Resolving variable maternal D typing using serology and genotyping in selected prenatal patients

Area of Science:

• Immunology
• Genetics
• Obstetrics

Background:

• RhIG prophylaxis is crucial for D- pregnant women to prevent hemolytic disease of the newborn.
• Weak D serology interpretation can be variable, leading to inconsistent RHD status determination.
• Genotyping is increasingly recommended for accurate RHD status in cases of weak D serology.

Purpose of the Study:

• To evaluate the utility of a serologic algorithm for selecting patients requiring RHD genotyping.
• To determine the efficiency and cost-effectiveness of genotyping for weak D serology.
• To improve the accuracy of RhIG prophylaxis decisions in pregnant individuals.

Main Methods:

• A serologic algorithm was developed to identify patients needing RHD genotyping.
• Genotyping was performed using commercially available platforms.
• Canadian Blood Services implemented comprehensive prenatal testing and genotyping in four provinces.

Main Results:

• Only 0.4% of D- patients met the criteria for genotyping.
• Most genotyped patients were identified as weak D Type 1, 2, or 3 (61%) or other weak/partial D types (30%).
• RhIG administration was avoided in 66% of cases identified as weak D Type 1, 2, 3, or D+.

Conclusions:

• RHD genotyping, guided by a serologic algorithm, accurately identifies genotypes in most patients with weak D serology.
• This approach effectively identifies individuals not at risk for alloimmunization, allowing for avoidance of unnecessary RhIG.
• Utilizing a serologic algorithm for RHD genotyping selection reduces the number of investigations and associated costs.