Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
D negative women who carry a D positive fetus may produce antibodies to the fetal D antigens after a fetomaternal haemorrhage or birth. Such antibodies may cross the placenta in future pregnancies and can cause haemolytic disease if the fetus is D positive. Traditionally, routine antenatal prophylaxis has been offered to all D negative women to reduce the incidence of haemolytic disease, and additionally women are offered anti-D if they have any sensitising events. Approximately 40% of D negative mothers will carry a D negative baby and hence are not a risk of alloimmunisation and HDFN caused by anti-D antibodies. These women do not require RAADP and as such are exposed to a product of human origin unnecessarily. NHSBT IBGRL have developed a non-invasive molecular technique, which uses a maternal sample to detect free fetal DNA (FFDNA) in maternal plasma. Testing is possible from 11 weeks gestation. D negative women who accept the offer of FFDNA testing will have an additional blood test, ideally at about 16 weeks of pregnancy which will identify the fetal D status. Those women who are carrying a D negative baby could avoid unnecessary treatment with anti-D immunoglobulin. Those women who are carrying a D positive baby can make an informed choice about whether to have treatment with anti-D immunoglobulin. Women must have immune anti-D antibodies for this test.
Specimen container paediatric:
N/A
Specimen container adult:
Minimum of 6mL EDTA
Minimum volume paediatric:
N/A
Minimum volume adult:
6mL
Special requirements:
Specific NHSBT FFDNA Form (5197/2.1) must be completed. EDD must be present on request form.
Sample must be HANDWRITTEN and be sent with a signed request form.
Sample stability:
Short term storage: 24 hours at room temperature. Long term storage: 7 days at 4-6°C
Transport requirements:
Sample should be transported to Laboratory Medicine Reception via GP courier, hospital air-tube system or hand delivered to maintain storage conditions. Samples must not be subjected to extreme hot or cold conditions prior to testing.
Interpretation:
If maternal D status is D NEGATIVE and the Fetal RHD typing predicts that this fetus is D POSITIVE, RAADP (anti-D prophylaxis) is indicated unless maternal allo anti-D is present.
If maternal D status is D NEGATIVE and the Fetal RHD typing predicts that this fetus is D NEGATIVE, RAADP (anti-D prophylaxis) IS NOT required in this pregnancy
If the maternal D status is D NEGATIVE and the Fetal RHD typing is INCONCLUSIVE, the pregnancy is managed as if the fetus is D POSITIVE and anti-D prophylaxis is indicated unless maternal allo anti-D is present.
Other info:
This test is referred to NHSBT by the Transfusion laboratory.