February 2021 — Transfusion Medicine Case 1
The lab receives a blood sample from Maternal Fetal Medicine with an order to perform a Fetomaternal Bleed, Flow Cytometry test. The mother is Rh negative, and the team needs to know how much Rh Ig to administer. When the sample is run, it is determined that the mother has a hemoglobinopathy — hereditary persistence of fetal hemoglobin — that complicates the interpretation of the results.
How can the lab assess whether a fetal maternal hemorrhage has occurred?
- Obtain a new blood sample and perform a Kleihauer-Betke test to assess the presence of fetal cells.
- There is no means by which fetal red blood cells can be distinguished from maternal red blood cells positive for hemoglobin F. Advise the team to monitor for other signs of fetal distress.
- Obtain a new blood sample and order a flow cytometry test that includes an antibody for CD36.
- Obtain a new blood sample and order a flow cytometry test that includes an antibody for carbonic anhydrase.
The correct answer is ...
The diagnosis in this case is: Obtain a new blood sample and order a flow cytometry test that includes an antibody for carbonic anhydrase.
Correct answer: By ordering a flow cytometry test that includes antibodies for hemoglobin F (HbF) and carbonic anhydrase (CA), one could discriminate between fetal and maternal HbF+ cells. Fetal RBCs will be negative for CA while the mother’s RBCs will stain positive for both HbF and CA. Incorrect answers: There are multiple methods to identify HbF+ cells.1 Unfortunately, the Kleihauer-Betke assay is a quantification test and is not able to reliably separate maternal and fetal HbF+ cells.2 The same is true when running a flow test with a CD36 antibody, which will label both maternal and fetal cells as well as other cell types, preventing proper interpretation of the flow results.3
- Kim, Y.A. and Makar, R.S. (2012), Detection of fetomaternal hemorrhage. Am. J. Hematol., 87: 417-423. doi:10.1002/ajh.22255
- Krywko DM, Yarrarapu SNS, Shunkwiler SM. Kleihauer Betke Test. [Updated 2020 Sep 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK430876/
- van Schravendijk, M. R., Handunnetti, S. M., Barnwell, J. W., & Howard, R. J. (1992). Normal human erythrocytes express CD36, an adhesion molecule of monocytes, platelets, and endothelial cells. Blood, 80(8), 2105–2114.
Ashley Krull, Ph.D.
Fellow, Cellular Therapy
Margaret DiGuardo, M.D.
Senior Associate Consultant, Laboratory of Transfusion Medicine and Clinical Genomics