Mini-symposium: newborn screening for inborn errors of metabolism--clinical effectiveness.

With the application of tandem mass spectrometry, newborn screening has become an important topic in inborn metabolic disease. The aim of newborn screening is to produce an improved clinical outcome by early detection of disease, but it has been difficult to measure clinical effectiveness. Good evidence of clinical effectiveness has been hard to obtain because of the rarity of individual disorders, often precluding randomized controlled trials, the increase in diagnosis of individual disorders by screening, compared with clinical diagnosis, variable definitions of what constitutes a case, uncertainty about completeness of ascertainment, and differences in treatment in different geographical areas or at different times. Multiplex testing has introduced some new problems. There have been recent attempts to standardize screening in several countries, which have taken different approaches. Public pressure has driven the introduction of screening for inborn errors in some areas. Since it seems inevitable that screening may often be implemented ahead of hard evidence of benefit, ongoing evaluation of clinical effectiveness is a necessary part of any screening programme.