What is the hemoglobin test?
A hemoglobin test measures the amount of hemoglobin in your blood. Hemoglobin is a protein that is the main component of red blood cells (erythrocytes). Red blood cells are produced in the bone marrow. Hemoglobin contains iron, which allows it to bind to oxygen. Red blood cells transport oxygen from the lungs to other tissues and organs. They also carry carbon dioxide to the lungs so it can be removed from the body.
Lower than normal hemoglobin levels, otherwise known as anemia, can indicate that the organs of your body might not be getting an adequate supply of oxygen. This can lead to a lack of energy, fatigue, or other problems.
Low levels of hemoglobin may be a sign that the bone marrow is not producing enough red blood cells, or that cells are being destroyed faster than they are made. Chronic blood loss also leads to a drop in hemoglobin levels and is one of the most common causes of anemia.
Why is a hemoglobin test done?
A hemoglobin test may be performed along with a routine physical examination to assess the amount of hemoglobin in your blood. It is done as part of a complete blood count (CBC) test, which looks for the numbers of red blood cells, white blood cells, and platelets in a blood sample. A CBC is also done when there are symptoms of a low hemoglobin level, such as fatigue, weakness, or dizziness.
There are many disorders that result in low hemoglobin levels or anemia, including:
- Iron deficiency, which is almost always caused by blood loss
- Deficiency of other nutrients, such as vitamin B12 or folic acid
- Internal or external blood loss resulting from surgery, injury, menstrual bleeding, or bleeding from the gastrointestinal tract
- Thalassemia, a common inherited blood disorder caused by genetic mutations in the hemoglobin genes. It is usually mild but severe forms can cause symptoms in childhood.
- Kidney disease
- Autoimmune diseases
Symptoms indicating low red blood cell levels may include:
- Pale skin (pallor)
- Shortness of breath
- Cold hands and feet
The hemoglobin test may be used to screen for anemia and other blood disorders and monitor the progress during treatment. It can only establish whether anemia is present and its degree of severity. The test cannot detect what is causing the abnormal level of hemoglobin. Additional tests are required.
Some conditions result an increase in red blood cells in the body, causing an excess of hemoglobin in the blood. These disorders include:
- Polycythemia vera: A rare blood disease where the bone marrow produces too many red blood cells. It is usually caused by a genetic mutation, although the disease is not inherited.
- Congenital heart defects
- Certain types of kidney diseases, including kidney cancer
- Lung disease, including chronic pulmonary obstructive disease (COPD) and pulmonary fibrosis
Too many red blood cells can cause the blood to thicken and become sluggish. Thick blood does not flow as quickly, which can deprive the organs of oxygen.
Symptoms of excess levels of red blood cells may include
- Blurred or double vision
- Blood clots
What preparation is needed before the hemoglobin test is performed?
A hemoglobin test does not require any special preparation. It usually takes only a few minutes. The test can be done in a doctor’s office, medical laboratory or other outpatient setting.
How is the hemoglobin test done?
A blood sample will be required. A small needle will be inserted into a vein, usually in your arm or hand. Blood may be drawn from another part of the body, if necessary. For children, a finger stick might be used to obtain blood. A heel stick may be done for newborns.
The medical professional will swab the skin near the area with alcohol before drawing blood. He or she will place an elastic band around your upper arm and ask you to make a fist to make blood flow easier. You may experience some mild pain or discomfort as the needle is inserted. Your blood will be collected in a small vial or vials and sent to the lab to be analyzed.
The area around the puncture may appear bruised or swollen for a few days.
The risks associated with the hemoglobin test are very small. In most cases, there are no significant aftereffects.
Results and Follow-Up
What do the test results indicate?
The normal range for hemoglobin levels is 12 to 17.4 grams per deciliter of blood for adults. However, levels may vary depending on a person’s age and race. Altitude can also affect the results.
What follow-up is required?
Your doctor will discuss the results of the hemoglobin test with you. The doctor may order more tests, depending on its outcome. Treatment will depend on the underlying condition. You should discuss treatment options with your doctor. You may have to have hemoglobin tests on a regular basis, if you are undergoing treatment for a blood disorder.