How Do They Define Anemia?

[Llenroc]

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Is anemia low red blood cell content? Is it low hemoglobin? Is it low O2 dissolved in blood? How exactly do they define it? 😕

 

[glorytaker]

Defined as: Hb of < 12 g/dl or Hct < 36% in women and Hb < 14g/dl or HCT <41% in men.

 

[BaylorGuy]

Anemia mainly only deals with Hgb and Hct

 

[leviathan]

Is anemia low red blood cell content? Is it low hemoglobin? Is it low O2 dissolved in blood? How exactly do they define it? 😕

Tissue delivery of oxygen (DO2) is a product of Hb concentration, Hb O2 saturation, cardiac output, and minimally related to O2 plasma concentration. Anemia is impaired DO2 due to a decrease in [Hb] concentration. If you have a low RBC content (as you asked), as a result of a low Fe level, hemorrhage, B12 deficiency, hemolysis, or if you have a direct reduction in Hb due to one of the various hemoglobinopathies....or anything that could cause anemia, the end result is low Hb, so that is why it is a useful biochemical and diagnostic marker for anemia.

You also asked if it was low O2 dissolved in blood, but this is a very, very minute contributor to the delivery of oxygen to tissues and is insignificant for the most part. More importantly, it does not cause anemia. If I can go off on a tangent for a second, it might be useful for you to know that plasma diffusion of O2 CAN have a much more significant effect in oxygen delivery in cases of anemia, and it can actually increase the DO2 in a shocky patient by as much as 10% if you increase the PO2 to a high enough level. This can of course be obtained by using a mask that can give 100% FiO2 like a non-rebreather.

Anyone reading this, correct me if I'm wrong here as I am a pre-med student but I'm pretty sure this would be an accurate description. If you can understand the general pathophysiology behind anemia, you won't have trouble remembering in the future that it is Hb or Hct which defines anemia.

 

[DropkickMurphy]

Low O2 in the blood is hypoxemia, not anemia.

 

[DropkickMurphy]

Tissue delivery of oxygen (DO2) is a product of Hb concentration, Hb O2 saturation, cardiac output, and minimally related to O2 plasma concentration. Anemia is impaired DO2 due to a decrease in [Hb] concentration. If you have a low RBC content (as you asked), or a low Fe level, hemorrhage, B12 deficiency, hemolysis, or anything that could cause anemia, the end result is low Hb, so that is why it is a useful biochemical and diagnostic marker for anemia.

You also asked if it was low O2 dissolved in blood, but this is a very, very minute contributor to the delivery of oxygen to tissues and is insignificant for the most part. More importantly, it does not cause anemia. If I can go off on a tangent for a second, it might be useful for you to know that plasma diffusion of O2 CAN have a much more significant effect in oxygen delivery in cases of anemia, and it can actually increase the DO2 in a shocky patient by as much as 10% if you increase the PO2 to a high enough level. This can of course be obtained by using a mask that can give 100% FiO2 like a non-rebreather.

Correct me if I'm wrong here as I'm a pre-med student but I'm pretty sure this would be an accurate description. If you can understand the general pathophysiology behind anemia, you won't have trouble remembering in the future that it is Hb or Hct which defines anemia.

Uh, you can't give 100% O2 with an NRB. Due to the leaks inherent with that system the highest you are likely to achieve is 80% (maybe 90% on a very good day).

 

[leviathan]

Uh, you can't give 100% O2 with an NRB. Due to the leaks inherent with that system the highest you are likely to achieve is 80% (maybe 90% on a very good day).

Yes, very good point Praetorian. Theoretically, you could give 100% O2 if it wasn't for the inherent leaks, however the fact of the matter still is you can increase PO2 to high enough levels to increase DO2 by as much as 10%.

 

[robotsonic]

Is anemia low red blood cell content? Is it low hemoglobin? Is it low O2 dissolved in blood? How exactly do they define it? 😕

Do people not use textbooks anymore?

 

[leviathan]

Do people not use textbooks anymore?

I'm guessing he is a first year med student or something.

 

[DropkickMurphy]

Only if the problem is truly a pure oxygenation issue and not an matter of ventilation or delivery.

 

[leviathan]

Only if the problem is truly a pure oxygenation issue and not an matter of ventilation or delivery.

If you were referring to my post, then yes, I was making the 10% claim under the assumption that cardiac output and oxygen saturation are normal. 👍