Joanna asked about why babies' stools became black after being exposed to
home therapy on a bili blanket.  A couple pf days ago, my high-school science
teacher husband asked about why bowel movements are brown. My answer is that
bile contains breakdown products of red blood cells. Iron-containing
components make the stool appear dark. I'll use technical words if that will
make the explanation sound more impressive.

Physiological jaundice occurs because fetal red cells are rapidly broken
down. Sometimes, even more RBC's are phagocytized, such as when there is
extensive bruising or a maternal-fetal blood incompatability exists. Babies'
livers are immature and bilirubin accumulates. When red blood cells are
broken down, most of the heme unit is converted into bilirubin, which is
attached to plasma proteins for transport. Bilirubin is removed from the
blood by the liver and conjugated with glucuronide to render it water-soluble
so that it can be excreted in the bile. (Conjugated bilirubin is the "direct
bilirubin" measurement seen in blood test results.)

Phototherapy (fluorescent light in the blue range of 420-470 nanometer wave
length) converts the bilirubin in the skin to a structural isomer that is
more water soluble and can be excreted in the stool and urine.

Nurses who have cared for babies receiving phototherapy are familiar with the
dark stools. Some pediatricians change diapers; some call the nurse.

Becky Engel, RN, IBCLC
Athens, GA