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Introduction ⬇

The Apt test, also known as the alkali denaturation test, was developed by Dr. Leonard Apt for 
identifying the swallowed blood syndrome. The swallowed blood syndrome refers to bloody stools usually passed on to a newborn in the second or third day of life. The blood may be swallowed during delivery or may be from a fissure of the mother’s nipple in breast-fed infants. This condition must be differentiated from GI hemorrhage of the newborn. The test is based on the fact that the infant’s blood contains largely fetal hemoglobin (HbF), which is alkali resistant. This blood can be differentiated from the mother’s blood using laboratory methods.

The Apt test is used to differentiate swallowed blood syndrome from infant GI hemorrhage or blood from the mother. The test can be done on stool or vomitus. Test result will indicate whether blood present in newborn stool or vomitus is of maternal or fetal origin.

Qualitative findings: The specimen is dissolved and treated with 1% NaOH (5:1 ratio) for alkali denaturation. If the blood is of fetal origin, the solution remains pink. If the blood is of maternal origin, the mixture will turn a yellowish brown. HbF is more resistant to alkali denaturation than adult hemoglobin.

Normal Findings ⬆ ⬇

Negative

Procedure ⬆ ⬇

  1. Collect a random, fresh specimen from a newborn infant. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.

  2. The following are acceptable specimens:

    1. Blood-stained diaper

    2. Grossly bloody stool

    3. Bloody vomitus or gastric aspiration

  3. Place specimen or specimens in a biohazard bag and deliver to the laboratory as soon as possible. Refrigerate the specimen or specimens if there is any delay.

Clinical Implications ⬆ ⬇

  1. HbF, which is pink in color, is present in gastric hemorrhage of the newborn.

  2. Adult hemoglobin, which is brownish in color, is present in swallowed blood syndrome in the infant.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain purpose of test, procedure for stool collection, and interfering factors to the parent(s) or guardian(s).

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the parent(s) or guardian(s) regarding abnormal findings; explain the need for further testing and possible treatment for infant GI hemorrhage.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. The test is invalid with black, tarry stools because the blood has already been converted to hematin (stimulates the synthesis of globin).

  2. The test is invalid if there is insufficient blood present; grossly visible blood must be present in the specimen.

  3. Vomitus with pH less than 3.9 produces an invalid test result.

  4. The presence of maternal thalassemia major produces a false-positive test result because of increased maternal hemoglobin F.