Workup Following a Positive Indirect Coombs Test

Initial Evaluation

The American College of Obstetricians and Gynecologists recommends a detailed ultrasound with fetal echocardiography, maternal history assessment, and middle cerebral artery (MCA) Doppler evaluation to assess for fetal anemia in cases of positive indirect Coombs test 1, 2
A positive indirect Coombs test indicates the presence of circulating antibodies in maternal serum that can potentially cause immune-mediated hemolysis 3
Perform detailed ultrasound including fetal echocardiogram to evaluate for structural abnormalities and hydrops fetalis 2
Obtain maternal history including family history, medications, and potential exposures 2
Perform MCA Doppler evaluation to assess for fetal anemia (peak systolic velocity >1.5 MoM indicates anemia) 1, 2

If structurally normal fetus, perform amniocentesis for PCR for infectious agents (parvovirus, CMV, toxoplasmosis) if clinically indicated 2
Evaluate parents: Mean corpuscular volume (MCV) of parents (if <80 fL, consider alpha-thalassemia testing) 2
Consider lysosomal enzyme testing if available and no other etiology identified 2

If fetal anemia is detected (MCA PSV >1.5 MoM), test for G6PD deficiency, pyruvate kinase deficiency if no other etiology found 2
Evaluate for fetomaternal hemorrhage (Kleihauer-Betke test or flow cytometry) 2
If hydrops fetalis is present, evaluate for treatable causes that may require urgent intervention 1
Consider referral to a specialized maternal-fetal medicine center 1
Monitor for development of maternal mirror syndrome (serial evaluation of maternal blood pressure) 1

Pregnancies with potentially treatable etiologies should be considered for corticosteroid therapy and antepartum surveillance 1
Delivery should occur at a center capable of stabilizing and treating critically ill neonates 1
Preterm delivery should only be undertaken for specific obstetric indications, as prematurity worsens prognosis 1
Development of maternal mirror syndrome is generally an indication for delivery 1

Do not delay workup for fetal anemia, as timely intervention with intrauterine transfusion can be lifesaving 2