Reasons for Guthrie blood test?

April 1, 2010

A Guthrie blood test, which is also known as the Guthrie bacterial inhibition assay, is one of the most important medical tests performed on newborn babies. This test is carried out to detect the presence of phenylketonuria in infants. Phenylketonuria is a medical condition that can affect a person’s ability, to metabolize phenylalanine, which is a type of an amino acid. Incase the levels of phenylalanine build up, due to improper metabolism; it can lead to a serious medical handicap. If phenylketonuria is detected soon after the baby is born, measures can be taken to prevent any intellectual disabilities or other side effects. To minimize the effect of this condition, all you need to do is follow a low-protein diet, which restricts exposure to phenylalanine. To conduct this test, a sample of blood is taken from the baby’s heel, on the sixth or the seventh day, after birth. If the blood sample is taken too early, the reading may not be accurate.

After collecting the blood, the sample is incubated with a genus of bacteria known as Bacillus subtilis, along with a chemical, known as B-2-phenylalanine. This chemical tries to inhibit the growth of the bacteria, by preventing them from feeding of the phenylalanine present in the sample. If the bacteria cannot grow, the result is negative. If the bacteria can grow in the sample, the result is positive, which indicates the presence of phenylketonuria in the infant. Further tests may then need to be conducted, to check why the levels of phenylalanine are elevated.

Apart from the detection of phenylketonuria, the blood sample taken from the baby’s heel for the Guthrie blood test is also analyzed for the following conditions:

  • Congenital hypothyroidism: This condition indicates the deficiency of a growth hormone, called thyroxin. A person cannot grow normally, without the thyroxin hormone. Therefore, the condition needs to be treated as early as possible, using growth hormone supplements.
  • Sickle cell disease: This condition changes the shape of the red blood cells and causes a reduction in their ability of carrying oxygen to all parts of the body.
  • Cystic Fibrosis: This condition affects a person’s digestive system and lungs. It is normally an inherited problem.
  • MCAD Deficiency: This condition impairs the proper metabolism of fat in the body. Its effects can be minimized by an alteration in the diet.

All these conditions can be treated to some extent, which is why it is important to screen for them as early as possible.

Submitted by M T on April 1, 2010 at 06:07

Read more questions in Blood Tests