- See test.- contrast sensitivity t. examination of the visual recognition of the variation in brightness of an object.- genetic t. laboratory studies of human blood or other tissue for the purpose of identifying genetic disorders. Relatively large chromosomal abnormalities such as deletion or transposition are identified by microscopic examination of chromosomes from a cell undergoing mitosis (karyotyping). More subtle aberrations can be detected by DNA probes (fabricated lengths of single-stranded DNA that match parts of the known gene). Genetic t. in the broadest sense includes biochemical t. for abnormal substances, or abnormally high or low concentrations of normal substances, that serve as markers of genetic deficiency or abnormality. SYN: DNA diagnostics.Genetic t. has become a standard procedure in a number of settings: screening for genetic diseases such as hemochromatosis, screening of couples planning to have children for the cystic fibrosis carrier state, and screening for genetic mutations known to increase the risk of certain cancers such as retinoblastoma and early-onset breast cancer. In addition, genetic profiling (“genetic fingerprinting”) can establish or rule out identity of source for 2 specimens of human material, or parent-child relationship between 2 persons, with a probability of 99.9%. The availability of tests to diagnose or predict untreatable disorders such as Huntington chorea and to identify persons at increased risk of malignant disease has raised many social, psychological, therapeutic, and legal questions. Authorities recommend that people about to undergo genetic t. receive advance counseling about the implications of positive or negative test results. Lay persons often misunderstand the concept of predisposition or risk, particularly with respect to oncogenes. The majority of people who develop cancer do so because of spontaneous genetic mutation, not because of inherited risk; and of those who inherit the risk, not all develop cancer. The discovery that certain populations, such as Ashkenazic Jews, Mormons, and Amish, have a much higher incidence of certain genetic disorders has threatened to reactivate or reinforce ethnic, racial, and religious prejudices. Social groups most likely to harbor easily identified genetic mutations are by definition those whose gene pools are most distinct, because they have tended to intermarry rather than to mix with outside populations. The 1.3% of Ashkenazic Jews who share a mutation on the BRCA2 tumor suppressor gene may all be descendants of a single person (founder effect). The possibility of identifying a person's genetic predisposition to severe, chronic, or disabling diseases raises the possibility of discrimination by employers and by health, life, and disability insurers. State governments and the federal government have established rules that limit the access of employers and insurers, actual and potential, to a person's genetic profile, and that forbid stigmatization, job discrimination, and refusal to issue insurance or to insure at standard rates, because of genetic profile.- proficiency t. a program in which specimens of quality control material are periodically sent to members of a group of laboratories for analysis, with each laboratory's results compared with those of its peers. SEE ALSO: proficiency samples, under sample.- reality t. in psychiatry and psychology, the ego function by which the objective or real world and one's subjectively sensed relationship to it are evaluated and appreciated; the ability to distinguish internal from external events.- susceptibility t. the determination of the ability of an antibiotic to kill or inhibit the growth of bacteria.
* * *test·ing (testґing) administration of a test or tests.
Medical dictionary. 2011.