The patient in question is a six-day-old infant with the complaint of “vomiting blood”. Yesterday, the parents had noticed a small stain on his onesie, which, in retrospect, they now think was blood. Today, after a feed, the infant burped and spit up. In the spit-up, the parents noticed a small amount of bright red, blood. There has been no further bleeding. The infant is feeding well and behaving normally. They brought the spit-up for you to see, on a cloth diaper.
The intern reports that there were no problems with the pregnancy, labor or delivery. The infant was born at term. This is the parents’ first baby. There is no significant family history. The physical exam is completely unremarkable, the baby looks great.
You ask the intern two questions he can’t answer: Was the baby born at home or in the hospital? Is he breast or bottle feeding? He’s willing to go back down the hall and ask but wants to know why these particular points are important. A home birth is important because the baby might not have gotten vitamin K, which is routinely given to newborns in hospitals and birthing centers. This prevents hemorrhagic disease of the newborn, a rare bleeding diatheses that occurs in newborns because of poor clotting associated with vitamin K deficiency leading to a paucity of the vitamin K dependent clotting factors. Breastfeeding is important to ask about because the most common cause of vomited blood at this age is swallowed maternal blood, either from delivery or cracked, raw nipples from breastfeeding.
Ok, the intern is game and the two of you head down the hall to dig a little further. Item 1: baby born in hospital. Item 2: Yes, the baby is breastfeeding and seems to be thriving, but the poor mother’s nipples are raw.
After examining the infant and confirming that yes, he really looks like a rose, you ask to examine mother’s nipples. They are cracked and bleeding. To confirm your suspicion, you send the bloody vomitus to the lab for an Apt test. This is a test which differentiates maternal from fetal blood.
The Apt test comes back positive. You are able to reassure the parents that the baby is fine, recommend some lanolin for the mother’s nipples, and send them on their way. You know what? That really was actually a biscuit.
The Apt test differentiates mother’s blood from baby’s blood by looking at the conversion of oxyhemoglobulin to hematin when you mix it with alkali. Bloody stool or vomitus is mixed with water and spun down. The resulting supernatant is mixed with sodium hydroxide. Adult hemoglobin is readily denatured by this, whereas fetal hemoglobin is more resistant. Therefore, the mother’s hemoglobin will turn brown, whereas the infant’s will remain pink.
If the blood is from the mother and the infant is well, no further evaluation is required.