Hemoglobin is the protein in red blood cells that carries oxygen from the lungs to the tissues and takes carbon dioxide back. In essence, it is the oxygen transport in your body.
When hemoglobin is low, anemia develops: the tissues get too little oxygen, hence the fatigue, pallor and shortness of breath. The most common cause of low hemoglobin is iron deficiency.
Reference ranges
Approximate reference:
| Men | 130 – 170 g/L |
| Women | 120 – 150 g/L |
| Anemia — if | below the lower limit |
What an elevated level means
A high hemoglobin is less common. Causes:
Relative: dehydration (the blood "thickens"), and then hemoglobin is falsely high.
True: living at altitude, smoking, chronic lung and heart disease (the body compensates for a lack of oxygen), less often — blood diseases.
A persistently high hemoglobin with no obvious cause warrants evaluation by a doctor.
What a low level means
A low hemoglobin (anemia) shows up as fatigue, weakness, pallor, breathlessness on exertion, and sometimes cravings for unusual tastes and brittle nails.
Causes: iron deficiency (the most common), vitamin B12 or folate deficiency, blood loss (including hidden), chronic diseases.
Do not raise hemoglobin "blindly" with iron — first find the cause and check ferritin.
How the test is done
Blood from a finger or vein as part of a complete blood count. It needs no special preparation, but it is best tested fasting in the morning.
If hemoglobin is low, be sure to check ferritin (iron stores), and if needed vitamin B12 and folate.
What affects the value
- Iron stores (ferritin) — the main factor; their depletion leads to anemia.
- Vitamin B12 and folate — needed to form red blood cells.
- Blood loss — heavy periods, hidden GI bleeding.
- Hydration — dehydration falsely raises hemoglobin.
- Altitude and smoking — raise the true level.
Calculate using this marker
Calculators where Hemoglobin is used directly:
Frequently asked questions
Is a low hemoglobin always iron deficiency?
Most often yes, but not always. The cause can be a deficiency of vitamin B12 or folate, hidden blood loss, or chronic disease. That is why, in anemia, ferritin (iron stores) and other markers are checked if needed — finding the cause matters.
How do I raise hemoglobin?
It depends on the cause. With iron deficiency — iron supplements (as prescribed) and iron-rich foods; in parallel, the source of losses must be addressed. Raising hemoglobin without identifying the cause is not advisable.
Why is the norm lower in women?
Because of regular menstrual blood loss and, in general, lower muscle mass. So the lower limit of normal hemoglobin in women (120 g/L) is lower than in men (130 g/L).