Webster's New World Medical Dictionary

absolute CD4 count
The number of “helper” T-
lymphocytes in a cubic millimeter of blood. The
absolute CD4 count is frequently used to monitor
the extent of immune suppression in persons with
HIV because with HIV, this number declines as the
infection progresses. Also known as T4 count.
absorption
Uptake. For example, intestinal
absorption is the uptake of food (or other sub-
stances) from the digestive tract.
abstinence
The voluntary self-denial of food,
drink, or sex. Today, abstinence most commonly
refers to denial of one’s sexual activity.
abuse, child
See 
child abuse.
abuse, elder
See 
elder abuse.
a.c.
Abbreviation of the Latin phrase 
ante cibum,
meaning “before meals.” See also Appendix A,
“Prescription Abbreviations.”
AC joint
See 
acromioclavicular joint.
acanthosis nigricans
A skin condition charac-
terized by dark, thickened, velvety patches, espe-
cially in the folds of skin in the armpit, groin, and
back of the neck. It can occur with endocrine dis-
eases such as Cushing disease and diabetes mellitus,
from tumors of the pituitary gland, underlying malig-
nancies, certain drugs, and as a genetic disorder. It
is most common in people who have insulin resist-
ance—those whose body is not responding cor-
rectly to the insulin that they make in their pancreas.
acapnia
Lower than normal level of carbon dioxide
in the blood. The opposite of acapnia is hypercapnia.
accelerated phase of leukemia
Chronic myel-
ogenous leukemia that is progressing. In this phase,
the number of immature, abnormal white blood
cells in the bone marrow and blood is higher than
in the chronic phase, but not as high as in the blast
phase.
accessory nerve
The eleventh cranial nerve,
which emerges from the skull and receives an addi-
tional (accessory) root from the upper part of the
spinal cord. It supplies the sternocleidomastoid and
trapezius muscles.