Laboratory methods for Rh immunoprophylaxis: a review.

Area of Science:

• Obstetrics and Gynecology
• Hematology
• Clinical Laboratory Science

Background:

• Rh immune globulin (RhIG) prophylaxis requires accurate estimation of fetomaternal hemorrhage (FMH).
• Estimating FMH volume relies on quantifying fetal red blood cells (RBCs) in maternal circulation.
• Distinguishing fetal from maternal RBCs has historically used blood type or hemoglobin differences.

Purpose of the Study:

• To review laboratory methods for detecting and quantifying fetal RBCs in maternal blood.
• To assess current laboratory practices for FMH detection in US hospitals.
• To evaluate the suitability of different methods for Rh immunoprophylaxis.

Main Methods:

• Literature review of laboratory methods for fetal RBC detection.
• Analysis of College of American Pathologists Fetal RBC Detection Survey data.
• Evaluation of rosette screen, acid-elution (Kleihauer-Betke) assay, and flow cytometry.

Main Results:

• The rosette screen is widely used for D-negative mothers but unsuitable for D-positive mothers or unknown fetal D type.
• The Kleihauer-Betke assay is sensitive but tedious, inaccurate, and difficult to reproduce.
• Flow cytometry provides precise quantification but is not widely available due to logistical and fiscal barriers.

Conclusions:

• Current laboratory methods for FMH assessment present significant limitations for optimal Rh immune globulin dosing.
• The limitations of existing methods highlight a need for more accessible and accurate techniques.
• Flow cytometry shows promise for precise quantification but requires broader implementation for clinical utility.