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.

A low hemoglobin count is generally defined as less than 13.2 grams of hemoglobin per deciliter (132 grams per liter) of blood for men and less than 11.6 grams per deciliter (116 grams per liter) for women. In children, the definition varies with age and sex. These thresholds may differ slightly from one medical practice to another.

In many cases, a low hemoglobin count that's only slightly lower than normal doesn't affect how you feel. A low hemoglobin count that's more severe and causes symptoms might mean you have anemia.

Normally low hemoglobin counts

A slightly low hemoglobin count isn't always a sign of illness — it can be normal for some people. Women with menstrual periods and pregnant women 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 have 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 antiretroviral drugs for HIV infection and chemotherapy drugs for cancer and other conditions
• Chronic kidney disease
• Cirrhosis
• Hodgkin lymphoma (Hodgkin disease)
• Hypothyroidism (underactive thyroid)
• Inflammatory bowel disease (IBD)
• Iron deficiency anemia
• Lead poisoning
• Leukemia
• Multiple myeloma
• Myelodysplastic syndromes
• Non-Hodgkin's lymphoma
• Rheumatoid arthritis
• 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

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

• Bleeding in your digestive tract, such as from ulcers, cancers or hemorrhoids
• Frequent blood donation
• Heavy menstrual bleeding (heavy menstrual bleeding-although even normal menstrual bleeding may cause a slightly low hemoglobin count)

Some people learn that their hemoglobin is low when they try to donate blood. Being turned down for blood donation isn't necessarily a cause for concern. You can have a hemoglobin count that's fine for you but doesn't meet the standards blood donation centers set.

If your hemoglobin count is only a little under the required level, particularly if you've been accepted for blood donation in the past, you might just need to wait a couple of months and try again. If the problem continues, make an appointment with your doctor.

Make an appointment if you have signs and symptoms

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

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

Your doctor might recommend a complete blood count test to determine whether you have a low hemoglobin count. If your test reveals that you have a low hemoglobin count, you'll likely need more testing to determine the cause.