Parents - Expanded Newborn Screening

Expanded newborn screening uses a new technology called tandem mass spectrometry (MS/MS) to screen newborns for over thirty disorders. Only a few drops of the baby's blood are needed to do this expanded newborn screening test. Many people are excited about expanded newborn screening because it can screen a baby for many disorders without needing more blood collected than for the current newborn screening test. Expanded newborn screening is also fast, accurate, and cheap.

While expanded newborn screening using MS/MS is relatively new, tandem mass spectrometry technology has been used for many years. Scientists have used MS/MS technology to measure all kinds of different substances. For example, MS/MS technology is used in drug tests to determine what type of drug a person has taken.

In the past, this technology was time-consuming and expensive. Both of these factors (time and cost) made MS/MS impractical for newborn screening. Newborn screening requires a large number of tests to be done quickly, accurately and inexpensively. It was only after MS/MS became automated (done with the help of computers) that it became possible to use this technology in newborn screening. Computers allowed MS/MS to be quick, accurate and relatively inexpensive.

How does MS/MS work?

MS/MS works by separating and measuring substances according to their weight. When a drop of a newborn's blood is placed in the MS/MS machine, a special chamber in the machine causes all the substances in the blood to separate and move. The smaller, lighter substances move faster than the larger, heavier substances. The substances move across a special filter and a computer records which substances are present. In addition to recording which substances are present, the computer also measures the quantity of a particular substance. For example, in the picture below, a blood spot is put through the MS/MS machine and the results show that there are three substances - A, B, and C - and that there is twice as much of substance B as there is of A and C.

 How does MSMS work

MS/MS is a very precise and sensitive technique. While the example above is relatively simple, expanded newborn screening using MS/MS is more complex.  

How is MS/MS used in expanded newborn screening?

Expanded newborn screening by MS/MS identifies and measures two different groups of substances - acylcarnitines and amino acids. About 24 to 72 hours after a baby is born, a few drops of blood are taken from the baby's heel and dabbed on a special type of filter paper. The filter paper is mailed to a newborn screening laboratory which will perform all of the newborn screening tests.

Using MS/MS, the lab will measure which acylcarnitines and amino acids are present in the newborn's blood. It will also measure how much of each substance is present in the newborn's blood. In this way, MS/MS can be used to screen for over thirty different rare inherited metabolic disorders. Everyone has acylcarnitines and amino acids in their blood. However, infants with rare inherited metabolic disorders have either too much or not enough amino acids and acylcarnitines. They can also have unusual types of amino acids and acylcarnitines in their blood.

If my baby has an abnormal result, do they have a disorder?

It is important to remember that the expanded newborn screening test does not diagnose infants with disorders. The screening test simply picks out which infants may be more likely to have one of these disorders. If an infant has an abnormal screening test result, additional tests MUST be done to confirm whether or not the infant really has the disorder. Any infant with an abnormal MS/MS newborn screening test will be referred to a specialist for further testing. Because MS/MS is such a sensitive technique, there can be lots of reasons for small abnormalities that can lead to an abnormal test result in a healthy baby (this is called a "false positive" test result). However, every infant with an abnormal screening test result needs to have follow-up testing.

All in all, MS/MS is a very precise testing method that is used to screen newborns for over thirty rare inherited metabolic disorders by identifying and measuring the amounts of acylcarnitines and amino acids in their blood. Early identification and treatment of these infants will allow them to lead healthier lives.  


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This project is supported by a grant from the Maternal and Child Health Bureau,
Health Resources and Service Administration, Genetic Services Branch,
MCH Project #:1H46 MC 00189-03