The key difference between hemoglobin and hematocrit is that hemoglobin is a protein present mainly in the red blood cells of almost all vertebrates while hematocrit is a measurement related to total blood count.
Both hemoglobin and hematocrit are used to diagnose anemia, which is a disease condition that develops when the blood produces a lower-than-normal amount of healthy red blood cells. Therefore, these two terms are mistaken to be the same thing frequently.
CONTENTS
1. Overview and Key Difference
2. What is Hemoglobin
3. What is Hematocrit
4. Hemoglobin vs Hematocrit in Tabular Form
5. Summary – Hemoglobin vs Hematocrit
What is Hemoglobin?
Hemoglobin is a metallo-protein containing a heme group and globin proteins. The heme group contains iron and has the ability to get bound to oxygen with great affinity. Hemoglobin is symbolized by Hb. It is present in vertebrates and some invertebrates. The function of hemoglobin is mainly transporting oxygen from the lungs (or gills) to other tissues as oxyhemoglobin, to be used in cellular respiration. From tissues, carbon dioxide is transported back to the lungs as carboxyhemoglobin.
Hemoglobin also has the ability to transport nitric oxide molecules; a crucial player in cell signaling processes. Hemoglobin is responsible for the red color of red blood cells. It is also present in some neurons, macrophages, alveolar cells, etc., but the functions are different from hemoglobin present in red blood cells. One such function is working as an antioxidant in iron metabolism. In mammals, hemoglobin makes up to 97% of the dry weight of red blood cells and up to 35% of the wet weight. The presence of hemoglobin in blood has increased blood’s ability to transport oxygen by seventyfold when compared to oxygen merely being dissolved in the blood. When red blood cell count drops it is an indication of a low level of red blood cells or heme production which results in anemia, and the frequent symptoms are fatigue, lack of concentration, and exercise intolerance. Having very low hemoglobin counts can be lethal due to low oxygen supply to tissues.
What is Hematocrit?
Hematocrit abbreviated as HCT or Ht is also known as erythrocyte volume fraction (EVF) or packed cell volume (PCV). What it measures is the percentage volume of red blood cells in the blood. The count is generally 45% for men and 40% for women. Hemoglobin count is actually a part of hematocrit. It is observed that hematocrit is independent of the body size in mammals.
There are many ways of determining hematocrit. The classical method is centrifuging heparinized blood and separating blood into different layers and calculating volume percentage using layer heights. The modern method is using an automated analyzer. In a patient who is under red blood cell supplements hematocrit may be artificially high. In a patient who is under saline supply hematocrit is low due to the dilution of blood. High hematocrit is a sign of dengue shock syndrome. Hematocrit and hemoglobin level changes parallel to each other. Therefore, one of the two is enough to determine anemia.
What is the Difference Between Hemoglobin and Hematocrit?
The key difference between hemoglobin and hematocrit is that hemoglobin is a protein present mainly in the red blood cells of almost all vertebrates while hematocrit is a measurement related to total blood count. In other words, hemoglobin is a protein but hematocrit is not a protein; it is a measurement. Hemoglobin is a part of hematocrit because hematocrit is a measure of total red blood cells where hemoglobin is only a component. Moreover, hemoglobin count and hematocrit change parallelly. (If one is low, the other too is low, and vice versa.)
Summary – Hemoglobin vs Hematocrit
Both hemoglobin and hematocrit are used to diagnose anemia. Hemoglobin is a protein but hematocrit is not a protein; it is a measurement. This is the key difference between hemoglobin and hematocrit.
Image Courtesy:
1. “1GZX Haemoglobin” By Zephyris at the English-language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Packed cell volume diagram” By MesserWoland – own work created in Inkscape, based on w:en:user:Tristanb's graphics. (CC BY-SA 3.0) via Commons Wikimedia