What Causes High or Low Hemoglobin Levels?

Maintaining normal hemoglobin levels is important, as this blood protein carries oxygen to your cells. There can be slight variations between what different healthcare providers consider “healthy,” but in general, a healthy hemoglobin level for males aged 19–65 years is between 13.1 and 17.5 grams per deciliter of blood (g/dL). In adult females aged 19–65 years, a hemoglobin count of between 10.6 and 15.6 g/dL is typically considered normal and healthy. See table for more detail.

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 to fatigue, weakness, and other signs of anemia.

By contrast, a higher-than-normal hemoglobin count means that your body is being deprived of oxygen. This can be due to conditions like smoking, living at a high altitude, 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 is treated.

How Are Hemoglobin Levels Tested?

A hemoglobin test measures the amount of hemoglobin in your blood. The test requires a simple blood draw.

Your hemoglobin is typically tested as a part of a complete blood count (CBC). You don’t usually need to do anything to prepare for this test unless your healthcare provider has also ordered other tests to be done on the same blood sample. Make sure to ask your provider if you should fast before you arrive for the test.

A blood draw is done through a needle inserted into a vein in your arm. You will feel a small prick or sting and you may have bruising and soreness afterwards.

Factors That Affect Results

Several factors can affect your hemoglobin test results, including:

• Your age and sex
• Your posture while blood is being drawn
• Environmental conditions, such as temperature, humidity, and air pollution
• Intense exercise within 24 hours before testing

If your healthcare provider orders a blood test for you, ask them if there is anything you should or should not do leading up to your test. For the most accurate results, follow their directions carefully.

High Hemoglobin Levels

A hemoglobin level above the normal value is considered high. That can be due to a variety of causes.

Causes and Risk Factors

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:

• Polycythemia vera (a condition that increases levels of all blood cells)
• Heart, kidney, or lung disease
• Chronically low oxygen levels
• Dehydration
• Smoking tobacco
• Liver or kidney cancer
  

Your hemoglobin levels can also increase temporarily while you are in a high-altitude location. This will resolve on its own when you get back to a lower elevation or when your body adjusts to the atmospheric pressure at a high elevation.

Symptoms

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

• Blood clots
• Heart attack
• Stroke

Treatment

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:

• Medications for polycythemia vera 
• Medications or surgery for heart disease
• Oxygen supplementation, medications, or surgery for lung disease
• Cancer treatment
• Smoking cessation
  
• Fluids and electrolytes for dehydration 

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 Levels

A hemoglobin level below the normal value 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:

• Low dietary iron or impaired iron absorption 
• Menstrual bleeding
• Cancer, especially leukemia (blood-cell cancers) 
• Chemotherapy
• Blood loss from any cause, including surgery, trauma, or a gastrointestinal (stomach) bleed from an ulcer
  

Symptoms

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

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

Very low hemoglobin can cause:

• Tachycardia (rapid heart rate)
• Hypotension (low blood pressure)
• Dyspnea (trouble breathing)
  

Treatment

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

• Increasing iron in your diet through foods and/or supplements 
• Treating a bleeding ulcer to prevent recurrent blood loss 
• Cancer treatment
• Supplemental erythropoietin (EPO, a hormone in the kidneys that helps produce red blood cells)
• Treatments that stimulate bone marrow to raise red blood cell production 

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.

Summary 

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.