probability The likelihood that something will happen. For example, a probability of less than .05 indicates that the likelihood of something occurring by chance alone is less than 5 in 100, or 5 percent. This level of probability is usually taken as the level of biologic significance, so a higher incidence may be considered meaningful….
pro time Prothrombin time.
pro- A prefix (from both Greek and Latin) with many meanings, including before, in front of, preceding, on behalf of, in place of, and the same as.
p.r.n. Pro re nata. Abbreviation meaning as needed. See also Appendix A, “Prescription Abbreviations.”
PRK Photorefractive keratectomy.
private mutation A rare gene mutation that is usually found only in a single family or a small population. A private mutation occurs and is passed to a few family members, but not to future generations.
prion A small proteinaceous infectious diseasecausing agent that is believed to be the smallest infectious particle. A prion is neither bacterial nor fungal nor viral and contains no genetic material. Prions have been held responsible for a number of degenerative brain diseases, including mad cow disease, Creutzfeldt-Jakob disease, fatal familial insomnia, kuru, and an unusual…
primum non nocere See first do no harm.
primary teeth The first 20 teeth, which are shed and replaced by permanent teeth. The first primary tooth comes in (erupts) at about 6 months of age, and the last erupts at around 21⁄2 years. Replacement with permanent teeth usually begins at about age 6. Also known as baby teeth, milk teeth, primary dentition, temporary…
primary sclerosing cholangitis A chronic disorder of the liver of uncertain cause in which the bile ducts within and outside of the liver become inflamed, thickened, scarred (sclerotic), and obstructed. This progressive process can in time destroy the bile ducts and lead to cirrhosis. Abbreviated PSC. PSC can occur by itself or in association with…
primary HIV infection See HIV infection, primary.
primary dentition See primary teeth.