(794) The Screening Accuracy of Betke-Kleihauer Test for Fetal-Maternal Hemorrhage in the Antepartum and Postpartum Period

Accurate detection of fetomaternal hemorrhage (FMH) is important both antenatally (e.g., cases of abdominal trauma) and postpartum (to guide the RhIg dosage in RhD-negative patients). Betke-Kleihauer (BK) is the most commonly used quantitative screening test for FMH, but data on its screening accuracy in specific circumstances and the optimal screening threshold are conflicting. The current study aimed to estimate the screening accuracy of the BK test for large FMH and identify the optimal screening threshold in the antepartum and postpartum periods.

Study Design:

A retrospective cohort study of patients who had a BK test at a single center (2014-2022). The definitive diagnosis of large FMH (≥ 15 mL) was done by flow cytometry that was sent in cases of a positive BK test (≥ 2 mL). The screening accuracy of the BK test for large FMH was described using the area under the ROC curve (AUC), detection rate (DR), and false-positive rate (FPR), and was stratified by the timing of testing (antepartum vs. postpartum).

Results:

A total of 4,628 patients underwent BK testing during the study period, 2217 (47.9%) antenatally and 2,411 (52.1%) postpartum. The incidence of a positive BK was 9.1%. The discriminative accuracy of the BK for large FMH was high in the entire cohort (AUC 0.97 [95%-CI 0.94-0.99]) but was lower during the antepartum vs. postpartum period (0.88 [0.80-0.96] vs. 0.997 [0.94-1.00], p=0.02). The highest BK threshold providing a DR of 100% for large FMH was 2.0 mL (FPR of 67% [58%-76%]). A higher BK threshold of 7.5 mL was associated with a reduced DR (81% [85%-97%) and lower FPR (9% [3%-15%]). This threshold (7.5 mL) maintained a DR of 100% in the postpartum period (DR 100%, FPR 8% [3%-14%]) but performed poorly antepartum (DR 57% [47%-67%], FPR 14% [7%-20%]).

Conclusion:

The BK test is associated with a high FPR when using a conservative threshold of 2 mL that provides a 100% DR. Its screening accuracy is higher during the postpartum period, where a less strict threshold of 7.5 mL maintains the same DR of 100% with a lower FPR.