Apt Test for Swallowed Blood

Test Description

The Apt test for swallowed blood is a test to determine if blood in an infant’s
stool or vomitus is from the mother or from the infant. The test is based on the
fact that a newborn’s blood contains primarily fetal hemoglobin (Hb F). The
mother’s blood, unless she has thalassemia major, is primarily Hb A. When blood
is seen in a newborn’s stool or vomitus, it must be tested to ensure that the newborn
is not having internal bleeding. If bleeding is occurring, immediate treatment
is needed.
To differentiate the type of hemoglobin in the sample of bloody stool or vomitus,
the sample is first mixed with water and then centrifuged, producing a pink
solution. This solution is then tested with sodium hydroxide. If the blood is maternal
blood, the solution will turn brownish yellow, due to the presence of hematin, a
product of the breakdown of Hb A. If the blood is fetal blood, the solution will
remain pink. This is because Hb F is resistant to breakdown by alkali such as
sodium hydroxide.

Normal Values
          Negative for Hb F fetal bleeding (pink solution)
          Positive for Hb A maternal blood (brown/yellow solution)

Possible Meanings of Abnormal Values

Fetal gastrointestinal hemorrhage (pink solution)
Swallowed maternal blood (brown/yellow solution)

Contributing Factors to Abnormal Values

• Sample must have visible blood present. Black tarry stool is not acceptable since the
   hemoglobin has already broken down into hematin.
• False-positive results may occur if the mother has thalassemia major, since in this
  condition, up to 90% of the mother’s blood is Hb F.

Interventions/Implications

Pretest

• Explain to the parent(s) the purpose of the test. Provide any written teaching materials
available on the subject.

Procedure

• Obtain a sample of grossly bloody stool or vomitus.
• Gloves are worn during specimen collection.

   Posttest

• Label the specimen and transport to the laboratory.
• Report abnormal findings to the primary care provider.

Clinical Alert                       
• If the Apt test is positive for fetal hemoglobin, further evaluation of the infant
   will be needed to determine the source of bleeding. Close monitoring of the
   infant is essential.