Comparison of conventional tube technique with automated gel microcolumn assay for antenatal antibody monitoring.

Background and objectives: Timely identification of pregnancies at risk of severe haemolytic disease of the fetus and newborn (HDFN) requires accurate and reproducible antibody titration. This study aimed to establish a critical titre for the gel microcolumn assay (GMA) corresponding to the critical titre of ≥16 for the conventional tube technique (CTT) and to evaluate GMA's suitability for routine antenatal antibody titration.

Materials and methods: Altogether, 147 antenatal plasma samples with clinically significant antibodies were studied, including eight pregnancies requiring intrauterine transfusions (IUTs). Twofold serial dilution titres with CTT were made in parallel with automated GMA. Single-dose red blood cells were used with a concentration of 3.5% for CTT and 0.8% for GMA. The critical titre for GMA was compared with CTT as the gold standard.

Results: GMA titres were on average 2.88 (95% confidence interval [CI]: 2.72-3.05) dilutions higher than CTT titres. At a CTT titre of 16, the sensitivity and specificity of GMA titration were maximum (94%, 95% CI: 81-99 and 92%, 95% CI: 85-96, respectively) at a titre of 128, but one of the eight fetuses (12.5%) requiring IUTs would have been missed. At a GMA titre of ≥64, sensitivity and specificity were 100% (95% CI: 100-100) and 77% (95% CI: 68-84) respectively, but the number of pregnancies requiring clinical monitoring more than doubled (2.5×).

Conclusion: A GMA titre ≥64 could be considered a safe critical value for high-risk assessment. Despite being a fully automated method benefiting the screening laboratory, the additional workload and costs caused by unnecessary monitoring at delivery hospitals were unacceptable.