What Causes High or Low Hemoglobin Levels?

Many different conditions can cause hemoglobin abnormalities

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Maintaining normal hemoglobin levels is important, as this blood protein carries oxygen to your cells. In males, a healthy hemoglobin level is between 13.2 and 16.6 grams per deciliter of blood (g/dL). In females, a hemoglobin count of between 11.6 and 15 g/dL is considered normal and healthy.

A lower-than-normal hemoglobin count means that your cells are not getting enough oxygen from your blood. Without ample oxygen, cells cannot convert glucose (the body's main fuel source) into energy, leading fatigue, weakness, and other signs of anemia.

By contrast, a high-than-normal hemoglobin count means that your body is being deprived of oxygen due to conditions like smoking, living at high altitudes, having a heart or lung disease, or having a bone marrow disease that causes the overproduction of red blood cells.

This article describes the various causes and symptoms of high and low hemoglobin levels and how each are treated.

For the purpose of this article, "male" refers to people born with penises and "females" refers to people with vaginas irrespective of the genders or genders they identify with or if they identify with any gender at all.

Causes of Low vs. High Levels of Hemoglobin

Verywell / Danie Drinkwater

High Hemoglobin Levels

A hemoglobin level above 17.5 for males and 15.5 for females is considered high. That can be due to a variety of causes.


Your cells need oxygen to survive. Your body may make excess hemoglobin at times when it's struggling to get enough oxygen to your cells. More hemoglobin leads to better oxygen delivery.

You can also have a high hemoglobin level if your body makes too many red blood cells. It may do that due to disease. Some diseases trigger the extra production themselves, while some cause low levels that your body may try to compensate for.

High hemoglobin levels can also be caused by:

Being in a high-altitude location can raise your hemoglobin level temporarily until you get back to a lower elevation or until your body adjusts to the atmospheric pressure at a high elevation.


You can test high for hemoglobin levels if you're dehydrated, but that's only because your blood contains less water. Once you're hydrated, the number should go back to normal.


Generally, a high hemoglobin level doesn't cause any symptoms. However, it can lead to some serious, potentially life-threatening complications. These include:


The treatment for high hemoglobin levels depends on what's causing it. If it's caused by a disease, treating that disease should help lower levels.

That may mean:

In some situations, you may need a blood transfusion to give your body enough red blood cells. This can be a one-time treatment in situations that cause a temporary increase in hemoglobin levels. For chronic conditions, you may need periodic transfusions.

Low Hemoglobin Level

A hemoglobin level below the normal value (13.5 for males, 12 for females) is considered low. Usually, a low hemoglobin level is a sign of iron deficiency anemia.

Causes and Risk Factors

You can develop a low hemoglobin level if you don’t make enough red blood cells or if you lose them faster than your body can replenish them.

Low hemoglobin levels are caused by: 

Excess Fluid

You can have low hemoglobin levels if your blood contains excess fluid (the opposite of dehydration.) That can be caused by some medical conditions, especially kidney failure.


A low hemoglobin level commonly causes noticeable symptoms. They include: 

  • Low energy 
  • Sleepiness
  • Pale skin 
  • Headaches 
  • Dizziness

Very low hemoglobin can cause:


Treatment for a low hemoglobin level depends on the cause. It may include: 

If you're being treated with chemotherapy or another medication that causes low hemoglobin levels, you'll probably need to stay on the medication, but also have treatments to increase hemoglobin production.

What Is Anemia?

Anemia is a low red blood cell count or diminished red blood cell function. Many things cause anemia, including low iron in the diet.


Your hemoglobin level reflects the number of red blood cells in your body and how efficiently they carry oxygen to your cells. This protein contains iron, which can be measured with a blood test.

Many things cause low or high hemoglobin, and they produce a variety of symptoms. Usually, the symptoms of low hemoglobin are more noticeable than symptoms of high hemoglobin and can lead to complications.

Most causes of hemoglobin abnormalities can be treated with medication. Sometimes a blood transfusion is necessary to correct very low hemoglobin levels. 

A Word From Verywell 

Hemoglobin is an important protein in your blood that can be measured with a simple blood test. Your hemoglobin level reflects the health of your red blood cells and how well your body can get oxygen.

If your hemoglobin level is too high or too low, you should not ignore it. Your medical team can find the cause and recommend treatments to reduce symptoms and prevent complications.

Frequently Asked Questions

  • What is a critical hemoglobin level?

    A hemoglobin level below 5.0 g/dL can lead to heart failure and death. Hemoglobin levels above 20 g/dL can lead to blood clots.

  • Can certain foods help regulate your hemoglobin count?

    If you have mild iron deficiency anemia, you can sometimes normalize your normal hemoglobin level by eating enough foods that contain iron:

    • Red meat
    • Shellfish
    • Beans
    • Spinach
    • Kale
    • Fortified grains
  • How can I prevent irregular hemoglobin levels?

    The best way is to not smoke cigarettes. Smoking itself raises levels, plus it increases your risk of chronic lung disease, heart disease, and cancer, which also raise hemoglobin levels.

    To prevent low hemoglobin levels, be sure to get enough iron in your diet.

4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Heidi Moawad, MD
Heidi Moawad is a neurologist and expert in the field of brain health and neurological disorders. Dr. Moawad regularly writes and edits health and career content for medical books and publications.