Application of the hemoglobin alkaline denaturation test to determine the fetal origin of blood: applicability to funipuncture.

Abstract

In funipuncture, fetal blood is collected by passing a needle transabdominally into an umbilical vessel under ultrasound guidance. The objective of this study was to develop an accurate, inexpensive test that immediately indicates the source of the blood during the umbilical sampling procedure, ie, before the needle is withdrawn. To distinguish fetal from adult blood, we used a modified version of the Apt test, which is based on the different alkaline denaturation properties of adult hemoglobin and fetal hemoglobin. We collected 18 blood samples from adult volunteers and 22 umbilical cord samples from deliveries occurring between 25-42 weeks' gestation. The samples were tested for character and time of color change upon addition of increasing concentrations of NaOH. We found 0.2N NaOH to be the ideal concentration to add to hemolyzed blood samples for a reliable determination of blood origin. All of the hemolysates tested in blinded trials using 0.2N NaOH were correctly identified as fetal or adult. The increase in adult hemoglobin due to the increase in gestational age alters the rate of color change, but the difference was not clinically important because it did not alter the efficacy of the alkaline denaturation test.