Evaluation of chemical tests for fetal bleeding from vasa previa

To evaluate different alkaline denaturation tests and compare with hemoglobin electrophoresis and the Kleihauer test, and to identify the simplest and most sensitive test that may help to rapidly show the presence of fetal hemoglobin and establish the diagnosis of fetal bleeding from vasa previa.

Maternal and fetal cord blood were obtained from 20 women with uncomplicated deliveries and the samples were mixed in known concentrations ranging from 0-100% fetal blood. Further samples were prepared in which maternal and fetal blood mixtures were diluted with amniotic fluid so that the final concentration of fetal hemoglobin similarly ranged from 0-100%. Alkaline denaturation tests (Apt, Ogita, Loendersloot), hemoglobin electrophoresis and Kleihauer tests were performed on all 40 samples.

The Apt and Loendersloot tests were clearly positive at 60% concentrations of fetal blood. It took approximately 7 and 4 min, respectively, to complete the tests. The Ogita test was positive from fetal blood concentrations of 20% and took approximately 5 min. Hemoglobin electrophoresis took approximately 1 h to complete and the Hb-F band was present even at 0% concentration of fetal blood and the band became more marked with increasing fetal blood concentration. The Kleihauer test was negative at 0% but positive from 0.01% fetal blood concentration. The test took approximately 45 min to perform.

The Ogita test is the best all round alkaline denaturation test that may help to rapidly identify the presence of fetal hemoglobin and so establish the need to expedite delivery when there is fetal bleeding from vasa previa. It is simple to perform, does not require sophisticated equipment, unlikely to give false positive results, and takes only 5 min. The simplicity of the test makes it attractive for routine use on the labor ward.