Clinical information
Diagnostic Utility:
Determination of fetal Rh(c) genotype from cell-free DNA in the plasma of pregnant women allows the Rh(c) Group of the fetus to be known in a non-invasive way, always in the context of pregnant women with a Rh(c) negative phenotype.
- In pregnant women with anti-c alloantibodies, this determination allows to identify high-risk pregnancies, in which the fetus is confirmed as Rhc positive. If, on the other hand, the fetus is Rh(c) negative, the risk of hemolytic disease due to anti-c is ruled out, and therefore monitoring is limited to the usual in a normal pregnancy.
Method:
Prior to determining the fetal Rh(c) genotype in maternal plasma, DNA extraction must be performed from a plasma aliquot separated under suitable conditions to minimize the risk of contamination.
The determination is carried out using the real-time PCR technique, using specific primers for polymorphisms associated with Rhc antigen expression, in combination with a TaqMan probe labelled with a fluorochrome. The determination also includes amplification of the SRY gene as a specific marker for the Y chromosome.
Reference Values
Possible results are: Fetus Rhc Negative / Fetus Rhc Positive.
In the case that the result is a Rhc negative female fetus, the result is reported and a new sample from the pregnant woman is requested to repeat the determination and confirm the result.
Diagnostic Algorithm:
Not applicable
Turnaround Time:
15 days
Specimen information
Sample: Total blood (sample obtained from week 16 of gestation)
Tube: EDTA K3 10 ml tube
Minimum volume: 8 ml
Precautions:
- Sample taken exclusively for this determination
- Untouched vacutainer tube
- It is important that the gestational week is indicated on the request
Stability:
- At room temperature: 2 days
- In the refrigerator: 2 days
Transport instructions: room temperature
Reasons for rejection:
- Sample arrived at the laboratory > 2 days post-extraction.
- Highly hemolyzed sample
- Sample with insufficient volume
Administrative information
BST Code: 4955
Test Description: Fetal Rh(c) genotype in maternal plasma
Synonyms: Fetal Rhc
Section: Immunohematology
BST Rate: Check the updated rates here.
Profiles:
Test 4955 is not included in any profile.
References
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Finning, K., Martin, P., Summers, J. and Daniels, G. (2007), Fetal genotyping for the K (Kell) and Rh C, c, and E blood groups on cell‐free fetal DNA in maternal plasma. Transfusion, 47: 2126-2133.