Neonatal screening today is recognized nationally as an essential preventive public health program. While screening strategies may differ from country to country, they have the common aim of early identification of disorders that can lead to potentially catastrophic health problems.
The newborn screening laboratory must meet the challenge of assisting in detecting disorders by providing efficient and effective laboratory services.
The introduction of filter paper as a collection and transport medium for blood specimens started a highly significant new era in mass screening and preventive medicine.
The results of screening tests reflect qualitative assessment of each infant's clinical status as (affected), (not affected) or (indeterminate) for any given disorder. Confirmatory tests are then used, as part of the follow up process, to establish definitive diagnosis and confirm screening test results.
The following paragraphs represent some disorders in which neonatal screening is essential:
Congenital Hypothyroidism (CH):
CH is a condition found in newborns signaling improper function of the thyroid. Normally TSH levels surge after birth, triggering a rise in thyroid hormone, which is essential for neurological development. In primary CH, the thyroid gland doesn't respond to TSH stimulation, resulting in diminished thyroid hormone levels and elevated TSH levels. It occurs in girls 3 times more often than boys. Early detection and treatment is critical as CH can result in growth failure, deafness, neurological abnormalities, mental retardation and cretinism.
PKU is the most common inborn error of amino acid metabolism; it can lead to mental retardation when untreated. Early detection coupled with restricted phenylalanine intake might prevent mental retardation. Common clinical symptoms of PKU may include convulsions, hyperactivity, reduced head circumference and eczema. Unfortunately, diagnosis from symptoms seldom occurs before six months and usually after signs of mental retardation.
Galactosemia is an inherited disorder of galactose metabolism, caused by a deficiency in one of three enzymes. Elevated circulating galactose concentrations, if untreated, cause vomiting, diarrhea, hepatomegaly, cataracts and mental retardation which can be ameliorated by the prompt removal of milk from diet. However, delayed treatment leads to these chronic symptoms becoming irreversible with an increased risk of death from bacterial sepsis.
Glucose -6- phosphate dehydrogenase, an enzyme found in most body cells, is part of glucose metabolism. G6PD deficiency is a hereditary, sex - linked condition with clinical disease found mostly in males. G6PD deficiency impairs the salability of red cell membranes and makes red cells susceptible to destruction by strong oxidizing agents. Affected patients are at risk for hemolytic anemia, which can be induced by exposure to certain drugs and foods. Some people of Mediterranean origin inherit severe forms of the disease. The ingestion of fava beans may also elicit hemolytic episodes in some affected Caucasians. Early detection is important to avoid inducing factors.
Congenital Adrenal Hyperplasia (CAH):
CAH results from a recessively inherited defect in any of the five enzymatic steps required to synthesize cortisol from cholesterol. Persistently high levels of 17-OH progesterone are considered diagnostic of CAH resulting from 21-hydroxylase deficiency. CAH exists in three forms: salt wasting (SW); simple virilising (SV); and non-classical (NC). The SW and SV forms result in excessive adrenal androgen secretion early in fetal life. If left untreated, the SW form can result in life threatening adrenal crises within the first weeks of life and precocious growth in both sexes. NC form may result in persistent slight elevations of 17-OH progesterone from birth with clinical manifestations occurring later in life.