Apt–Downey test

Apt–Downey test is a medical diagnostic test used in neonatology to differentiate fetal or neonatal blood from maternal blood. This test is particularly useful in cases of suspected fetal-maternal hemorrhage or when there is the presence of blood in the amniotic fluid or in the neonate's vomit or stool. The Apt–Downey test is based on the principle that fetal hemoglobin is resistant to denaturation by alkali, a property not shared by adult hemoglobin.

Procedure

The Apt–Downey test involves mixing a small sample of the blood in question with a solution of sodium hydroxide (NaOH), which lyses the red blood cells and releases hemoglobin. The solution is then observed for changes in color. Fetal hemoglobin, being resistant to alkali, remains pink, whereas adult hemoglobin is denatured and turns brown or yellow. The test can be performed on fresh or aged stains and does not require sophisticated laboratory equipment, making it accessible for use in various healthcare settings.

Clinical Significance

The Apt–Downey test is significant in the management of neonatal jaundice and in cases where there is a suspicion of hemolytic disease of the newborn. It helps in determining the source of bleeding, which is crucial for appropriate treatment. For instance, if the blood is determined to be of fetal origin, it may indicate the need for further investigation into potential causes of neonatal bleeding, such as vitamin K deficiency bleeding or other coagulopathies.

Limitations

While the Apt–Downey test is valuable, it has limitations. It cannot quantify the amount of fetal-maternal hemorrhage, and a positive test does not necessarily indicate a clinically significant hemorrhage. Additionally, the test's accuracy can be affected by the degradation of blood samples over time or by the presence of certain substances in the blood that may interfere with the color change.

History

The test was developed by Dr. Leonard Apt and Dr. Mary Downey in the 1960s as a simple, rapid method to distinguish between fetal and adult hemoglobin in blood samples. Since its introduction, it has been widely adopted in clinical practice due to its ease of use and the immediate availability of results.

See Also

• Hemolytic disease of the newborn
• Neonatal jaundice
• Fetal-maternal hemorrhage