Application of the Doppler Ultrasound in detecting foetal anaemia caused by anti-Kell maternal alloimmunisation: systematic review and meta-analysis

Background: Past studies have examined the Doppler ultrasounds ability to detect foetal anaemia however few focus on Anti-Kell, rather centring on maternal alloimmunisation as a whole. Anti-Kell has proven to be clinically significant in haemolytic disease of the foetus and newborn (HDFN) due to the suppression of erythroid progenitor cells and the absence of typical signs of anaemia. For these reasons, regular procedures to detect foetal anaemia are unreliable with Anti-Kell. Therefore, a systematic review and meta-analysis was performed to investigate the reliability of the Doppler ultrasound in Kell-sensitised pregnancies. Methods: PubMed, SCOPUS, Google Scholar and ProQuest were searched from January 2012 to August 2022 for eligible Doppler ultrasound studies with Anti-Kell specific data. A manual search was performed using relevant references. Results: Five studies were included in the meta-analysis for two-arm proportion. The Doppler ultrasound correctly identified foetal anaemia in 87.4% of Kell cases (Arcsine risk difference [ARD], 0.874; 95% Confidence Interval [CI], 0.667-1.080; I2=0%; p-value=<0.001). Four studies were included in the meta-analysis for sensitivity and specificity. The Doppler ultrasound detecting Kell-specific foetal anaemia had a sensitivity of 83% (CI, 62.9%-93.4%; I2=0%; p-value=0.003) and a specificity of 82% (CI, 52.7%-94.9%; I2=0%; p-value=0.035). Conclusion: In regards to foetal anaemia with Anti-Kell the Doppler ultrasound correctly detected 87.4% of cases with a sensitivity of 83% and specificity of 82%.