Editing Pregnancy test (section)

==Accuracy==
[[File:Negative_Pregnancy_Test.JPG|thumb|200x200px|The control line of this pregnancy test is blank, making the test invalid.]]
[[File:PositivePregnancyTest.JPG|alt=|thumb|200x200px|The control line on the left of this pregnancy test is visible, suggesting that the test result is valid. A pale purple line has also appeared on the right hand side (the test line) which clearly signifies that the subject is pregnant.]]
A systematic review published in 1998 showed that home pregnancy test kits, when used by experienced technicians, are almost as accurate as professional laboratory testing (97.4%). When used by consumers, however, the accuracy fell to 75%: the review authors noted that many users misunderstood or failed to follow the instructions included in the kits.<ref>{{cite journal|vauthors=Bastian LA, Nanda K, Hasselblad V, Simel DL|year=1998|title=Diagnostic efficiency of home pregnancy test kits. A meta-analysis|url=http://archfami.ama-assn.org/cgi/pmidlookup?view=long&pmid=9755740|journal=Arch Fam Med|volume=7|issue=5|pages=465–9|doi=10.1001/archfami.7.5.465|pmid=9755740|archive-url=https://archive.today/20081206110632/http://archfami.ama-assn.org/cgi/pmidlookup?view=long&pmid=9755740|archive-date=6 December 2008|access-date=12 May 2008}}</ref>

=== False positive ===
[[Type I and type II errors|False positive]] pregnancy test results are rare and may occur for several reasons, including:

* user error in performing and interpreting the test,
* biochemical pregnancy (loss of pregnancy before signs of pregnancy are apparent on ultrasound, likely very soon after implantation),
* and non-pregnant production of the hCG molecule (i.e. secretion due to a tumor or the pituitary gland, some diseases of the [[liver]], [[cancer]]s, including [[choriocarcinoma]] and other [[germ cell tumor]]s, [[Selective immunoglobulin A deficiency|IgA deficiencies]], [[Heterophile|heterophile antibodies]], enterocystoplasties, [[gestational trophoblastic disease]]s (GTD), and gestational [[trophoblastic neoplasm]]s).<ref name="ReferenceA2">{{cite journal|last1=Stenman|first1=Ulf-Håkan|last2=Alfthan|first2=Henrik|last3=Hotakainen|first3=Kristina|date=July 2004|title=Human chorionic gonadotropin in cancer|journal=Clinical Biochemistry|volume=37|issue=7|pages=549–561|doi=10.1016/j.clinbiochem.2004.05.008|pmid=15234236}}</ref><ref name=":02" />
* bacterial contamination and blood in urine<ref name="Wallach 2007 https://archive.org/details/interpretationof0000wall_t4n7/page/866 866">{{cite book|last=Wallach|first=Jacques|url=https://archive.org/details/interpretationof0000wall_t4n7|title=Interpretation of diagnostic tests|publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins|year=2007|isbn=978-0-7817-3055-6|edition=8th|location=Philadelphia|page=[https://archive.org/details/interpretationof0000wall_t4n7/page/866 866]|url-access=registration}}</ref>

Spurious ''evaporation lines'' may appear on many home pregnancy tests if read after the suggested 3–5 minute window or reaction time, independent of an actual pregnancy. False positives may also appear on tests used past their expiration date.<ref>{{Cite web|title=First Response early result pregnancy test|url=https://www.firstresponse.com/en/product-listings/-/media/81865E866A764C1CAB5B7B340B8E7F60.ashx#.pdf|website=FirstResponse.com}}</ref>

====Due to use of medication====
Urine tests can be falsely positive in those that are taking the medications: [[chlorpromazine]], [[promethazine]], [[phenothiazines]], [[methadone]],<ref name="Wallach 2007 https://archive.org/details/interpretationof0000wall_t4n7/page/866 866"/> [[aspirin]], [[carbamazepine]] and drugs that cause high urinary pH.<ref name=statsp>{{cite journal | vauthors = Betz D, Fane K | title = Human Chorionic Gonadotropin | journal = Statpearls| date = 2020 | pmid = 30422545}}[[File:CC-BY icon.svg|50px]] Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>

=== False negative ===
[[Type I and type II errors|False negative]] readings can occur when testing is done too early. hCG levels rise rapidly in early pregnancy and the chances of false negative test results diminish with time (increasing [[Gestational age (obstetrics)|gestational age]]).<ref name="wilcox2">{{cite journal|vauthors=Wilcox AJ, Baird DD, [[Clarice Weinberg|Weinberg CR]]|year=1999|title=Time of implantation of the conceptus and loss of pregnancy|journal=New England Journal of Medicine|volume=340|issue=23|pages=1796–1799|doi=10.1056/NEJM199906103402304|pmid=10362823|doi-access=free}}</ref> Less sensitive urine tests and qualitative blood tests may not detect pregnancy until three or four days after implantation.<ref>{{cite journal|vauthors=Wilcox AJ, Baird DD, Weinberg CR|date=June 1999|title=Time of implantation of the conceptus and loss of pregnancy|journal=New England Journal of Medicine|volume=340|issue=23|pages=1796–9|doi=10.1056/NEJM199906103402304|pmid=10362823|doi-access=free}}</ref> [[Menstruation]] occurs on average 14 days after ovulation, so the likelihood of a false negative is low once a menstrual period is late. Ovulation may not occur at a predictable time in the [[menstrual cycle]]. A number of factors may cause an unexpectedly early or late ovulation, even for people with a history of regular menstrual cycles.<ref>{{Cite journal|last=Chard|first=T.|date=May 1992|title=Pregnancy tests: a review|journal=Human Reproduction (Oxford, England)|volume=7|issue=5|pages=701–710|doi=10.1093/oxfordjournals.humrep.a137722|issn=0268-1161|pmid=1639991}}</ref> Medical providers often struggle to 'rule out' pregnancy for medical testing or treatment that cannot be conducted during pregnancy before they can do an accurate urine pregnancy test.<ref>{{cite journal |last1=Brown |first1=Eliza |date=2020 |title=Projected diagnosis, anticipatory medicine, and uncertainty: How medical providers 'rule out' potential pregnancy in contraceptive counseling |journal=Social Science & Medicine |volume=258 |pages=113–118 |doi=10.1016/j.socscimed.2020.113118 |doi-access=free |pmid=32569949 }}</ref> 

More rare, false negative results can also occur due to a "[[hook effect]]", where a sample with a very high level of hCG is tested without dilution, causing an invalid result.<ref>{{Cite journal|last1=Griffey|first1=Richard T.|last2=Trent|first2=Caleb J.|last3=Bavolek|first3=Rebecca A.|last4=Keeperman|first4=Jacob B.|last5=Sampson|first5=Christopher|last6=Poirier|first6=Robert F.|date=January 2013|title="Hook-like effect" causes false-negative point-of-care urine pregnancy testing in emergency patients|journal=The Journal of Emergency Medicine|volume=44|issue=1|pages=155–160|doi=10.1016/j.jemermed.2011.05.032|issn=0736-4679|pmid=21835572|doi-access=free}}</ref>