Monitoring the clearance of fetal RhD‐positive red cells in FMH following RhD immunoglobulin administration

Abstract

Anti-RhD immunoglobulin was administered to RhD-negative women based on estimates of fetal bleed size obtained using a direct immunofluorescence flow cytometric technique employing a FITC-conjugated monoclonal human anti-D (BRAD 3). The effectiveness of the dose administered was assessed by (i) measuring the fraction of RhD-positive fetal cells in the maternal circulation at d0, and between d2 and d10 post RhD Ig administration, (ii) quantifying the amount of anti-D detectable in maternal plasma following RhD Ig injection in the perinatal period and (iii) assessing maternal serum for the presence of immune anti-D in follow-up samples taken 3 months to 3 years after delivery. Fifty-four women were assessed, 29 having fetal bleeds in excess of 4 mL. Follow-up samples were received from 20/29 mothers after RhD Ig administration; 43-99% and 69-99% of fetal cells had been cleared by d2/3 and d5/6, respectively, in 14/20 mothers, whereas less than 50% had been cleared in the remaining mothers. Long-term follow-up samples were obtained from eight of the 29 mothers (four with bleeds >/=20 mL, two with bleeds >95 mL): none had detectable anti-D in the serum 4 months to 3 years after delivery despite the persistence of up to 36% fetal RhD-positive cells in the maternal circulation six days after delivery.

Antibody-Mediated Immune Suppression of Erythrocyte Alloimmunization Can Occur Independently from Red Cell Clearance or Epitope Masking in a Murine Model

“…If rapid red cell clearance is not an important or contributing attribute to an AMIS effect, then the selection of such isotypes of Abs could be detrimental. In fact, some indirect evidence suggests that red cell clearance is not strikingly related to a successful AMIS effect in some individuals (4,12,23,50,51), and work from our laboratory using SRBCs as the Ag in a murine model has shown that forcefully directing the sensitized erythrocytes to phagocytic macrophages gave rise to enhancement rather than suppression (52).…”

Detection of massive transplacental haemorrhage by flow cytometry

“…Quantification of Rh(D) positive fetal red cells in the Rh(D) negative maternal circulation at delivery allows precise dosing of Rh(D) immunoglobulin for protection against anti‐D allo‐immunization. Recent reports have shown that flow cytometry is more accurate than the traditional Kleihauer–Betke and other tests for quantification of large FMH (Bayliss et al ., 1991; Johnson et al ., 1995; Lloyd‐Evans et al ., 1996; Bromilow & Duguid 1997; Lubenko et al ., 1999). The accuracy of flow cytometry was evident in this case where reduction in Rh(D) positive cells directly correlated with the dose of anti‐D administered.…”

Does Rh immune globulin suppress HLA sensitization in pregnancy?

“…Similar findings were reported in a 1999 case series of six postpartum women who were treated with RhIG after Kleihauer-Betke testing revealed the presence of large-volume FMH (range: 11.7–153.4 mL). As many as 36% of the D+ fetal RBCs remained detectable in the circulation on day 5–6 post-RhIG administration, yet months later none of the women had become sensitized to D. 22 It is perhaps not surprising that D+ RBCs can sometimes be detected in the circulation several days after RhIG administration. Based on the law of mass action, it has been calculated that in a bleed of 5 mL D+ RBCs treated with 100 mcg RhIG, only 8.7% of D antigen sites would be bound by anti-D. 23 …”