Apt and Downey developed a simple test for distinguishing maternal from fetal/neonatal blood in the stool of a newborn infant. Adult but not fetal hemoglobin is denaturated after exposure to alkali. This can help distinguish maternal blood swallowed during delivery from acute gastrointestinal bleeding in the neonate.
Reagents
(1) 10% sodium hydroxide (10 grams NaOH dissolved in 100 mL distilled water)
Method:
(1) Bloody stool or meconium from the neonate or a diaper is collected. The specimen should not be tarry or coffee-ground in appearance since any hemoglobin may have been converted to hematin.
(2) Mix a small amount of the collected material with water in a ratio of 1 to 10. Centrifuge and collect the supernatant.
(3) Test the supernatant with a dipstick for blood. If negative there is no need to proceed.
(4) Add 0.2 mL of the sodium hydroxide solution to 10 mL of the supernatant and mix.
(5) Observe the supernatant for a change in color.
Color After Exposure to Sodium Hydroxide
Interpretation
brown, yellow brown, greenish brown (brown indicates hematin)
maternal blood
remains pink
fetal/neonatal blood
Limitations:
• Hereditary persistence of hemoglobin F in the mother could result maternal blood reacting like fetal blood.
• Maternal to fetal hemorrhage or blood transfusion can result in circulating adult red blood cells in the neonate.
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