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Suntaree Apibal, Department of Pathology, Faculty of Medicine, Ramathibodi Hospital, Bangkok 10400 (Thailand) The presence of fetal red cells (F cells) in the maternal circulation is an indicator of a fetomaternal hemorrhage which may subsequently lead to hemo-lytic disease of the newborn [1]. However, a small amount of F cells were found in some normal adults [4] whereas the increase in hemoglobin F production might be increased in various conditions as thalassemia trait, unstable B chain variant and pregnancy [4]. In Thailand, thalassemia hemoglobin E-trait, ß-trait and α-trait were commonly found [2, 3]. The incidence of E-trait is 13% on average in the central region, 40% in the northeast, 8% in the north and 12% in the south [2]. The incidence of ß-trait is 3–9% and of α-trait is 20–30% [3]. So, the study for the percentage of F cells among these groups of subjects may be able to differentiate the false positive results of fetomaternal hemorrhage from F cells found in some normal persons and subjects with the thalassemia trait. F cells could be demonstrated in the maternal circulation by acid elution techniques. Our study revealed the presence of F cells in each group by the Saquan-sermsri acid elution technique as follows. The air-dried blood smear of not over 24 h was fixed in 80% ethanol for 3 min, then immersed in acid/alcohol/ami-do black solution for 3 min at room temperature (100 mg amido black B CI No. 20470, Merck’s Reagenzien, FRG, in 100 ml of 80% ethanol, pH adjusted to 2 with HC1). The smear was washed with tap water for 15 s and air dried. The stained smear was examined under an oil immersion microscope. The percentage of F cells (X ± SD) in 30 normal persons, 30 with E-trait, 30 with ß-trait and 30 with α-trait were 0.14 ± 0.18, 0.92 ± 0.78, 2.3 ± 1.87, and 0.5 ± 0.45, respectively. So, more investigations to exclude these conditions were needed before diagnosing fetomaternal hemorrhage. Thus, the diagnosis of fetomaternal hemorrhage is only valid in the presence of F cells in the maternal circulation if there are no such hemoglobinopathies in the mother. References Fanaroff AA, Martin RJ, Merleatz IR: Behrman’s Neonatal Perinatal Medicine, Disease of the Fetus and Infant, ed 3. St. Louis, Mosby, 1983. Na-Nakorn S, Minnich V, Chernoff A: Studies on hemoglobin E. II. The incidence of hemoglobin E in Thailand. J Lab Clin Med 1965;47:490. Wasi P, Na-Nakorn S, Pootrakul S, Sookanek M, Disthasong-chan P, Pornpatkul M, Panich V: Alpha and beta thalassemia in Thailand. Ann NY Acad Sci 1969;165:60.