Methods for quantitating fetal red cells in maternal blood

A Colorado physician who is director of a hospital clinical laboratory and transfusion service has received a notification of an Ortho recall for FETALSCREEN (Jan. 8, 2005).

He wonders which alternative methods people are considering to screen for fetal cells in their maternal population, in the absence of an available Ortho fetal screening test kit. He is of the opinion that a "Du test" and the Kleihauer-Betke (K-B) test have poor sensitivity and specificity, and flow cytometry is expensive. He is also concerned about what they should do about women who were screened with the recalled kits.

Editor's Note: Forum members interested in the flow cytometry method may wish to review two recent discussions on this forum (1, 2).

The following comments have been received.

ADDENDA Jan. 12, 2005

1. Editor's Note: ImmucorGamma just announced that it has a fetal screen kit, product code 0007892 (30-35 tests). They have increased production to cover market needs. Kits are available now for emergencies, with more kits coming available next week.
   
   Immucor advises those who wish to place an order to consider that due to high phone volume, to please use one of the following ordering routes:
   • fax: 770-441-3807
   • e-mail: customerservice@immucor.com
   • "Shop Immucor" (online)
   • call toll free: 1-800-510-5110
     
     
2. Kenneth J. Moise, Jr., M.D., Director of the Division of Maternal-Fetal Medicine at the University of North Carolina at Chapel Hill (attribution used with permission), offers the following comments.
   
   First of all, Dr. Moise suggests that colleagues be familiar with some older literature on RhIG. In the event that RhIG is inadvertently omitted after delivery, some protection has been proven with administration within 13 days; recommendations have been made to administer it as late as 28 days after delivery (first reference). Approximately 1 in 1000 deliveries will be associated with an excessive FMH; risk factors will identify only 50% of these.
   • Bowman JM: Controversies in Rh prophylaxis. Who needs Rh immune globulin and when should it be given? Am J Obstet Gynecol 151:289-94, 1985
   • Ness PM, Baldwin ML, Niebyl JR: Clinical high-risk designation does not predict excess fetal-maternal hemorrhage. Am J Obstet Gynecol 156:154-8, 1987.
   Secondly, in his opinion, obstetricians should be notified of this issue (since they are more likely going to be able to contact their patients). He adds that the OB's may need some education on the issue including what a "workup for Rhesus immune globulin" entails. Some may mistakenly think that the K-B test is routinely undertaken for this screening. Most will not know which test kit their blood bank employs or if flow cytometry is used for initial screening for fetomaternal hemorrhage. In his opinion, the problem is likely to be minimal in that one vial of RhIG will cover most antenatal events except for perhaps motor vehicle accidents and a fetal demise secondary to a fetomaternal hemorrhage. Only one in 1000 postpartum women would be involved. He adds that women delivered in the last 28 days (see reference above) who were screen negative using the recalled kits should be offered a second dose of Rhesus immune globulin after their obstetrician explains the low risk for sensitization. Women who were screened with the recalled kits should undergo antibody testing at 6 months postpartum to identify those who have become sensitized.

ADDENDA Jan. 13, 2005

3. Marian D. Damewood, MD Chair, OB-GYN and Alan E. Caroe, MD Blood Bank Medical Director (attribution used with permission) report that their hospital (York Hospital in Pennsylvania) is in the process of contacting physicians who delivered women who had a negative result when tested with the recalled Ortho FETAL-SCREEN during the past 28 days. Each contacted physician is being told that a fetal-maternal hemorrhage screening test (done at the time of their patient's delivery) might have been falsely negative, causing the laboratory not to perform additional testing that might determine if more than one vial of RHIG was necessary. As a courtesy, each contacted physician may issue a prescription for a Kleihauer blood test (Diagnosis: ICD9 Code 656.13 Rh sensitive) and RX: one vial of RHIG IM. The ordered Kleihauer test, RHIG and its injection will not be charged to the patient. THE KLEIHAUER TEST MAY BE BATCHED AND THE TEST RESULT MAY NOT BE AVAILABLE IMMEDIATELY. The attempt to reach a selected group of women who delivered within the past 28 days is based on the belief that an injection of one additional vial of RHIG may be most effective if given within 3 days of delivery, but may be effective (although with decreasing efficacy) if given up to 28 days after delivery. If the Kleihauer results indicate more than 30 mL of red cells with fetal hemoglobin are in the maternal blood, the existing YORK hospital protocol will cause notification of the ordering physician.

ADDENDA Jan. 18, 2005

4. Editor's comment: Ortho has provided additional information about the Urgent Recall pertaining to the FETALSCREEN. See Ortho Recall Update, including physician notification letter - (a 3-page pdf file).

ADDENDA Jan. 30, 2005

5. Dr. Bruce H. Davis of Trillium Diagnostics, LLC in Maine (attribution used with permission) cautions readers that when using the anti-HbF method for flow cytometric fetal cell counting laboratories should always verify that the concentration of antibody used in flow cytometry will result in no change in fluorescence intensity of fetal RBCs in the range of 0 - 15% fetal cells by testing mixtures of cord blood spiked into adult blood. In his hands, he reports that this is typically seen with 10 microliters of the Caltag anti-HbF product . Other lines of evidence that the HbF method is valid are found in the CAP survey (HBF) where there has never been evidence that the anti-HbF method undercounts fetal cells compared to the Kleihauer method. Additionally, a stabilized control product is available for FMH assays called Fetaltrol that is composed of Rh positive fetal cells in Rh negative adult cells. Every lot of this product is reportedly tested by both anti-D and anti-HbF flow cytometry, in order to demonstrate no difference between the two methods in either the low positive control (0.15% fetal cells) or high positive control (1.5% fetal cells) levels. In summary, in Dr. Davis' opinion the anti-HbF method for FMH, which currently is the only FDA cleared method for fetal cell counting, has been validated in multiple labs over the last five years and found to perform in a reliable fashion superior to the Kleihauer assay, at least when performed properly.

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Ira A. Shulman, MD
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