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''Synonym: haemoglobin<BR>
'''''German''': [[:de:Hämoglobin|Hämoglobin]]'' <br>
[[de:Hämoglobin]]

==Definition==
'''Hemoglobin''' is the [[iron]]-containing red blood pigment in [[red blood cell]]s of vertebrates and its derivatives. It enables the transport of [[oxygen]] in the body.

==Biochemistry==
Hemoglobin is made up of cyclic tetrapyrrole which contains iron, an oxygen binding [[heme]] group as a [[prosthetic group]], and a protein part ([[globin]]).

One hemoglobin molecule is a [[heterotetramer]] formed by two alpha- and two other subunits that make the classification of different hemoglobins possible. The majority of [[adult]] hemoglobin contains beta chains, whereas [[fetal hemoglobin]] contains gamma chains. Delta chains have been described as well.

Each of these subunits possesses a [[prosthetic group]] which is responsible for actually binding the oxygen. As a result one hemoglobin tetramer can bind four oxygen molecules in total.

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==Physiology==
There are two variants of hemoglobin, depending on their oxygen-binding status:
* oxygenated [[oxyhemoglobin]] (OHb)
* deoxygenated [[deoxyhemoglobin]] (HHb)

Measuring hemoglobin plays an important role in the diagnosis of [[anemia]] and is done by determining the [[hemoglobin concentration]] (Hb) of a [[whole blood]] sample.

''see also:'' [[hemoglobin synthesis]], [[hemoglobin degradation]]

==Clinical chemistry==
Determining the [[hemoglobin concentration]] (Hb) is an integral part of general diagnostics. It can be used to gauge the blood's oxygen transport capacity and to diagnose [[anemia]] and [[polycythemia]].

{| table
! &nbsp; || g/dl || mmol/l
|-
| Men || 13,5–17,5	 || 8,7–11,2
|-
| Women || 12–16 || 7,5–9,9
|-
|}

Reference values for children depend on their age.

==Conversion==
<dctrinket id="ec9e61067e" type="html" height="280" />
Note: Press the "Umrechnen" button to convert between the units.

==Variants==
===HbA1c===
A high glucose concentration in the blood leads to increased non-enzymatic [[glycation]] of hemoglobin. [[HbA1c]] is the stable [[ketoamine]] which is formed by the glycation of β-hemoglobin in the second position of the [[amino acid]] [[valine]]. This reaction only takes place to a relevant extent in the case of a long-term increased glucose concentration, which is why it is used for the observation of blood sugar levels in [[diabetes]] patients.

===Dyshemoglobins===
[[Dyshemoglobin]]s are hemoglobin derivatives that cannot be oxygenated because the oxygen binding sites at the central iron atom are blocked. An example is the oxidation of the iron ion into trivalent iron which results in [[methemoglobin]] (MetHb). Methemoglobin can be converted back to the original hemoglobin by the NADH dependent [[methemoglobin reductase]]. In healthy humans less than two per cent of hemoglobin is present as methemoglobin.

Other dyhemoglobins are [[carboxyhemoglobin]] (COHb) and [[sulfhemoglobin]] (SulfHb).

==Mutations==
Modified hemoglobin variants can form due to [[mutation]] of the globin chain amino acid sequence. An example is [[hemoglobin S]] (HbSS) which occurs in patients with [[sickle-cell anemia]]
[[Tag:Biochemistry]]
[[Tag:Blood]]
[[Tag:Blood count]]
[[Tag:General medicine]]
[[Tag:Hemogram]]
[[Tag:Physiology]]
[[Tag:Pigment]]
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