Lab Dept:

Hematology

Test Name:

APT, STOOL

General Information

Lab Order Codes:

APT

Synonyms:

Hemoglobin F

CPT Codes:

83033 – Hemoglobin; F (fetal), qualitative

Test Includes:

Qualitative testing for fetal blood in stool or gastric contents. Resulted as positive or negative for fetal blood.

Logistics

Test Indications:

Useful for differentiating between newborn swallowing mother’s blood and fetal gastrointestinal bleeding.

Note: The APT test is used to determine whether blood in the diaper, vomitus, or feces of a neonate contains predominantly the baby’s or the mother’s blood. It is a crude, non-quantitative method based on resistance of hemoglobin F to alkali denaturation.

Lab Testing Sections:

Hematology

Phone Numbers:

Minneapolis:

Saint Paul:

612-813-6280

651-220-6550

Test Availability:

Daily; 24 hours

Turnaround Time:

4 hours

Special Instructions:

This test is useful ONLY on frankly bloody (red) stool or gastric specimens, not tarry (black) specimens.

Specimen

Specimen Type:

Stool or gastric contents

Container:

Leakproof container

Draw Volume:

0.5 – 1 mL stool or gastric contents

Processed Volume:

Minimum: 0.5 mL stool or gastric contents

Collection:

Routine stool or gastric contents collection

Special Processing:

N/A

Patient Preparation:

None

Sample Rejection:

Brown or tarry stools are not acceptable and will be rejected; mislabeled or unlabeled specimens

Interpretive

Reference Range:

Negative for fetal blood

Critical Values:

N/A

Limitations:

Tests performed in cases of melena or with coffee ground material (denatured blood) may produce a false-positive result as oxyhemoglobin has been converted to hematin. Visual judgement of color produced by test procedure may lead to error if only a small amount of blood is present. Bilirubin containing meconium and possibly other substances may cause stool color interference.

Methodology:

Alkaline Denaturation

References:

Apt L, et al, Melena Neonatum, The Swallowed Blood Syndrome, J Pediat, 45:5, 6-12