I have a pregnant patient with
anti-Kell antibodies (titer is 1:4). What are the recommendations for managing
patients with anti Kell antibodies?
The American College of Obstetricians and Gynecologists
recommends determination of the father’s
red blood cell antigen status as
the first step. To determine the father's Kell antigen status most laboratories
will ask that you submit 5 mL of the father’s blood drawn into a
Lavender-top (EDTA) tube with a request to perform Red Blood Cell
Antigen Typing, Kell antigen, Kell blood group phenotype on the father’s blood.
If the father is negative for the Kell antigen (and it is certain that he is the
father of the fetus) further evaluation is unnecessary. If the father has the Kell antigen or the status of the father is unknown, then amniocentesis to
determine the fetal antigen type should be performed. If the fetus is negative
for the Kell antigen periodic noninvasive assessment is not unreasonable since
there is a low false negative rate associated with this test (1–3%).
Serial antibody titers are commonly used for monitoring fetal status with a
first sensitized pregnancy in Rh disease. However, when an Rh-sensitized mother has had a
previously affected fetus or the mother is Kell-sensitized maternal antibodies do not
appear to correlate well with fetal status. In addition,
amniotic fluid bilirubin measurements may be misleading in
pregnancies complicated by Kell alloimmunization. Ultrasound Doppler measurement of the peak systolic velocity in the fetal middle cerebral
artery (MCA) appears to be a more appropriate means to monitor these pregnancies
for fetal anemia [1-4].
The peak systolic velocity is measured in the MCA closest to the transducer when
the fetus is not active or breathing. The Doppler gate is placed in the center
of the MCA immediately above the Circle of Willis with the ultrasound beam
aligned to the direction of blood flow (angle of insonation of
zero degrees). As a fetus develops anemia the velocity of the blood flow through the
fetal MCA will be expected to increase due to the decreased viscosity of the
fetal blood and increased fetal cardiac output. Patients with a MCA PSV of greater than 1.5
times the median have a high risk for having a severely anemic fetus [5-7] and should be referred for
possible percutaneous umbilical blood sampling to determine whether the fetus
needs to receive a transfusion.
Expected Peak Velocity of Sytolic Blood Flow through MCA
1.McKenna DS, et al. Management of pregnancies complicated by anti-Kell isoimmunization. Obstet Gynecol 1999;93:667–73.
2. Hackney DN, et al., Management of pregnancies complicated by anti-c isoimmunization. Obstet Gynecol 2004;103:24–30.
3. van Dongen H, et al., Non-invasive tests predict fetal anemia in Kell-alloimmunized pregnancies. Ultrasound Obstet Gynecol 2005;25:341
4. American College of Obstetricians and Gynecologists ACOG Practice Bulletin 75: Management of alloimmunization during pregnancy. Obstet Gynecol. 2006 ;108:457-64.
5. Mari G, et al. Diagnosis of fetal anemia with Doppler ultrasound in the pregnancy complicated by maternal blood group immunization. Ultrasound Obstet Gynecol 1995;5:400-405.
6. Mari G, et al. Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses. Fetal blood flow velocity of the middle cerebral artery in the anemic fetus. N Engl J Med 2000;342:9-14.
7. Scheier M, et al. Prediction of fetal anemia in rhesus disease by measurement of fetal middle cerebral artery peak systolic velocity. Ultrasound Obstet Gynecol 2004;23:432-436.