Rh Incompatibility Workup

Updated: Aug 05, 2022
  • Author: Leon Salem, MD, MS; Chief Editor: Bruce M Lo, MD, MBA, CPE, RDMS, FACEP, FAAEM, FACHE  more...
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Laboratory Studies

Prenatal emergency care

Determination of Rh blood type is required in every pregnant female. [5, 6]

In a pregnant woman with Rh-negative blood type, the Rosette screening test often is the first test performed. The Rosette test can detect alloimmunization caused by very small amounts of fetomaternal hemorrhage. When a high clinical suspicion of large fetomaternal hemorrhage is present (>30 mL blood), the Kleihauer-Betke acid elution test can be performed. The Kleihauer-Betke test is a quantitative measurement of fetal red blood cells in maternal blood, and it can be valuable for determining if additional amounts of Rh IgG should be administered. The amount of Rh IgG required for treatment after sensitization is at least 20 mcg/mL of fetal RBCs.

Point-of-care blood tests have become available for use in the emergency department and have been shown to have very high sensitivity and specificity in determining Rh status. [7]

Obtaining maternal Rh antibody titers can be helpful for future follow-up care of pregnant females who are known to be Rh negative and may be initiated from the ED. High levels of maternal Rh antibodies suggest that Rh sensitization has occurred, and further studies, such as amniocentesis and/or cordocentesis, may be necessary to evaluate the health of the fetus.

Postnatal emergency care

Immediately after the birth of any infant with an Rh-negative mother in the ED or prehospital setting, examine blood from the umbilical cord of the infant for ABO blood group and Rh type, measure hematocrit and hemoglobin levels, perform a serum bilirubin analysis, obtain a blood smear, and perform a direct Coombs test.

A positive direct Coombs test result confirms the diagnosis of antibody-induced hemolytic anemia, which suggests the presence of ABO or Rh incompatibility.

Elevated serum bilirubin measurements, low hematocrit, and elevated reticulocyte count from the neonate can help determine if an early exchange transfusion is necessary.

An emergent exchange transfusion, preferably performed in a neonatal intensive care setting with experience in this procedure, is required in infants born with erythroblastosis fetalis, hydrops fetalis, or kernicterus.

Other testing

Perform fetal monitoring in cases of suspected fetal distress. Abnormal fetal heart tones and ultrasonographic evidence of fetal or placental injury are indications of worsening fetal condition requiring emergent delivery, ideally in a center specializing in high-risk obstetric care.


Imaging Studies

In the ED, ultrasonography of a pregnant female with suspected Rh incompatibility is limited to pelvic ultrasonography. Fetal ascites and soft tissue edema are definite signs of severe involvement.

Once hydrops fetalis has developed, the sonographic evidence includes scalp edema, cardiomegaly, hepatomegaly, pleural effusion, and ascites.