Editing Anemia (section)

===Definitions===
There are a number of definitions of anemia; [[review article|reviews]] provide comparison and contrast of them.<ref name="pmid_16189263">{{cite journal | vauthors = Beutler E, Waalen J | title = The definition of anemia: what is the lower limit of normal of the blood hemoglobin concentration? | journal = Blood | volume = 107 | issue = 5 | pages = 1747–1750 | date = March 2006 | pmid = 16189263 | pmc = 1895695 | doi = 10.1182/blood-2005-07-3046 }}</ref> A strict but broad definition is an absolute decrease in red blood cell mass,<ref>{{EMedicine|article|198475|Anemia}}</ref> however, a broader definition is a lowered ability of the blood to carry [[oxygen]].<ref name="Ber2007">{{cite book|last=Rodak|first=Bernadette F.|url=https://books.google.com/books?id=6sfacydDNsUC&pg=PA220|title=Hematology: Clinical Principles and Applications|date=2007|publisher=Saunders|isbn=978-1-4160-3006-5|edition=3rd|location=Philadelphia|page=220|archive-url=https://web.archive.org/web/20160425061405/https://books.google.com/books?id=6sfacydDNsUC&pg=PA220|archive-date=2016-04-25|url-status=live}}</ref> An [[operational definition]] is a decrease in whole-blood [[hemoglobin]] concentration of more than 2 [[standard deviation]]s below the [[mean]] of an age- and sex-matched [[Reference ranges for blood tests#Hematology|reference range]].<ref name="PDMS2">{{cite book | first1 = Albert J. | last1 = Pomeranz | first2 = Svapna | last2 = Sabnis | first3 = Sharon | last3 = Busey | first4 = Robert M. | last4 = Kliegman |year=2016 |title=Pediatric Decision-Making Strategies |edition=2nd |publisher=Elsevier |isbn=978-0-323-29854-4 }}</ref>

It is difficult to directly measure RBC mass,<ref>{{cite book|last1=Polin|first1=Richard A.|last2=Abman|first2=Steven H.|last3=Rowitch|first3=David|last4=Benitz|first4=William E. | title = Fetal and Neonatal Physiology|date=2016|publisher=Elsevier Health Sciences|isbn=978-0-323-35232-1 |page=1085|edition=5|url=https://books.google.com/books?id=JootDAAAQBAJ&pg=PA1085|url-status = live|archive-url=https://web.archive.org/web/20161031150823/https://books.google.com/books?id=JootDAAAQBAJ&pg=PA1085|archive-date=2016-10-31}}</ref> so the [[hematocrit]] (amount of RBCs) or the hemoglobin (Hb) in the [[blood]] are often used instead to indirectly estimate the value.<ref>{{cite book|last1=Uthman|first1=Ed |title=Understanding Anemia|date=2009|publisher=Univ. Press of Mississippi|isbn=978-1-60473-701-1|page=23|url=https://books.google.com/books?id=2yBl75DJ8_kC&pg=PA23 |url-status = live|archive-url=https://web.archive.org/web/20161031150408/https://books.google.com/books?id=2yBl75DJ8_kC&pg=PA23|archive-date=2016-10-31}}</ref> Hematocrit; however, is concentration dependent and is therefore not completely accurate. For example, during pregnancy a woman's RBC mass is normal but because of an increase in blood volume the hemoglobin and hematocrit are diluted and thus decreased. Another example would be bleeding where the RBC mass would decrease but the concentrations of hemoglobin and hematocrit initially remains normal until fluids shift from other areas of the body to the intravascular space.{{citation needed|date=November 2021}}

The anemia is also classified by severity into mild (110 g/L to normal), moderate (80 g/L to 110 g/L), and severe anemia (less than 80 g/L) in adults.<ref name=WHODefSeverity>{{cite book |title=Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity |date=2011 |publisher=World Health Organization |hdl=10665/85839 |hdl-access=free |last1=Organization |first1=World Health }}</ref> Different values are used in pregnancy and children.<ref name=WHODefSeverity/>