RhD GENOTYPING
DNA ANALYSIS

RhD hemolytic disease results from transplacental passage of maternal antibodies against RhD antigens on fetal red blood cells. While administration of immune globulin to RhD-negative pregnant women has reduced the incidence of this disease, this prevention strategy is not effective for all patients. Information about fetal RhD genotype is useful for appropriate obstetric management of RhD-negative patients. Molecular genotyping offers the advantages of obtaining early information as well as avoidance of fetal blood sampling. Two homologous genes at the RhD locus on chromosome 1p36 encode the RhD antigen (the RhD gene) and the different RhC, Rhc, RhE and Rhe antigens (the RhCE gene). The genetic basis of the RhD blood type is the presence (RhD positive) or absence (RhD negative) of the RhD gene. Approximately 15% of Caucasians are RhD negative. For those RhD positive individuals, approximately 55% are heterozygous (RhD positive/RhD negative) and the remaining 45% are homozygous.

Reasons for Referral:

Current pregnancy in an RhD-negative woman with no prior history of hemolytic disease but with elevated anti-RhD antibody titers.
Previous pregnancy complicated by RhD hemolytic disease and unknown or heterozygous RhD positive blood type in the father of the current pregnancy.
RhD negative pregnant patients undergoing amniocentesis for other indications.

Testing Methodology:

PCR amplification of the RhD gene specific sequence with co-amplification of the RhCE sequence as an internal control to determine the presence or absence of RhD.

Specimen Requirements:

Direct fetal specimen: amniotic fluid, 10 cc in a sterile container.
Both parental bloods (14 ml. in EDTA tube) must accompany the fetal sample. Cultured cells (2 T-25 flasks) are required for confirmatory analysis and as a back-up. Requisition form as well as serologic typing results for both parents must accompany specimens. For information about prenatal testing, contact our laboratory.

Turnaround Time:

3 weeks

CPT Codes and Prices:

83900, 83901x2, 83894x2, 83890, 83912

Shipping Information

Forms:

>> DNA Requisition
>> Prenatal Requisition

Test Codes:

Index: 6052
Prenatal: 6111