Blood is a specialized body fluid that comprises blood platelets, white blood cells, red blood cells, and blood plasma. Red blood cells, which are also referred to as erythrocytes, perform the vital function of transporting oxygen. Hematocrit, which is also called packed cell volume, refers to the percentage of blood volume that is made up of the red blood cells. The red blood cells contain a conjugated iron-carrying protein called hemoglobin. Hemoglobin not only imparts red color to the red blood cells, it also transports oxygen-rich blood to the cells and tissues of the body. Oxygen from the lungs binds to the iron within the hemoglobin molecules to form a compound called oxyhemoglobin. Besides transporting oxygen to the bodily tissues, hemoglobin molecules also bind to carbon dioxide, and transport carbon dioxide from the tissues to the lungs.

Since hemoglobin is associated with the oxygen-carrying capacity of blood, problems could arise if hemoglobin levels are lower or higher than the normal range. High levels of hematocrit could also be indicative of health problems.

Causes of Elevated Hematocrit and Hemoglobin

When the hematocrit value is higher than the normal range, it is usually indicative of an elevated red blood cell count. Hematocrit values could be affected by the size, as well as the numbers of the red blood cells. High hemoglobin and hematocrit could be a sign of polycythemia vera. Here are some of the common contributing factors for high levels of hemoglobin, as well as hematocrit.

Polycythemia vera
This is a medical condition wherein the body produces too many red blood cells. This leads to increased blood volume and viscosity. Affected individuals are at a great risk of developing complications due to clotting or bleeding problems. Phlebotomy is often suggested for people affected by this condition. During this procedure, an incision is made in a vein for collecting venous blood. This helps in reducing the blood volume.

Dehydration could also alter the hemoglobin and hematocrit values, as loss of fluids reduces the blood volume. As a result, the number of red blood cells would be higher in comparison to the blood volume.

Conditions that Cause Hypoxia
Heart and lung conditions that are characterized by low oxygen levels can also affect the hematological values. Heart failure, enlargement of the right ventricle of the heart due to pulmonary diseases (cor pulmonale), emphysema, pulmonary fibrosis, chronic obstructive pulmonary disease, etc., are some conditions that may cause high hemoglobin levels. When the blood oxygen levels are low, the body produces more red blood cells to compensate for low oxygen levels. The kidneys increase the production of erythropoietin, which is a glycoprotein that stimulates red blood cell production in the bone marrow. This is the reason why smokers and the people who live at higher altitudes may have higher hematocrit levels.

Blood Doping
The term 'blood doping' refers to illegal methods of improving athletic performance. It involves increasing the amount of hemoglobin in the blood by blood transfusions, or the use of injections of synthetic oxygen carriers or erythropoietin. Erythropoietin stimulating agents cause the bone marrow to produce more red blood cells. The use of anabolic androgenic steroids also increase the production of red blood cells, which in turn elevates the hemoglobin levels.

Normal Range for Hematocrit and Hemoglobin

The normal reference range of hematocrit for men is 40.7 to 50.3%, whereas reference range for women is 36.1 to 44.3%. The normal range for red blood cell count for men is 4.7 to 6.1 million cells per microliter. In case of women, the normal range is 4.2 to 5.4 million cells per microliter. The reference range for hemoglobin, hematocrit, and the RBC indices may slightly differ from one laboratory to another.

Normal Range for Hemoglobin
AgeHemoglobin (g/dL)
Less than 1 month10.0-20.0
1-2 months10.0-18.0
2-6 months9.5-14.0
6 months-2 years10.5-13.5
2-6 years11.5-13.5
6-12 years11.5-15.5
12-18 years (females)12.0-16.0
18 years and above (females)12.1-15.1
12-18 years (males)13.0-16.0
18 years and above (males)13.8-17.2

It must be noted that elevated levels of hemoglobin or hematocrit could be indicative of certain medical conditions. So, if the CBC test reveals abnormal values for hemoglobin and hematocrit, other diagnostic tests must be conducted to identify the underlying cause.

Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.