Webster's New World Medical Dictionary

prothrombin time
A test that is done to gauge
the integrity of part of the blood clotting process.
Prothrombin time is commonly used to screen for
bleeding disorders as well as to monitor the accu-
racy of blood-thinning treatment (anticoagulation)
with drugs such as warfarin (brand names:
Coumadin, Panwarfin, Sofarin). It measures the
time needed for clot formation after thromboplastin
and calcium are added to plasma. Familiarly known
as pro time.
proto
-
oncogene
A normal gene that, when
altered by mutation, becomes an oncogene that can
contribute to cancer. See 
oncogene.
protozoa
A parasitic single-celled organism that
can divide only within a host organism. For exam-
ple, malaria is caused by the protozoa Plasmodium.
proximal
Toward the beginning, the nearer (or
nearest) distant of two (or more) items. For exam-
ple, the proximal end of the femur is part of the hip
joint, and the shoulder is proximal to the elbow. The
opposite of proximal is distal. See also Appendix B,
“Anatomic Orientation Terms.”
proximal white subungual onychomycosis
See 
onychomycosis, proximal white subungual.
proxy, health care
See 
health care proxy.
pruritic
Itchy. For example, a scab may be
pruritic.
pruritus
See 
itching.
pruritus ani
See 
anal itching.
PSA
Prostate specific antigen. See 
prostate spe-
cific antigen test.
PSC
Primary sclerosing cholangitis.
pseudo
- Prefix indicating a medical condition
that resembles another condition but appears to
have different causes, as in pseudoseizure (a
seizure-like episode that may not show up as
unusual electrical activity in the brain).
pseudodementia
A severe form of depression
that results from a progressive brain disorder in
which cognitive changes mimic those of dementia.
pseudogout
Inflammation of the joints that is
caused by deposits of calcium pyrophosphate crys-
tals, resulting in arthritis, most commonly of
the knees, wrists, shoulders, hips, and ankles.
Pseudogout usually affects only one or a few joints
at a time. True gout is due to a different type of crys-
tal, which is formed by the precipitation of uric
acid.