APT Test

Synonyms

Apt Test for Swallowed Blood Syndrome, Fetal Hemoglobin Test in Newborn

Abstract

This test uses the alkali denaturation of fetal hemoglobin to determine whether blood found in a newborn’s stool comes from swallowing the mother’s blood or from perinatal/neonatal GI hemorrhage.

Specimen

Bloody vomitus or mucus, a bloody diaper, or visibly bloody (red) stool.

Container

Send a blood-stained diaper instead of a clean, non-contaminated glass or plastic container for the specimen.

Reason to Reject Sample

Reject if there is evidence of melena or coffee-ground aspirate, or if the specimen is not visibly bloody.

Reference Range

Report indicates whether hemoglobin is of maternal (adult) or fetal origin.

Use

To differentiate swallowed maternal blood from neonatal gastrointestinal bleeding. Rarely performed.

Limitations

The sample must be red and bloody. A false-positive may occur with melena or denatured blood due to oxyhemoglobin converting to hematin.

Methodology

Alkali denaturation test using 1% NaOH:

Mix one volume of bloody stool or vomitus with five volumes of water to make a hemolysate.
Centrifuge the mixture at 2000 rpm for 1–2 minutes.
Fetal hemoglobin (alkali-resistant) stays pink.
Maternal hemoglobin becomes yellow-brown alkaline hematin.

If supernatant remains pink, fetal blood is present. Newborn’s own blood should be tested as a control to confirm.

Additional Information

Swallowed blood syndrome typically appears on day 2 or 3 of life, with bloody stools or vomit. This may result from blood swallowed during delivery or from a nipple fissure during breastfeeding.

The test distinguishes this benign condition from serious neonatal gastrointestinal hemorrhage. Fetal hemoglobin comprises >60% of newborn blood and resists alkali degradation, unlike maternal hemoglobin. APT Test aids in clinical diagnosis when other symptoms and history are inconclusive.

References

Apt L. “Melena Neonatorum.” J Pediatr. 1955;47:1–5.
Berry R, Perrault J. “Gastrointestinal Bleeding.” Pediatric Gastrointestinal Disease. 1991:111–31.
Mougenot JF. “Gastrointestinal Haemorrhage.” Paediatric Gastroenterology. 1992:446–57.
Jacobs et al. “Laboratory Test Handbook.” Lexi-Comp Inc, 1994.