus D screening test | Genomic Diagnostics

Test description

Fetal Rhesus D screening can determine the RhD status of the fetus in RhD-negative mothers who do not have anti-D alloantibodies. If the fetus is also RhD negative, prophylactic anti-D immunoglobulin is not required—avoiding unnecessary treatment that is otherwise routinely given throughout pregnancy.

Test information

Test name

Fetal Rhesus D Screening

Clinical indication

To determine fetal RhD status where the mother is RhD negative and not alloimmunised.

Gene(s)

RHD

Method

Real-time PCR

Turn around time

1 – 2 weeks

Medicare eligibility

73420, conditions apply

Price

If not MBS eligible, please contact 1800 822 999 for details

Test request form

Dedicated Fetal RhD Screening test form

Sample type

Blood

Collection type

10mL Streck tube

Special instructions

Test is recommended to be performed after 18 weeks gestation but can be performed from 11 weeks. A re-test will be required if Fetal RhD result is negative before 18 weeks.

FAQ

Why should pregnant women have Fetal Rh testing?

This screening test will help doctors decide if a woman requires prophylactic anti-D immunoglobulin during her pregnancy. Fetal RhD (Rhesus D) Screening as part of routine pregnancy care is supported by the Australian National Blood Authority and guidelines are available at www.blood.gov.au.

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Who is not eligible for this test?

This test is not available to women who are RhD positive, women with known RhD variants (including weak or partial RhD), and/or have a positive antibody screen due to immune anti-D. Women who are alloimmunised against other significant antigens should be discussed with a haematologist as Lifeblood’s NIPA will be more suitable. Women with twin or multiple pregnancies are also not eligible.

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When can testing be performed?

This test is recommended from 18 weeks’ gestation but can be performed from 11 weeks. Due to the nature of testing, all patients with negative results before 18 weeks should have a re-test for confirmatory purpose.

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What do the results look like?

This screening genetic test will provide one of the following results:

(1) Predicted fetal phenotype – RhD Positive

(2) Predicted fetal phenotype – RhD Negative

(3) Provisional Result: Predicted fetal RhD negative phenotype with recommendation to re-test

(4) No results available for RHD gene sequence testing

Why is re-testing required for negative results before 18 weeks’ gestation?

This Therapeutic Goods Administration (TGA) registered test recommends that all negative results for samples collected before 18 weeks’ gestation have a second test performed for confirmation. This test is dependent on the quantity of DNA from the placenta that is circulating in the woman’s peripheral blood. Therefore, repeat testing later in pregnancy when the fetus (and placenta) are more mature will increase its accuracy.

Please note that positive results before 18 weeks’ gestation do not require a second test.

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Why does the report say “No results available”?

This happens when the test needs to be repeated because of the age of gestation OR when a variant RhD has been identified. This is a genetic screening test and is different to serological blood grouping performed in the transfusion laboratory. The results should be discussed with the pathologist in charge of the transfusion laboratory or with a pathologist at Genomic Diagnostics.

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When should anti-D immunoglobulin be administered?

Recommendations by the National Blood Authority on the use of anti-D immunoglobulin (Ig) are available online (www.blood.gov.au). These guidelines include the use of anti-D Ig when the Rhesus D Screen results are not available.

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Can women who have a predicted fetal RhD negative phenotype still have anti-D immunoglobulin?

Yes – the decision to have RhD immunoglobulin is a clinical decision. Further information is available from the National Blood Authority guidelines (www.blood.gov.au) and ANZSBT Guidance for RHD NIPT for fetal RHD blood group prediction in pregnancy (https://anzsbt.org.au).

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Is this test the same as Lifeblood’s Non-Invasive Prenatal Analysis (NIPA) for Clinically Significant Fetal Antigens?

No – Genomic Diagnostics’ RHD (Rhesus D) Fetal Screen is not the same as Lifeblood’s Non-Invasive Prenatal Analysis (NIPA) for Clinically Significant Fetal Antigens. Samples for Lifeblood’s NIPA test should be sent directly to Lifeblood as they are collected in EDTA and need to be processed within 72hours of collection. Please contact Lifeblood’s Red Cell Reference Laboratory on +61 7 3838 9493 for any queries.

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What happens when there is discordance between the Fetal RhD (Rhesus D) Screen result and the baby’s cord blood grouping?

This is a test is registered with the Therapeutic Goods Administration (TGA) with a specificity of >96.87% and a sensitivity of 100% as reported by the manufacturer. However, because it is a screening test, confirmation testing on baby cord blood is recommended. Any discordant results should be discussed by the obstetrician with a haematologist. Anti-D immunoglobulin needs to be administered as per current guidelines (www.blood.gov.au) and the discordant case reported to Genomic Diagnostics (info@genomicdiagnostics.com.au).

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Resources

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Fetal Rhesus D screening pathology request form

Clinicians

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Fetal Rhesus D Screening Clinician Flyer

Clinicians