24. NEONATAL SCREENING
Many countries have instituted programmes for screening all newborn infants for certain inherited metabolic disorders or congenital defects. The criteria should depend on the following characteristics of the disorder or of the test:

25. The disease should not be clinically apparent at the time of screening and should have a relatively high incidence in the population screened.
The disease should be treatable or early treatment should improve outcome.
It must be possible to obtain the result of the screening test before irreversible damage is likely to have occurred.
The screening test should be simple and reliable and the cost of the programme should, ideally, be at least partly offset by the cost savings resulting from early treatment. For example, such treatment may sometimes eliminate the need for prolonged institutional care.

26. Not all these criteria are necessarily fulfilled in all screening programmes .
In the UK, at between 5 and 8 days, babies are screened for certain conditions by taking a small capillary blood sample from a heel prick.
Blood spots are placed on a paper card, which can be posted to the regional laboratory for assay.In the UK, screening is generally carried out for neonatal hypothyroidism and PKU. Other conditions that may be screened for in certain regions include cystic fibrosis, sickle cell disease or thalassemia

27. PRENATAL SCREENING
Prenatal screening, of high-risk groups only, may be performed for some disorders in order to plan the appropriate place and method of delivery for the well-being of the infant or to offer termination, if the diagnosis is made early enough and if it is acceptable.

28. Prenatal screening for inherited metabolic disorders most commonly involves demonstrating the metabolic defect in cultured fetal fi broblasts obtained by amniocentesis early in the second trimester, or by chorionic villus sampling during the fi rst trimester. Examples of those groups in whom such screening may be indicated include women with a previously affected infant and ethnic groups thought to have a relatively high incidence of the carrier state, such as of Tay–Sachs disease in Ashkenazi Jews. In these high-risk populations, screening is often performed before conception, enabling genetic advice and prenatal diagnosis to be offered to couples who are carriers