Webster's New World Medical Dictionary

beta carotene
A protective antioxidant vitamin
that is a natural component of carrots. See also
Appendix C, “Vitamins.”
beta cell, pancreatic
A cell that makes insulin
and is found in the areas of the pancreas called the
islets of Langerhans. Destruction of beta cells
causes type 1 (insulin-dependent) diabetes melli-
tus. See also 
diabetes mellitus.
beta error
The statistical error (said to be “of the
second kind,” or type II) that is made in testing
when it is concluded that something is negative when
it really is positive. Also known as false negative.
beta-2 microglobulin
A nonspecific test that
measures the amount of cell destruction present. It
is considered to be one of the best ways to measure
the progression of HIV-related disease, although it
may also indicate cell destruction due to
cytomegalovirus or other causes.
beta-adrenergic blocking drug
See 
beta
blocker.
bezoar
A clump or wad of swallowed food or
hair. Bezoars can block the digestive system, espe-
cially the exit of the stomach. A bezoar composed of
hair is called a trichobezoar. A bezoar composed of
vegetable materials is called a phytobezoar. A
bezoar composed of hair and food is called a tri-
chophytobezoar.
BF
Physician’s shorthand for black female.
bi-
Prefix indicating two, as in biceps (a muscle
with two heads) or bicuspid (having two flaps or
cusps).
bias
In a clinical research trial, the effects that
may cause an incorrect conclusion. Common exam-
ples of bias include advanced knowledge of the
treatment being given, strong desire of the
researcher for a specific outcome, or improper
study design. To avoid bias, a blinded study may be
done. See also 
blinded study; double-blinded
study.
bicarbonate
In medicine, bicarbonate usually
refers to bicarbonate of soda (sodium bicarbonate,
baking soda), a white powder that is a common
ingredient in antacids. Also, the bicarbonate level is
an indirect measure of the acidity of the blood that
is determined when electrolytes are tested. The nor-
mal serum range for bicarbonate is 22–30
mmol/liter.
biceps
A muscle that has two heads, or origins.
There is more than one biceps muscle. The biceps
brachii is the well-known flexor muscle in the upper
arm; it bulges when the arm is bent in a C-shape
with the fist toward the forehead. The biceps
femoris is in the back of the thigh.