Editing Neonatal heel prick

{{Short description|Blood collection procedure for newborns}}
[[File:Phenylketonuria testing.jpg|thumb|The blood of a two-week-old infant is collected for a [[Phenylketonuria]], or PKU, screening]]

The '''neonatal heel prick''' is a [[blood collection|blood collection procedure]] done on [[newborn]]s. It consists of making a pinprick puncture in one [[heel]] of the newborn to collect their [[blood]]. This [[Medical procedure|technique]] is used frequently as the main way to collect blood from neonates.  Other techniques include [[vein|venous]] or [[artery|arterial]] [[needle stick]]s, [[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.<ref>[http://www.abc.net.au/catalyst/stories/s867619.htm Guthrie Cards] {{Webarchive|url=https://web.archive.org/web/20161201075845/http://www.abc.net.au/catalyst/stories/s867619.htm |date=2016-12-01 }}, ''[[Catalyst (TV program)|Catalyst]]'' ([[ABC1]]), 29 May 2003.</ref><ref name="McMillanFeigin2006">{{cite book|author1=Julia A. McMillan|author2=Ralph D. Feigin|author3=Catherine DeAngelis|author4=M. Douglas Jones|title=Oski's pediatrics: principles & practice|url=https://books.google.com/books?id=VbjFQiz8aR0C&pg=PA162|access-date=16 April 2010|date=1 April 2006|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-3894-1|pages=162–}}</ref>

The classical Guthrie test is named after [[Robert Guthrie (microbiologist)|Robert Guthrie]], an American [[bacteriologist]] and [[physician]] 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]] that can detect a wider variety of [[congenital disease]]s.

==Detected diseases==
The blood samples can be used for a variety of [[metabolic test]]s to detect [[genetic condition]]s, including:

* [[Immunoreactive trypsinogen]] to detect [[cystic fibrosis]].
* [[Maple syrup urine disease]] (MSUD or Branched Chain Ketonuria) a rare disorder where an error in [[metabolism]] inhibits the breakdown of [[amino acid]] leucine, isoleucine and valine.  It can impair brain development.
* [[Medium-chain acyl-coenzyme A dehydrogenase deficiency]] (MCADD)
* [[Phenylketonuria]], a disorder where an error in [[amino acid]] [[metabolism]] can impair brain development (PKU)
* [[Sickle-cell disease]]<ref>{{cite web |url=http://www.screening.nhs.uk/an/index.htm |title=NHS Screening antenatal and newborn |access-date=2009-02-26 |url-status=dead |archive-url=https://web.archive.org/web/20090212181713/http://www.screening.nhs.uk/an/index.htm |archive-date=2009-02-12 }}</ref>
* [[Thyroid stimulating hormone]] (TSH) or [[Thyroxin]] (T4) to detect [[congenital hypothyroidism]] and hence prevent [[cretinism]].
* [[Isovaleric acidemia]] (IVA)
* Homocystinuria (pyridoxine unresponsive) (HCU)
* 17-hydroxy-progesterone (17-OHP) to detect [[adrenogenital syndrome]], also known as [[congenital adrenal hyperplasia]]
* [[Galactosemia]]

==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.<ref name=uic>{{cite web|url=http://www.uic.edu/classes/phar/phar332/Clinical_Cases/aa%20metab%20cases/PKU%20Cases/PHE-TST001.htm |title=PHE-TST001 |work=uic.edu |url-status=dead |archive-url=https://web.archive.org/web/20130927101945/http://www.uic.edu/classes/phar/phar332/Clinical_Cases/aa%20metab%20cases/PKU%20Cases/PHE-TST001.htm |archive-date=2013-09-27 }}</ref>

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.<ref name=uic />

==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).<ref>{{cite web|url=http://newbornbloodspot.screening.nhs.uk/standards|title=Standards|work=screening.nhs.uk|access-date=2015-02-07|archive-date=2009-05-01|archive-url=https://web.archive.org/web/20090501152642/http://newbornbloodspot.screening.nhs.uk/standards|url-status=live}}</ref> [[False positive]]s and [[false negative]]s can sometimes occur when the screening tests are performed before 48 hours.<ref>{{cite web|url=http://www.health.vic.gov.au/genetics/nbs.htm |title=Newborn screening guidelines |work=health.vic.gov.au (via archive.org) |url-status=bot: unknown |archive-url=https://web.archive.org/web/20060308182225/http://www.health.vic.gov.au/genetics/nbs.htm |archive-date=2006-03-08 }}</ref>

When the [[immunoassay]] method is utilized as a screening method for quantifying [[17α-hydroxyprogesterone]] (17OHP) in dried blood spots, it exhibits a significant rate of false positive results. As per the clinical practice guideline issued by the Endocrine Society in 2018, employing [[LC-MS/MS]] to measure 17OHP and other adrenal steroid hormones (such as [[21-deoxycortisol]] and androstenedione) is recommended as a supplementary screening approach to enhance the accuracy of positive predictions.<ref name="pmid38169194">{{cite journal |vauthors=Mu D, Sun D, Qian X, Ma X, Qiu L, Cheng X, Yu S |title=Steroid profiling in adrenal disease |journal=Clin Chim Acta |volume=553 |issue= |pages=117749 |date=December 2023 |pmid=38169194 |doi=10.1016/j.cca.2023.117749 |url=}}</ref>

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.{{citation needed|date=June 2020}}

==Data retention controversy==
In [[Ireland]], a [[controversy]] emerged in [[2012]] whereby a number of [[hospital]]s retained heel prick test cards and thereby a [[DNA database]] with over a million samples from [[1984]], without [[consent]] or [[Parental notification|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 [[U.S. state|states]] of the [[United States]].<ref>{{cite web|url=http://www.irishtimes.com/news/international-standards-for-storing-samples-vary-wildly-1.474167|title=International standards for storing samples vary wildly|work=Irish Times|access-date=2015-03-25|archive-date=2015-04-02|archive-url=https://web.archive.org/web/20150402104723/http://www.irishtimes.com/news/international-standards-for-storing-samples-vary-wildly-1.474167|url-status=live}}</ref>

==Heel stick wound==
Heel stick [[wound]]s are a [[cutaneous condition]] characterized by a break in the skin caused by neonatal heel prick.<ref name="Bolognia">{{cite book |author=Rapini, Ronald P. |author2=Bolognia, Jean L. |author3=Jorizzo, Joseph L. |title=Dermatology: 2-Volume Set |publisher=Mosby |location=St. Louis |year=2007 |isbn=978-1-4160-2999-1 }}</ref> The heel stick is an important medical screening for the child and causes [[Pain scale|low levels of pain]].<ref>{{cite book|last1=Perry|first1=Shannon E.|title=Maternal Child Nursing Care in Canada - E-Book|date=2016|publisher=Elsevier Health Sciences|isbn=9781771720830|page=700|url=https://books.google.com/books?id=qtcoDwAAQBAJ&q=Heel+stick+wound|access-date=18 January 2018|language=en}}</ref> 

== See also ==<!-- PLEASE RESPECT ALPHABETICAL ORDER -->
* [[Dried blood spot testing]]
* [[Galactosemia]]
* [[Hyperphenylalaninemia]]
* [[Newborn screening]]

==References==
{{reflist}}

==External links==
* [http://www.gpnotebook.co.uk/simplepage.cfm?ID=x20060628142653816440 Heel prick test] at the General Practice Notebook

{{Tests relating to nutrition}}

[[Category:Midwifery]]
[[Category:Neonatology]]