Lab tests are routinely performed to screen newborns for signs of developmental or genetic disorders. Identifying such conditions early – particularly before symptoms develop – can lead to early treatment of the disorder, which is often more effective than treating a problem in a later stage of development. The tests can be particularly useful when rare metabolic disorders are identified. These conditions may involve buildup or inability to process certain chemicals, which may lead to mental retardation or coma and death. Strict diets that avoid certain foods can minimize or eliminate these effects. For this reason, these tests are often lifesaving tools.

The lab tests used to screen newborns do not actually diagnose a condition, but merely indicate that further testing is necessary. In fact, most children who have a positive result after these screenings turn out not to have the disease or disorder (false-positive result).

The best screening tests have low false-negative rates, but may have high false-positive rates. This is because it is more important that a test falsely indicates presence of a disease that is not there than to miss low levels of a disease that is present.

Each state has its own regulations for which screening tests are required of newborns, and the number of tests typically ranges between 3 and 10. Some states require as many as 40 tests. All 50 states screen for congenital hypothyroidism, which involves poor growth and brain development as a result of having low levels of thyroid hormone. When detected early, this condition can be treated with thyroid hormone supplements.

Other conditions that may be screened for – roughly in order of the number of states that require testing for the particular disorder – include:

• Phenylketonuria (PKU). Prevents the body from processing the amino acid phenylalanine, which can build up in the body and cause mental retardation. A special diet low in phenylalanine can help prevent mental retardation.
  
  
• Galactosemia. Prevents the body from converting galactose into another sugar, glucose (blood sugar). In severe cases, eliminating milk and other dairy products from the diet is necessary to prevent blindness, mental retardation, growth deficiency or death.
  
  
• Sickle cell disease. Inherited condition in which the red blood cells become abnormally shaped. It may lead to pain or a number of other serious complications including stroke, life-threatening infection or end-organ damage. Young children with this disorder are at higher risk for bacterial infections such as pneumonia and meningitis. Antibiotics may be prescribed even before symptoms appear in children who test positive for this disease.
  
  
• Biotinidase deficiency. Causes a lack of the enzyme biotinidase, which recycles the B vitamin biotin in the body. This can lead to seizures, lack of muscle control, immune-system problems, hearing loss, mental retardation, coma and death. Biotin supplements can prevent these symptoms.
  
  
• Congenital adrenal hyperplasia. Family of disorders in which adrenal gland hormones are not produced sufficiently. Poor development of the genitals and death may result. Hormone supplements are used to treat this condition.
  
  
• Maple syrup urine disease (MSUD). Causes an inability to process three amino acids. As these amino acids build up in the body, they cause urine to smell like maple syrup. It can lead to mental retardation, physical disability or death. Avoiding certain high-protein foods can prevent these symptoms.
  
  
• Homocystinuria. An enzyme deficiency that can produce dislocated eye lenses, mental retardation, skeletal abnormalities and abnormal blood clotting. A special diet can help prevent these symptoms.
  
  
• Tyrosinemia. Prevents processing of the amino acid tyrosine, which can result in mental retardation, language difficulties, liver problems and death. Treatment typically involves a special diet or liver transplantation.
  
  
• Cystic fibrosis. Inherited condition that causes cells to release thick mucus, which can cause problems with respiration, digestion and growth. There is no cure, although antibiotic therapy may help prevent bacterial infections associated with the disease.
  
  
• Toxoplasmosis. Infection with a parasite that is transmitted through the placenta to a child. It can result in blindness or mental retardation. The value of early detection of toxoplasmosis remains unclear, and only a couple of states require testing for it.

Although each state has its own list of a handful of required lab screenings for newborns, many other lab tests also are available. The March of Dimes suggests more than two dozen tests that parents are urged to consider. However, in many cases medical insurance does not cover the cost of these extra tests.