What Causes a Low or High Hemoglobin Level?

Many different conditions can cause hemoglobin abnormalities

Hemoglobin is an iron-containing protein that facilitates oxygen delivery to cells in the body. Your hemoglobin level can be measured with a complete blood count (CBC). According to the American Red Cross, a normal hemoglobin level is 13.5–17.5 grams per deciliter (g/dL) for males and 12–15.5 g/dL for females. The standard values can vary between different laboratories.

A CBC blood test is often part of a routine checkup, and it is also commonly ordered as part of the evaluation of medical symptoms, such as fatigue and fever.

High hemoglobin levels and low hemoglobin levels are indications of different medical problems. Usually, these conditions can be corrected with medication or other interventions. This article will discuss when low or high hemoglobin may occur, including symptoms, risk factors, and treatment.

Causes of Low vs. High Levels of Hemoglobin

Verywell / Danie Drinkwater

High Hemoglobin Level

A hemoglobin level above the normal value is considered high. There is a variety of causes.


Your body can make excess hemoglobin in circumstances that lower your ability to get adequate oxygen to your cells. Oxygen is needed for energy and cell survival. The excess hemoglobin can help you increase oxygen delivery to your cells.

You can also have a high hemoglobin level if your body makes too many red blood cells, which may happen to make up for low levels, or it can occur due to disease. The excess red blood cells often contain normal amounts of hemoglobin, which raises your overall hemoglobin count.

Low Hemoglobin Level

A hemoglobin level below the normal value is considered low. Usually, a low hemoglobin level is an indication of anemia.


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

You can also have a low hemoglobin measurement if your blood contains excess fluid, which can occur with some medical conditions, especially kidney failure.

What Is Anemia?

Anemia is a low red blood cell count or diminished red blood cell function. There are many different causes of anemia.


Often, high or low hemoglobin levels develop over time due to chronic disease, leading to effects that can worsen over the course of weeks or months. Acute conditions can rapidly lead to low hemoglobin, which may cause symptoms to develop quickly over days or hours. 

Generally, a high hemoglobin level does not cause symptoms, but it can lead to complications, including blood clots, heart attack, and stroke. 

A low hemoglobin count commonly causes noticeable nonspecific symptoms. Symptoms of low levels include: 

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

Very low hemoglobin can cause tachycardia (rapid heart rate), hypotension (low blood pressure), and dyspnea (trouble breathing). 

Risk Factors 

Many conditions can increase the risk of having low or high hemoglobin levels. 

High hemoglobin is caused by:

  • Polycythemia vera (a condition in which there are high levels of all blood cells)
  • Heart or lung disease 
  • Liver or kidney cancer 
  • Chronically low levels of oxygen 
  • Smoking 

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 high elevation.

You can have a high hemoglobin level on a blood test if you are dehydrated. This does not reflect a high level of hemoglobin in your body, and the measurement would be normalized once you are adequately hydrated. 

Low hemoglobin is caused by: 

You can develop a low hemoglobin level if your body isn’t making enough red blood cells or enough hemoglobin. Low hemoglobin levels also can result if your red blood cells are lost due to bleeding or become damaged due to disease. 


There are many treatments for low or high hemoglobin levels, and the treatment is determined based on the underlying cause.

In some situations, a blood transfusion may be necessary to provide the body with enough red blood cells. This can be a onetime treatment in situations where the production of red blood cells eventually catches up, or it may be necessary to have repeated blood transfusions to treat chronic diseases that cause low levels of hemoglobin.

Treatments for high hemoglobin include: 

Treatments for low hemoglobin include: 

  • Iron-containing foods in the diet or iron supplements for iron deficiency anemia 
  • Treatment of a bleeding gastrointestinal ulcer to prevent recurrent blood loss 
  • Treatment of cancer
  • Erythropoietin (EPO, a hormone in the kidneys that helps produce red blood cells) or other treatments that stimulate bone marrow to raise red blood cell production 

If you are being treated with chemotherapy or another medication that is causing low hemoglobin levels, you may need to continue to take the causative medication and also get treatment for your low levels. 


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, and it can be measured with a blood test.

There are many causes of 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 progress rapidly.

Most of the 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 will assess your hemoglobin level along with other tests to determine the cause. The underlying cause can usually be effectively treated to reduce symptoms and prevent complications.

Frequently Asked Questions

  • What is the normal hemoglobin level?

    A normal hemoglobin level is 13.5–17.5 grams per deciliter (g/dL) for males and 12–15.5 g/dL for females.

  • Can certain foods help regulate your hemoglobin count?

    If you have mild iron deficiency anemia, you can sometimes attain a normal hemoglobin level by eating enough foods that contain iron. These include red meat, shellfish, beans, spinach, kale, and grains fortified with iron.

  • What is a critical hemoglobin level?

    A hemoglobin lower than 5.0 g/dL can lead to heart failure and death. Hemoglobin higher than 20 g/dL can lead to blood clots.

  • How can I prevent irregular hemoglobin levels?

    One of the best ways to lower your risk of abnormal hemoglobin levels is to avoid smoking, which can cause your hemoglobin level to be too high. Smoking can also increase the risk of chronic lung disease, which also raises hemoglobin.

    Smoking increases the risk of many types of cancer—sometimes cancer can cause high hemoglobin levels and sometimes it can cause low hemoglobin levels.

    Additionally, practicing a healthy lifestyle by staying active and maintaining a healthy weight can help you avoid heart disease, which is another cause of abnormal hemoglobin levels. 

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5 Sources
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