The haemoglobin alkaline denaturation test was routinely performed in 183 fetal blood samples obtained by cordocentesis for prenatal karyotyping by adding 0.1 ml of the blood into a glass test tube containing 5 ml of water and 0.3 ml of 10 per cent KOH as the alkali reagent. The mixture was agitated gently and read at 2 minutes, at which time it was interpreted as a pure fetal blood sample or contaminated with maternal blood according to the change in colour. In order to determine the accuracy of this test to detect maternal blood contamination, the results were compared with the number of fetal and maternal cells detected by standard cytogenetic techniques in those blood samples obtained from male fetuses (n=97). Among these samples, the haemoglobin alkaline denaturation test gave an adult haemoglobin reaction in two cases (2.1 per cent); both samples showed different degrees of maternal 46,XX cells in the metaphases examined (29 of 30 cells in one case and 2 of 31 cells in the other). Conversely, of the 95 samples which gave a fetal haemoglobin reaction, the cytogenetic analysis did not reveal any maternal cells in the metaphases analysed (median 30 cells, range 20-65). We concluded that the haemoglobin alkaline denaturation test is an accurate method for excluding clinically significant maternal blood contamination of fetal blood samples obtained for prenatal karyotyping. This simple, inexpensive technique provides immediate information and, therefore, can be safely incorporated as a bedside test for analysis during fetal blood sampling procedures.
Copyright 1999 John Wiley & Sons, Ltd.