The neonatal heel prick is a blood collection procedure done on newborns. It consists of making a pinprick puncture in one heel of the newborn to collect their blood. This technique is used frequently as the main way to collect blood from neonates. Other techniques include venous or arterial needle sticks, cord blood sampling, or umbilical line collection. This technique is often utilized for the Guthrie test, where it is used to soak the blood into pre-printed collection cards known as Guthrie cards. The classical Guthrie test is named after

Robert Guthrie Robert Guthrie, MD, Ph.D. (June 28, 1916 – June 24, 1995) was an American microbiologist, best known for developing the bacterial inhibition assay used to screen infants for phenylketonuria at birth, before the development of irreversible n ...

, an American

bacteriologist A bacteriologist is a microbiologist, or similarly trained professional, in bacteriology -- a subdivision of microbiology that studies bacteria, typically pathogenic ones. Bacteriologists are interested in studying and learning about bacteria, ...

and

physician A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...

who devised it in 1962. The test has been widely used throughout North America and Europe as one of the core newborn screening tests since the late 1960s. The test was initially a bacterial inhibition assay, but is gradually being replaced in many areas by newer techniques such as

tandem mass spectrometry Tandem mass spectrometry, also known as MS/MS or MS2, is a technique in instrumental analysis where two or more mass analyzers are coupled together using an additional reaction step to increase their abilities to analyse chemical samples. A com ...

that can detect a wider variety of

congenital disease A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can r ...

Detected diseases

The blood samples can be used for a variety of metabolic tests to detect genetic conditions, including: *

Immunoreactive trypsinogen Measurement of immunoreactive trypsinogen (IRT) in blood of newborn babies is an assay in rapidly increasing use as a screening test for cystic fibrosis (CF). In CF, there is poor release from pancreatic ducts. Trypsinogen is a pancreatic enzyme pr ...

to detect cystic fibrosis. *

Maple syrup urine disease Maple syrup urine disease (MSUD) is an autosomal recessive metabolic disorder affecting branched-chain amino acids. It is one type of organic acidemia. The condition gets its name from the distinctive sweet odor of affected infants' urine and ear ...

(MSUD or Branched Chain Ketonuria) a rare disorder where an error in

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...

inhibits the breakdown of

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...

leucine, isoleucine and valine. It can impair brain development. *

Medium-chain acyl-coenzyme A dehydrogenase deficiency Medium-chain acyl-CoA dehydrogenase deficiency (MCAD deficiency or MCADD) is a disorder of fatty acid oxidation that impairs the body's ability to break down medium-chain fatty acids into acetyl-CoA. The disorder is characterized by hypoglycemia ...

(MCADD) *

Phenylketonuria Phenylketonuria (PKU) is an inborn error of metabolism that results in decreased metabolism of the amino acid phenylalanine. Untreated PKU can lead to intellectual disability, seizures, behavioral problems, and mental disorders. It may also re ...

, a disorder where an error in

can impair brain development (PKU) *

Sickle-cell disease Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia. It results in an abnormality in the oxygen-carrying protein haemoglobin found in red blo ...

Thyroid stimulating hormone Thyroid-stimulating hormone (also known as thyrotropin, thyrotropic hormone, or abbreviated TSH) is a pituitary hormone that stimulates the thyroid gland to produce thyroxine (T4), and then triiodothyronine (T3) which stimulates the metabolism of ...

(TSH) or Thyroxin (T4) to detect

congenital hypothyroidism Congenital hypothyroidism (CH) is thyroid hormone deficiency present at birth. If untreated for several months after birth, severe congenital hypothyroidism can lead to growth failure and permanent intellectual disability. Infants born with con ...

and hence prevent

cretinism Congenital iodine deficiency syndrome is a medical condition present at birth marked by impaired physical and mental development, due to insufficient thyroid hormone (hypothyroidism) often caused by insufficient dietary iodine during pregnancy. It ...

. *

Isovaleric acidemia Isovaleric acidemia is a rare autosomal recessive metabolic disorder which disrupts or prevents normal metabolism of the branched-chain amino acid leucine. It is a classical type of organic acidemia. Symptoms and signs A characteristic featu ...

(IVA) * Homocystinuria (pyridoxine unresponsive) (HCU) * 17-hydroxy-progesterone (17-OHP) to detect

adrenogenital syndrome Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders characterized by impaired cortisol synthesis. It results from the deficiency of one of the five enzymes required for the synthesis of cortisol in the adrenal cortex. M ...

, also known as

congenital adrenal hyperplasia Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders characterized by impaired cortisol synthesis. It results from the deficiency of one of the five enzymes required for the synthesis of cortisol in the adrenal cort ...

Galactosemia Galactosemia (British galactosaemia, from Greek γαλακτόζη + αίμα, meaning galactose + blood, accumulation of galactose in blood) is a rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galacto ...

Mechanism

The test uses the growth of a strain of bacteria on a specially-prepared agar plate as a sign for the presence of high levels of phenylalanine, phenylpyruvate, and/or phenyllactate. The compound B-2-thienylalanine will inhibit the growth of the bacterium ''Bacillus subtilis'' (ATCC 6051) on minimal culture media. If phenylalanine, phenylpyruvate, and/or phenyllactate is added to the medium, then growth is restored. Such compounds will be present in excess in the blood or urine of patients with PKU. If a suitably-prepared sample of blood or urine is applied to the seeded agar plate, the growth of the bacteria in the test will be a positive indicator for PKU in the patient. To prepare the sample for application, a small amount of blood (from a heel puncture, for example) or urine (from a diaper, for example) is applied to a piece of filter paper. Then a small disc is punched from the center of the spot of blood or urine, and the disc applied to the surface of a seeded, minimal-medium agar plate that contains added beta-2-thienylalanine. If the sample contains phenylalanine, phenylpyruvate, and/or phenyllactate then these compounds will diffuse into the agar medium. If their concentrations are high enough (as with the excess levels seen with PKU), bacteria will grow under the disc, but not elsewhere. Generally an overnight incubation is enough to determine whether phenylalanine, phenylpyruvate, and/or phenyllactate are present in unusual concentrations in blood or urine.

Timing

The blood spot sample should be taken between 48 and 72 hours of age for all babies regardless of medical condition, milk feeding and prematurity. For the purpose of screening, date of birth is day 0 (some IT systems record date of birth as day 1).

False positive A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resul ...

s and

false negative A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resul ...

s can sometimes occur when the screening tests are performed before 48 hours. With genetic tests becoming more common, a wide variety of tests may use the blood drawn by this method. Many neonatal units (SCBUs) now use this method to carry out the daily blood tests (blood count, electrolytes) required to check the progress of ill neonates.

Data retention controversy

In Ireland, a controversy emerged in 2012 whereby a number of hospitals retained heel prick test cards and thereby a DNA database with over a million samples from 1984, without consent or notification of parents. This resulted in a ten-year rolling destruction cycle being introduced. Similar practices exist in the United Kingdom, New Zealand, and several states of the United States.

References

External links