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Low hemoglobin count

Medically reviewed on April 7, 2018

Definition

A low hemoglobin count is a commonly seen blood test result. Hemoglobin (Hb or Hgb) is a protein in red blood cells that carries oxygen throughout the body.

In many cases, a low hemoglobin count is only slightly lower than normal and doesn't affect how you feel. If it gets more severe and causes symptoms, your low hemoglobin count may indicate you have anemia.

A low hemoglobin count is generally defined as less than 13.5 grams of hemoglobin per deciliter (135 grams per liter) of blood for men and less than 12 grams per deciliter (120 grams per liter) for women. In children, the definition varies with age and sex. The threshold differs slightly from one medical practice to another.

Causes

Normally low hemoglobin counts

A slightly low hemoglobin count isn't always a sign of illness — it may be normal for some people. Women who are pregnant commonly have low hemoglobin counts.

Low hemoglobin counts associated with diseases and conditions

A low hemoglobin count can be associated with a disease or condition that causes your body to have too few red blood cells. This can occur if:

  • Your body produces fewer red blood cells than usual
  • Your body destroys red blood cells faster than they can be produced
  • You experience blood loss

Diseases and conditions that cause your body to produce fewer red blood cells than normal include:

  • Aplastic anemia
  • Cancer
  • Certain medications, such as anti-retroviral drugs for HIV infection and chemotherapy drugs for cancer and other conditions
  • Chronic kidney disease
  • Cirrhosis (scarring of the liver)
  • Hodgkin's lymphoma (Hodgkin's disease)
  • Hypothyroidism (underactive thyroid)
  • Iron deficiency anemia
  • Lead poisoning
  • Leukemia
  • Multiple myeloma
  • Myelodysplastic syndromes
  • Non-Hodgkin's lymphoma
  • Vitamin deficiency anemia

Diseases and conditions that cause your body to destroy red blood cells faster than they can be made include:

  • Enlarged spleen (splenomegaly)
  • Hemolysis
  • Porphyria
  • Sickle cell anemia
  • Thalassemia
  • Vasculitis (blood vessel inflammation)

A low hemoglobin count can also be due to blood loss, which can occur because of:

  • Bleeding from a wound
  • Bleeding in your digestive tract, such as from ulcers, cancers or hemorrhoids
  • Bleeding in your urinary tract
  • Frequent blood donation
  • Menorrhagia (heavy menstrual bleeding)

When to see a doctor

Hemoglobin tests are given for many reasons, such as to screen for or help diagnose disease and to monitor treatment response. Some people learn that their hemoglobin is low when they go to donate blood. If you're told that you can't donate blood because of low hemoglobin, make an appointment with your doctor.

Make an appointment if you have signs and symptoms

If you experience signs and symptoms of a low hemoglobin count, make an appointment with your doctor. Signs and symptoms may include:

  • Fatigue
  • Weakness
  • Pale skin and gums
  • Shortness of breath
  • A fast or irregular heartbeat

Your doctor may recommend a complete blood count test to determine whether you have a low hemoglobin count or whether your signs and symptoms are caused by something else.

If your test reveals you have a low hemoglobin count, you will likely need more testing to determine the cause. Then your doctor can explain what this means for you.

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