Low Hemoglobin, Explained

Hemoglobin carries oxygen throughout the body. When hemoglobin is low, your body isn’t getting the oxygen it needs. This can lead to a range of symptoms.

A healthcare worker draws blood from a person's arm

Yoshiyoshi Hirokawa / Getty Images

Hemoglobin is a protein in red blood cells that carries oxygen throughout your body. Sometimes, hemoglobin levels can get too low. There are many reasons why a person may experience low hemoglobin levels, ranging from specific medical conditions to nutritional deficiencies.

Low hemoglobin is something that should be dealt with, and thankfully there are effective ways of addressing it. The best treatment will depend on what’s causing the low levels.

What Is Hemoglobin?

Hemoglobin is a protein in red blood cells. Hemoglobin is made up of two parts: a protein (globin) and a compound called heme, which comprises iron atoms and a red pigment (porphyrin). This pigment is what gives blood its red color.

Hemoglobin’s job is to carry oxygen throughout the body and to carry carbon dioxide out of the body. That means the ability of your body to be properly oxygenated depends directly on the amount of hemoglobin in your body. 

What Is Considered Low Hemoglobin?

Levels of hemoglobin are measured through a hemoglobin test. This test is usually part of a complete blood count, which is a blood test that measures various aspects of your blood.

While the normal range might slightly differ from lab to lab, normal hemoglobin levels typically fall within the following ranges:

  Normal Hemoglobin Count in Grams per Deciliter (g/dL) Normal Hemoglobin Count in Grams per Liter (g/L) 
Men 13.8-17.2 138-172
Women 12.1-15.1 121-151
Newborns 14-24 140-240
 Infants 9.5-13 95-130

Anything below these levels can be considered low. It signals that your body is not getting the oxygen it needs. 

What Is a Critically Low Hemoglobin Level?

While the reason behind low hemoglobins should be diagnosed, receiving a lab test result that shows low hemoglobin levels is not usually a medical emergency. However, hemoglobin levels can get so low that the situation can be considered serious.

Critically low hemoglobin levels can lead to severe outcomes. For instance, a hemoglobin level less than 5.0g/dL may lead to heart failure or death. Hemoglobin less than 6.5g/dL may even be considered life-threatening.

What Causes Low Hemoglobin?

Low hemoglobin is often tied to anemia, a condition in which you have an abnormally low level of healthy red blood cells. Anemia most commonly develops from not getting enough iron, which is needed to make hemoglobin. This is known as iron-deficiency anemia.

Low hemoglobin is also associated with pernicious anemia, which is when your red blood cell levels drop because your intestines can’t absorb vitamin B12, as well as hemolytic anemia, which is when red blood cells are destroyed faster than they can be made. 

The following can also cause low hemoglobin:

  • Thalassemia, an inherited blood disorder that causes your body to have less hemoglobin than normal
  • Sickle cell disease and other genetic diseases that affect hemoglobins
  • Liver disease
  • Hypothyroidism
  • Bleeding, whether over time or suddenly
  • Systemic lupus erythematosus
  • Chronic kidney disease
  • Too much water in the body
  • Malnutrition
  • Sarcoidosis
  • A lack of folate or vitamin B12

Cancers can also contribute to low hemoglobin. These cancers include:

  • Leukemia
  • Lymphoma
  • Multiple myeloma
  • Any cancer that spreads to the bone marrow, where hemoglobin is made

Cancer treatment might also affect hemoglobin levels. A review of past studies showed that people with different types of cancers receiving chemotherapy experienced quick decreases in their hemoglobin—down to about 10g/dL. The decrease was especially prevalent for people who were 65 or older. 

Radiation therapy can also lower hemoglobin levels. For both chemotherapy and radiation cancer treatments, the lower levels can be due to the treatments’ effect on bone marrow, making it so that the bone marrow is unable to make new red blood cells. 

When bone marrow is unable to make red blood cells for any reason, including infection or a bone marrow disorder, low hemoglobin levels can develop. 

Symptoms of Low Hemoglobin

Some people with low hemoglobin, especially if it’s only a little below a normal range, may not experience any obvious symptoms. Others may have symptoms, especially as time goes on or the condition becomes more serious. 

Signs of low hemoglobin are related to reduced oxygenation of the blood, since hemoglobin is responsible for transporting oxygen throughout the body.

Common symptoms of low hemoglobin include:

  • Dizziness or fainting
  • Muscle weakness
  • Fatigue
  • Pale skin
  • Headache

How Is Low Hemoglobin Treated? 

The way that low hemoglobin is treated depends on the cause. If your blood test shows low hemoglobin, your healthcare provider will determine what is causing the low levels. Once you receive a diagnosis, you can be put on a proper treatment.

 Some of the possible treatments for low hemoglobin include:

  • Blood transfusion: Low hemoglobin caused by significant blood loss usually requires a blood transfusion, which is when you are given healthy blood through an IV line.
  • Vitamin supplementation: If your low hemoglobin is caused by dietary deficiencies, you will likely be given vitamin supplements containing iron, folic acid, and vitamin B12. Your hemoglobin levels will usually increase in six to eight weeks
  • Intravenous (IV) infusion: People who need to increase their iron levels quickly may require an IV infusion of iron or B12.
  • Bone marrow transplants: Low hemoglobin caused by cancers often require bone marrow transplants.

When a chronic condition is causing the low levels, treatment will involve managing that condition.

 Can You Prevent Low Hemoglobin?

Depending on the cause, it’s not always possible to prevent low hemoglobin. For example, blood loss from an injury or surgery isn’t within a person’s control. However, low hemoglobin from diet can be controlled. To make sure the food you eat helps fuel hemoglobin production, it is key to take in enough iron and B12. 

Meat is a top source for these nutrients. So if you are vegan or vegetarian, it may be particularly important to talk with a healthcare provider about making sure you are getting enough iron and B12 in your diet. There are several vegetarian and vegan sources of the nutrients, too, though. 

Foods that can help with hemoglobin levels include:

  • Red meat
  • Fatty fish
  • Turkey
  • Chicken
  • Tofu
  • Beans and lentils
  • Dark, leafy greens like kale, spinach, chard, or collard greens
  • Cereal, bread, and pasta that are fortified with iron and B12
  • Dried fruits

The best way to maximize your iron intake when eating plant-based food is to eat vitamin C-rich foods at the same time. Vitamin C-rich foods to pair with iron-rich foods are:

  • Citrus fruits
  • Berries
  • Tomatoes

Dietary supplements might be an option, too.  Ask a healthcare provider if that is the right option for you. They may recommend taking an iron, B12, or folic acid supplement.  

A Quick Review

Hemoglobin is a protein in your red blood cells that carries oxygen throughout your body. When you have low hemoglobin, your body is not getting as much oxygen as it should. This can lead to symptoms like dizziness, fatigue, a racing heart, trouble concentrating, and fainting. There are many causes of low hemoglobin. Anemia is a common cause. Cancer, cancer treatment, and certain chronic conditions can also cause low hemoglobin. Once a blood test shows that your levels are low, a healthcare provider will determine what’s causing it. Once the cause is diagnosed, there are several effective treatments for low hemoglobin that will allow you to feel well again.

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