Cochrane reviews are systematic reviews of published literature that assess the available evidence for and against the effectiveness and appropriateness of healthcare interventions in specific circumstances. A new Cochrane review looks at newborn screening for cystic fibrosis (CF) [Southern KW et al. (2009) Cochrane Database Syst Rev. (1):CD001402], an autosomal recessive genetic disease that causes excess mucus production and salt loss via sweat. This results in potentially severe respiratory and gastrointestinal effects, with a current average life expectancy of 31 (see Cystic Fibrosis Trust website); lung disease and damage cause the most serious pathology, and appear to begin very early in life.
The review addresses the question of whether or not newborn screening CF improves clinical outcomes, quality of life or survival when compared with symptomatic clinical diagnosis, and without serious adverse effects. These might include the effects of false-positive and false-negative results, and of diagnosis of rarer individuals in whom the disease is relatively mild.Two eligible randomised controlled trials of neonatal screening for CF among more than one million newborns were identified, but data from only one study was included in the analysis.
The review authors found that severe malnutrition was less common among screened participants; improved nutrition resulted in better growth, and potentially in improved cognitive function. They found possible benefits in terms of reduced lung disease and damage in the short-term following newborn diagnosis, but not in the longer term. This was attributed to multiple confounding factors that also influenced long-term lung outcomes, such as different CTFR mutations and lung colonization by Pseudomonas aeruginosa bacteria. However, screening costs were found to be lower than for traditional diagnosis. It is worth noting that the trials under review took place 15-25 years ago; since then, the treatment of CF has improved significantly, which would affect how much of an impact earlier diagnosis may have.
Comment: The suggestion that identification of newborns with CF had clinical benefits for the child (as opposed to merely avoiding unnecessary clinical investigations and providing optimal reproductive choice for the parents of an affected child) was originally a contentious one. The first evidence was that early diagnosis improved nutritional outcomes, if not necessarily pulmonary outcomes [Farrell PM et al. (2001) Pediatrics. 107(1):1-13], and this new review supports that finding, which isn’t surprising because it analysed data from the same trial. Perhaps the key point of note from this review is the difficulty of demonstrating or quantifying the effectiveness of particular interventions without the most rigorously designed clinical trials.