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==Interpretation==
A [[reference range]] is usually defined as the set of values 95 percent of the normal population falls within (that is, 95% [[prediction interval]]).<ref>[{{Cite book |url=https://books.google.com/books?id=Je_pJfb2r0cC&pg=PA19 Page 19] in: {{cite book |author=Stephen K. Bangert MA MB BChir MSc MBA FRCPath; William J. Marshall MA MSc MBBS FRCP FRCPath FRCPEdin FIBiol; Marshall, William Leonard |title=Clinical biochemistry: metabolic and clinical aspects |publisher=Churchill Livingstone/Elsevier |___location=Philadelphia |year=2008 |isbn=978-0-443-10186-1 |editor-last=Bangert |editor-first=Stephen K. |edition=2nd |___location=Philadelphia |page=19 |editor-last2=Marshall |editor-first2=William J.}}</ref> It is determined by collecting data from vast numbers of laboratory tests.<ref>{{citeCite journal |last1last=Boyd |first1first=James C. |date=January 2010 |title=Defining laboratory reference values and decision limits: populations, intervals, and interpretations |journal=Asian Journal of Andrology |date=January 2010 |volume=12 |issue=1 |pages=83–90 |doi=10.1038/aja.2009.9 |pmidissn=201110861745-7262 |pmc=3739683 |issnpmid=1745-726220111086}}</ref><ref>{{citeCite web |title=Reference Ranges & What They Mean {{!}} Lab Tests Online-UK |url=https://labtestsonline.org.uk/articles/laboratory-test-reference-ranges |website=labtestsonline.org.ukLab Tests Online-UK}}</ref>
===Plasma or whole blood===
In this article, all values (except the ones listed below) denote [[blood plasma]] concentration, which is approximately 60–100% larger than the actual blood concentration if the amount inside [[red blood cells]] (RBCs) is negligible. The precise factor depends on [[hematocrit]] as well as amount inside RBCs. Exceptions are mainly those values that denote total blood concentration, and in this article they are:<ref name="pmid33274357">{{citeCite journal| author|vauthors=Bransky A, Larsson A, Aardal E, Ben-Yosef Y, Christenson RH |year=2021 |title=A Novel Approach to Hematology Testing at the Point of Care. | journal=J Appl Lab Med | year= 2021 | volume= 6 | issue= 2 | pages= 532–542 | pmid=33274357 | doi=10.1093/jalm/jfaa186 | pmc=7798949 |pmid=33274357}} </ref>
* All values in ''Hematology – red blood cells'' (except ''hemoglobin in plasma'')
* All values in ''Hematology – white blood cells''
===Units===
* [[Mass concentration (chemistry)|Mass concentration]] (g/dL or g/L) is the most common measurement unit in the United States. Is usually given with dL (decilitres) as the denominator in the United States, and usually with L (litres) in, for example, Sweden.{{cn|date=February 2024}}
* [[Molar concentration]] (mol/L) is used to a higher degree in most of the rest of the world, including the United Kingdom and other parts of Europe and Australia and New Zealand.<ref>[{{Cite book |last=Dart |first=Richard C. |url=https://books.google.com/books?id=BfdighlyGiwC "Units|title=Medical oftoxicology measurement"]|publisher=Lippincott inWilliams ''Medical& toxicology''Wilkins |year=2004 |isbn=978-0-7817-2845-4 |edition=3, Richardillustrated C.|page=34 Dart|chapter=Units of measurement}}</ref>
Edition: 3, illustrated, Lippincott Williams & Wilkins, 2004, p. 34 {{ISBN|978-0-7817-2845-4}} 1914 pages</ref>
* [[International unit]]s (IU) are based on measured [[biological activity]] or effect, or for some substances, a specified equivalent mass.{{cn|date=February 2024}}
* [[Enzyme activity]] ([[katal|kat]]) is commonly used for e.g. [[liver function test]]s like [[Aspartate transaminase|AST]], [[Alanine transaminase|ALT]], [[lactate dehydrogenase|LD]] and [[Gamma-glutamyl transpeptidase|γ-GT]] in Sweden.<ref name=uppsala/>
* [[Percentage]]s and time-dependent units (mol/s) are used for calculated derived parameters, e.g. for [[beta cell]] function in [[Homeostatic model assessment|homeostasis model assessment]] or [[thyroid's secretory capacity]].<ref>{{citeCite journal |last1last=Hill |first1first=Nathan R. |last2=Levy |first2=Jonathan C. |last3=Matthews |first3=David R. |date=11 July 2013 |title=Expansion of the Homeostasis Model Assessment of β-Cell Function and Insulin Resistance to Enable Clinical Trial Outcome Modeling Through the Interactive Adjustment of Physiology and Treatment Effects: iHOMA2 |journal=Diabetes Care |date=11 July 2013 |volume=36 |issue=8 |pages=2324–2330 |doi=10.2337/dc12-0607 |pmid=23564921 |pmc=3714535 |url=https://diabetesjournals.org/care/article/36/8/2324/33141/Expansion-of-the-Homeostasis-Model-Assessment-of |journal=Diabetes Care |volume=36 |issue=8 |pages=2324–2330 |doi=10.2337/dc12-0607 |issn=0149-5992 |pmc=3714535 |pmid=23564921}}</ref>
===Arterial or venous===
If not otherwise specified, a reference range for a blood test is generally the [[vein|venous]] range, as the standard process of obtaining a sample is by [[venipuncture]]. An exception is for acid–base and [[blood gas]]es, which are generally given for arterial blood.<ref>{{citeCite bookweb |title=Reference Interval and Critical Results Table |url=https://pathology.vcu.edu/media/pathology/catalog/LAB.GEN.0022CPathologyBloodGasTestingandWholeBloodChemistryRefIntervalsCritValues05.17.2024.pdf |website=VCU Health Pathology |department=Blood Gas Laboratory}}</ref>
Still, the blood values are approximately equal between the arterial and venous sides for most substances, with the exception of acid–base, blood gases and drugs (used in [[therapeutic drug monitoring]] (TDM) assays).<ref name="Dufour">[{{Cite magazine |last=Dufour |first=D. Robert |date=April 2000 |title=Arterial versus venous reference ranges |url=http://findarticles.com/p/articles/mi_m3230/is_4_32/ai_61893437/ "Arterial|url-status=dead versus|archive-url=https://web.archive.org/web/20050421011421/http://findarticles.com/p/articles/mi_m3230/is_4_32/ai_61893437/ venous|archive-date=2005-04-21 reference ranges"], ''|magazine=Medical Laboratory Observer'', April, 2000 by D. Robert Dufour}}</ref> Arterial levels for drugs are generally higher than venous levels because of extraction while passing through tissues.<ref name=Dufour/>
===Usual or optimal===
===Variability===
{{Further|Reference range}}
References range may vary with age, sex, race, pregnancy,<ref>{{Cite journal |last=Abbassi-Ghanavati doi|first=M. |last2=Greer 10|first2=L.1097/AOG G.0b013e3181c2bde8| pmid |last3=Cunningham 19935037|first3=F. titleG. |year=2009 |title=Pregnancy and Laboratory Studies| |journal = Obstetrics & Gynecology| |volume =114 114| issue =6 6| pages = 1326–31| year = 2009| last1 doi= Abbassi-Ghanavati | first1 = M10. | last2 = Greer | first2 = L. G1097/AOG.0b013e3181c2bde8 | last3 pmid= Cunningham19935037 | first3 = F. G. | s2cid = 24249021}}</ref> diet, use of prescribed or herbal drugs and stress. Reference ranges often depend on the analytical method used, for reasons such as [[Accuracy and precision|inaccuracy]], lack of [[standardisation]], lack of [[certified reference materials|certified reference material]] and differing [[epitope|antibody reactivity]].<ref>{{citeCite journal |last=Armbruster |first=David |author2last2=Miller |first2=Richard R. |date=August 2007 |title=The Joint Committee for Traceability in Laboratory Medicine (JCTLM): A Global Approach to Promote the Standardisation of Clinical Laboratory Test Results |journal=The Clinical Biochemist Reviews|date=August 2007|volume=28 |issue=3 |pages=105–14 |pmc=1994110 |pmid=17909615}}</ref> Also, reference ranges may be inaccurate when the reference groups used to establish the ranges are small.<ref>{{citeCite journal |titlelast=SampleMeeker Sizes for Prediction Intervals|authorfirst=William Q. Meeker &|last2=Hahn |first2=Gerald J. Hahn|doiyear=10.1080/00224065.1982.11978821 |title=Sample Sizes for Prediction Intervals |journal=Journal of Quality Technology |volume=14|year=1982 |issue=4 |pages=201–206 |doi=10.1080/00224065.1982.11978821}}</ref>
==Sorted by concentration==
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