What is biochemical testing?
Biochemical testing looks at the levels of specific substances and enzymes that are produced by chemical reactions in the body.
Metabolic disorders are often the result of a missing or non-functional enzyme. When an enzyme is missing, greatly reduced in quantity, or is not working properly, the body cannot perform its usual chemical reactions.
As a result, several harmful changes in body biochemistry can occur. These include accumulation of substrate, accumulation of precursors, deficiency of products, redirection of substrate into alternate pathways.
Biochemical testing looks at the levels of these disturbances and can be used to detect several different metabolic conditions.
What disorders does PerkinElmer Genetics detect with biochemical testing?
Biotinidase deficiency is caused by mutations in the biotinidase gene resulting in loss of enzyme function. PerkinElmer Genetics uses an automated assay to quantitate biotinidase activity. Samples with low activity are further analyzed by a second tier DNA testing for common mutations to confirm the deficiency (See DNA Screening for details).
Congenital Adrenal Hyperplasia (CAH):
CAH is caused by a deficiency of the enzyme 21-hydroxylase. When this enzyme is deficient or inactive, the precursor 17-hydroxyprogesterone (17-OHP) accumulates. PerkinElmer Genetics utilizes an ELISA method to detect the amount of 17-OHP molecules present. We also perform an extracted assay that reduces the amount of interfering substances in the blood for more accurate measurement of 17-OHP. This extracted method reduces the number of false positive screening results. Together, our screening identifies both the salt-wasting and simple virilizing forms of CAH. In the near future, DNA analysis for common CAH gene mutations will also be performed when warranted.
Cystic fibrosis is characterized by severe respiratory problems and pancreatic enzyme deficiencies. As a result of the pancreatic problems, children with cystic fibrosis often have a high blood level of immuno-reactive trypsinogen (IRT). PerkinElmer Genetics uses an ELISA method to measure the level of IRT. Because an increased level of IRT can be caused by situations other than CF, PerkinElmer Genetics employs a second tier of screening by testing for 43 mutations and polymorphisms of the Cystic Fibrosis gene. (See DNA Screening for details). This second tier testing will increase accuracy in disorder detection.
Galactosemia is caused by a deficiency of one of several enzymes needed to process the milk sugar called lactose. When a baby with galactosemia ingests milk products, another sugar called galactose accumulates in the blood. The classical form of the condition results from a deficiency of the enzyme galactose-1-phosphate uridyltransferase (GALT). Other forms of galactosemia are caused by deficiencies of other enzymes such as galactokinase and epimerase. PerkinElmer Genetics uses fluorometric methods to measure the level of total galactose as well as the level of GALT activity. Based upon these results, testing for a modified galactose level and DNA analysis for the three most common galactosemia mutations may be performed. (See DNA Screening for details). Together, these methods provide the most comprehensive screening for galactosemia and significantly reduce the number of false negative screening results.
Congenital Hypothyroidism (CH):
Congenital Hypothyroidism is caused by abnormally low circulating thyroxin, which then triggers increased production of thyroid stimulating hormone (TSH). At PerkinElmer Genetics, we measure TSH in blood spots with an ELISA method to detect CH.
Are There Any Special Considerations for Biochemical Testing?
Since several of our biochemical screening methods rely on measurement of the level of enzyme activity or function, it is important that blood samples for testing be protected from exposure to excessive heat and humidity. Such exposure can be harmful to the blood specimen and may cause certain enzymes to degrade. If a sample is exposed to high temperatures and high humidity, the potential enzyme degradation may lead to false positive test results. PerkinElmer Genetics has a mechanism to identify samples with obvious exposure to excessive conditions and will classify them as unacceptable for testing. Sample with less obvious exposure may not be classified as such.