See also: PAPP-A and screening for Down syndrome
A screening test is an exam that identifies those who are most likely to suffer from it in a population considered at risk for a particular disease.
A classic field of application for screening is oncology. Many types of cancer, in fact, evolve in an extremely slow and asymptomatic or paucisintomatic way, so that an early diagnosis is essential to increase the therapeutic and survival possibilities. Adequate screening can not only save lives, cure disease or alleviate the suffering that comes from it, but even prevent the onset of it, for example by removing intestinal polyps or mammary nodules considered to be at risk of malign evolution.
Let us now look at the main screening tests in the oncology field valid for the general population:
| Cancer | Candidates * | Screening test |
| Breast cancer | Women aged between i 50 and 69 years | Bilateral mammography every two years |
| Tumor of the uterine cervix | Women between 25 and 64 years old | Pap test every three years |
| Tumor of the colorectal colon | Men and women between 50 and i 70/74 years | Search for occult blood in the stool every two years. Between 58 and 60 years rectosigmoidoscopy to be repeated every 10 years. |
The digital rectal exploration and the dosage of PSA (prostate specific antigen), starting from the age of 50, are part of the prostate cancer screening, but their validity - unlike the cases reported in the table - remains controversial.
The word "screening" is a term commonly used in modern medicine that literally means "carefully choose". Screening is a filter to be used in the population to identify people at risk for a given disease.
The purpose of the screening test is therefore to identify the people at greatest risk to whom to offer the possibility of carrying out further investigations.
If the screening test is positive, as anticipated, the patient is subjected to further investigations (because he is not necessarily sick), such as colposcopy (in case of suspected cervical cancer), colonoscopy (in case of suspected tumor of the colon rectum), additional slabs, breast examination and breast ultrasound (in case of suspected breast cancer).
In assessing the opportunity for nationwide screening campaigns, a very long list of factors, such as:
the cost / benefit ratio (justifiable only for pathologies of great epidemiological relevance);
the risk of false positives (subjects in which screening shows a high probability of disease, then denied by subsequent investigations) and their repercussions (psychological stress suffered by patients, affective, working consequences, etc.);
the risk of false negatives (subjects in which screening has a negative outcome despite the actual presence of the pathology) and its repercussions (false sense of security, tendency to abandon any preventive measures or not to undergo subsequent screening).
Another classic area of application of screening is obstetric. In this sense, we first look for any infectious diseases that can harm the fetus, such as toxoplasmosis (toxotest), rubella (rubero-test), syphilis (lue screening), HIV and herpes simplex (which fall within the TORCH), the Cytomegalovirus and a possible maternal-fetal incompatibility (Coombs Test). Very important is also the screening for gestational diabetes (GCT, Glucose Challenge Test ), while any chromosomal alterations are typically evaluated by ultrasound (nuchal translucency), blood tests (tri-tests for Down syndrome) and amniocentesis. Furthermore, immediately after the birth, the unborn child is subjected to the so-called neonatal screening, for the research of some congenital diseases, such as cystic fibrosis, phenylketonuria and congenital hypothyroidism. Once again, this type of screening is justified by the fact that the pathology is not visible at the time of birth and its execution prevents irreversible damage and the death of the child due to diagnostic delays, improving at the same time the course of the pathology and the quality of life individual.
In addition to the traditional examples reported in the article, there are innumerable screening tests for other diseases, which are however carried out only on particular populations at risk, for example due to the familiarity of one or more diseases.
