Hemoglobin Test

A hemoglobin test evaluates the amount of hemoglobin in the blood. Hemoglobin is an iron-containing protein found in red blood cells that is responsible for carrying oxygen to different body organs and tissues. They also transport carbon dioxide from the organs and tissues back to the lungs.


A hemoglobin test can be performed alone or with a hematocrit. It is a test that measures the amount of blood that is made up of RBCs to evaluate red blood cells. It is also one of the parameter of complete blood count (CBC). CBC is a group of tests that is often used in the general assessment of health.


Red blood cells make up about 40% of the total blood's volume and are produced in the bone marrow. When they become mature, they are released into the bloodstream. The lifespan of an RBC is approximately 120 days, and the bone marrow continually produces new RBCs to replace those that degrade or are lost through bleeding.


Several diseases and conditions can affect the level of RBCs in the blood. In general, the hemoglobin and hematocrit rise than normal when the number of red blood cells increases. Similarly, hemoglobin levels and hematocrit fall to a lesser number when there is a decrease in RBCs.


There are some conditions that affect RBC production in the bone marrow and may cause fluctuation in the counting of mature RBCs released into the bloodstream. If there is higher destruction of RBCs (hemolysis) or loss of RBCs through bleeding or the bone marrow is not able to manufacture new RBCs fast enough, the total number of RBCs and hemoglobin will drop, increasing the risk factor of anaemia.


Anemia is a medical condition in which tissues and organs do not get enough oxygen, causing fatigue and weakness. More than sufficient RBCs production results in polycythemia, and the blood can become thickened.


Purpose of hemoglobin test


A doctor can recommend a hemoglobin test for several reasons:


To evaluate overall health: A healthcare provider may test hemoglobin as part of a complete blood count during a routine medical checkup to monitor general health and to screen for various disorders, such as anemia.


To diagnose a medical condition: A doctor may suggest a hemoglobin test if a person is experiencing weakness, dizziness, fatigue, or shortness of breath. These signs and symptoms can be an indication of anemia or polycythemia vera. A hemoglobin test may help diagnose these conditions.


To monitor a medical condition: If an individual has been diagnosed with anemia or polycythemia vera, the doctor may use a hemoglobin test to observe their condition and guide treatment.


Why does anyone need a hemoglobin test?


A health care provider may order the test as part of a routine exam, or if a person has:

  • Symptoms of anemia - weakness, dizziness, pale skin, cold hands, and feet, etc.
  • A family history of an inherited blood disorder such as thalassemia, sickle cell anemia, and many others
  • A diet low in iron and minerals
  • A long-term infection
  • Excessive blood loss


What happens during a hemoglobin test?


A health care professional or a technician will take a blood sample from a vein in the arm using a small needle. After the needle is inserted, a small volume of blood will be withdrawn into a test tube or vial. A person may feel a little sting when the needle goes in or out. The process hardly takes less than five minutes.


Any preparation required?


Generally, a patient needs no special preparations for a hemoglobin test. If the patient has been ordered other blood tests along with a hemoglobin test, fasting may be required as per the test. A doctor will guide if there are any special instructions to follow.

Are there any risks to the test?


There is very little or no risk of having a blood test. A person may have slight pain or bruising at the spot where the needle was inserted, but most symptoms usually go away quickly.

Lower level of hemoglobin


Low level of hemoglobin can be a sign of:


  • Iron deficiency
  • Vitamin B-12 deficiency
  • Folate deficiency
  • Bleeding
  • Cancer such as leukemia
  • Liver disorder
  • Kidney disease
  • Hypothyroidism
  • Thalassemia - A genetic disorder in which the body makes an inadequate amount of RBCs and haemoglobin


Higher level of hemoglobin

Higher than normal hemoglobin levels may be a sign of:

  • Polycythemia vera - a blood disorder in which bone marrow makes more than sufficient RBCs
  • Lung disease
  • Dehydration
  • Living at a high altitude
  • Burns
  • Excessive vomiting
  • Extreme physical exercise
  • Heavy smoking


[These are suggestions based on studies. Please always consult a doctor for further information]


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