What is Hemoglobin?

Hemoglobin is a protein found inside red blood cells that helps transport oxygen throughout the body. It consists of two chains of amino acids - one containing iron (known as heme) and the other is globin. Hemoglobin is essential to life as it carries oxygen from our lungs to our cells and tissues.

Structure of Hemoglobin

The structure of hemoglobin is that of four globin chains connected to a central heme group containing four iron atoms, one of each attached to a nitrogen atom in the porphyrin ring. Heme carries one oxygen molecule per iron atom. When oxygen binds to the heme unit, a structural change caused by the binding of oxygen to the iron atom triggers two adjacent globin molecules to move closer together.

Preparation and Procedure

Testing for Hemoglobin levels is done by taking a sample of blood and measuring the level of Hemoglobin in it. The sample is usually taken from a vein in the arm. The health professional taking the sample will use a needle and syringe, or may use a special device that takes a very small amount of blood. The sample is then placed into a test tube and sent to a lab for analysis.

Types of Hemoglobin

  • Hemoglobin A (HbA) - This is the most common type and is found in adults.
  • Hemoglobin-A2 (HbA2) - This is a minor component of Hemoglobin in adults and is highest in newborns.
  • Hemoglobin F (HbF) - This type of Hemoglobin is found in fetuses and babies in the first six months after birth.


Low levels of Hemoglobin can cause fatigue and shortness of breath. Additional symptoms include pale skin, dizziness, rapid heartbeat, and headache. If left untreated, low Hemoglobin can also lead to anemia. High levels of Hemoglobin can also be a cause for concern as it is an indicator of dehydration or possible kidney or heart failure.

Why Test for Hemoglobin?

Testing for Hemoglobin levels can help to diagnose anemia, dehydration and other medical conditions. It is also important to monitor levels of Hemoglobin if a person has a medical condition that affects their red blood cells. In addition, it may be used to monitor the progress of blood transfusions and treatments for iron-deficiency anemia.

When to Test for Hemoglobin

A Hemoglobin test if often done at regular check-ups. It may also be ordered if a person is experiencing symptoms of anemia or if there are concerns that they may be at risk of developing anemia or chronic diseases. It is also often ordered prior to surgery or physical activities that may increase risk of anemia.