Increased false positive Down syndrome screening in women with sickle cell anemia.

Objectives: This study seeks to determine whether there is a higher rate of false positive serum screening for Down syndrome in women with sickle cell anemia and, if so, which markers contribute to the false positive screen.

Methods: This is a retrospective cohort study of women who had serum screening between 1998 and 2011. Subjects were women with sickle cell anemia (n = 13), and controls were African American women who did not have that disease (n = 91). The populations were compared using basic inferential statistics.

Results: The positive screen rate was 38.5% (5/13) in women with sickle cell anemia and 7.7% (7/91) in the control population (odds ratio 7.5, 95% confidence interval 1.6-35.8, P = 0.001). At the average age of the cases (25 years), the expected false positive rate is only 2%. The human chorionic gonadotrophin values were significantly higher in cases than controls (2.00 and 1.30 MoM, P = 0.017), whereas levels of other serum analytes were similar. None of the screen positive results were associated with a fetus or neonate affected by Down syndrome.

Conclusions: The false positive Down syndrome serum screen rate is significantly higher in patients with sickle cell anemia than in African American women without that disease. The human chorionic gonadotrophin values were significantly higher in cases than controls, suggesting that placental factors may contribute to the elevated false positive rate. © 2015 John Wiley & Sons, Ltd.