Download and Read the Sandler et al. Study

Human blood types fall into four major types: A, B, AB and O. This information was discovered in the early 20th century and make blood transfusions safer. The second most important blood group—Rh —was discovered in 1939.

Since the discovery of the Rh type, it has become routine practice to perform serologic testing to determine whether an expectant mother carries the Rh antigen, D, on her red blood cells (Rh positive) or does not have the antigen (Rh negative).

The Rh-positive (D) blood type is much more common than Rh-negative (D), and complications can arise during pregnancy when the Rh type of the mother does not match her fetus. Specifically, an Rh-negative mother can become sensitized to the Rh-positive fetal red blood cells and produce Rh(D) antibodies that pass through the placenta to the Rh-positive fetus, potentially causing hemolytic disease of the fetus and newborn (HDFN).

Hemolytic disease is characterized by destruction of fetal red blood cells, which can be life-threatening. Antepartum and postpartum Rh immune globulin (RhIG) are used to prevent maternal sensitization and this disease.

RhD blood typing is relatively straightforward in approximately 94% of patients, identifying those who require treatment with RhIG to prevent sensitization. However, in 2 to 6% of patients, depending on their ethnic background, the Rh blood type may vary depending on the testing performed and may be weakly positive or discordant with a previous type, bringing into question the Rh (D) type.

What Is the Weak Rh (D) type?

Though there have been many advancements in blood typing, there are some patients who can type as both Rh positive and Rh negative, depending on the test method.

While this inconsistency is often attributed to differences in test methods, it arises because of genetic differences in individuals at the RHD gene level that affect the levels of the D antigen expressed on the RBCs. These often present as weak and variable RhD blood typing due to inheritance of reduced quantities of RhD protein on the cell surface that may not be detected or type weak at initial testing. These genetic differences in Rh blood types were not previously able to be tested.

Though the conservative practice is to treat all obstetrical patients with a weak or variable Rh (D) blood type as Rh negative, RHD genotyping can identify those individuals who may be safely treated as Rh positive and those who should be treated as Rh negative as a precaution.

RHD genotyping is used to determine a patient’s “true” Rh blood group status and inform decisions regarding blood transfusion and RhIG administration for pregnant women.

What Are the Benefits of RHD Genotyping?

There are several benefits to incorporating RHD genotyping into your practice and patient management strategies. These include improved accuracy in RhD typing, preventing the excess use of RhIG—a human blood product which is a limited resource—and reducing expenses by eliminating unnecessary RhIG and post-delivery re-typing of the mother and typing of the neonate.

1. Improved Efficiency in RhD typing

Preventing sensitization in women who are Rh negative or have a weak or uncertain Rh type is to treat them with RhIG. This approach errs on the side of caution.

RHD genotyping, on the other hand, can provide certain and accurate genetic information, so the laboratory and health provider can act on what is known rather than on what is uncertain. Women who have the most common weak D types 1, 2 or 3 will be identified and the practitioner can confidently treat them as Rh-positive with no need for RhIG treatment.  Women who have other genetic variations in their RHD genes may be better cared for with RhIG treatment.

2. Preventing the unnecessary use of RhIG

Women who are Rh-negative but carrying a Rh-positive fetus are at high risk for complications in the next pregnancy. As a result, expectant mothers in this group are given antepartum and postpartum RhIG.

However, according to Sandler et al., around 13,360 expectant mothers whose Rh (D) type is uncertain receive RhIG when it’s not necessary, meaning an estimated 24,700 doses are administered to patients who don’t need it. The use of RHD genotyping can prevent the excess use of RhIG by identifying those types that can be safely treated as Rh positive and those that need RhIG treatment.

3. Reducing RhD-Related Expenses

In addition to preventing unnecessary use of RhIG, RHD genotyping also minimizes expenses due to the administration of unnecessary blood products. The cost of 24,700 unnecessary RhIG treatments is significant and could be eliminated with the use of RHD genotype testing. In a simulated 10-year span, Kacker et al. (2015) found that RHD genotyping resulted in a net savings of $645,034 across the entire U.S. population. Over 20 years, the expected savings increased to $2.01 million.

The benefits of RHD genotyping are vast, including more accurate and efficient obstetric care and cost savings. It also allows OB-GYNs to develop treatment plans for patients more confidently.

For more on the benefits of RHD genotyping, download and read the Sandler et al. study here.