Although the use of gel microcolumn assay (GMA) can help identify individuals at risk of severe hemolytic disease of the fetus and newborn (HDFN), the tool may also incorrectly classify healthy pregnancies as high-risk, according to findings recently published in Vox Sanguinis.
Currently, the conventional tube technique (CTT) is the gold standard for HDFN screening. However, this method is very time-consuming and susceptible to substantial variability.
In recent years, many laboratories have transitioned to GMA, an automated tool that is easier to use and less prone to variability than CTT. In this study, the authors sought to establish an antibody threshold for identifying pregnancies at high risk of HDFN using GMA.
The study included 147 blood plasma samples from 91 pregnant women with antibodies linked to HDFN. Among these participants, eight received intrauterine transfusion (IUT). Both CTT and automated GMA were applied to all samples to compare their utility.
Read more about HDFN testing and diagnosis
Findings revealed that a GMA titer of 64 corresponded to 100% sensitivity, meaning that all patients at high risk of developing severe HDFN were classified as such using this threshold. However, the specificity was only 77%, meaning that 23% of low-risk pregnancies were incorrectly classified as high-risk using this threshold. Furthermore, when analyzing anti-D antibodies in particular, the specificity of the test dropped to 52%.
Based on this false positivity rate, switching from CTT to GMA would result in increased clinical monitoring for over twice as many pregnancies, many of which would not require such intervention.
Additionally, even when raising the GMA threshold to from 164 to 128, one of the eight high-risk pregnancies requiring IUT was missed.
The authors suggest that laboratories use GMA as a first pass to identify potential high-risk cases of HDFN, then apply CTT to confirm which patients require follow-up.
“Despite being a fully automated method benefiting the screening laboratory, the additional workload and costs caused by unnecessary monitoring at delivery hospitals were unacceptable,” the study concluded.
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