The newborn heel prick test (Guthrie test) is a term used to describe the newborn blood spot screening test that is offered to all newborns at the age of 5-40 days. It is designed to screen the baby for between 9 and 26 rare but potentially lethal diseases, which could lead to unexpected early and serious sickness in children and even developmental problems in many cases.
Early detection and treatment of these conditions, before any symptoms arise, can help to prevent severe and permanent disability, as well as avert lethal consequences. Appropriate management may include medication, dietary therapy, and physical or occupational therapy. This is the reason underlying the institution of the heel prick test in newborns.
Screening refers to the process of detecting the possibility of developing a disease in a person who currently appears to be healthy but has a risk of the condition. The tests employed are usually very sensitive but may not be equally specific. This means that the tests pick up possible markers of the disease or condition very well but may not always rule out false indicators produced by other conditions.
The procedure is simple, involving the collection of just a few drops of blood from the baby’s heel on a special card. The conditions screened for include:
- Hemoglobinopathies such as sickle cell disease
- Cystic fibrosis
- Inborn errors of metabolism involving fatty acid, carbohydrate and amino acid metabolism, including galactosemia and phenylketonuria
- Congenital adrenal hyperplasia
- Congenital hypothyroidism
- Infections such as human immunodeficiency disease (HIV) and toxoplasmosis
Any family or personal history of these conditions should be revealed to the healthcare provider beforehand.
Is the heel prick test mandatory?
In many states of the US this type of testing is mandatory, but not in many other countries. It is highly recommended, however, because it is potentially life-saving. It is not necessary to have the infant screened for all the conditions. If preferred, one can choose only the inherited metabolic diseases for screening.
The heel prick test can be done at any point up to 12 months of age. Cystic fibrosis is the only exception, because it can be screened for only up to 8 weeks of age after which it is not reliable.
Results of the heel prick test
The results are usually available within 6-8 weeks. The results are entered in the child’s medical records, which should be preserved for all future visits. If the child is reported to be positive for any screening test, earlier intimations will be made for the purpose of follow-up or specialized confirmatory testing. In some cases, cystic fibrosis or sickle cell disease testing is positive in babies who are carriers of the genetic defect but not affected by it.
Normal results imply a very low likelihood of having the disease tested for. However, these tests are not absolutely certain, and so the possibility of a false result is always present even if the screening result is negative – called a false negative. The converse may also occur, and is called a false positive.
Reviewed by Afsaneh Khetrapal BSc (Hons)