Packed Cell Volume Estimation - Methods, Normal Range, and Significance

What Is Packed Cell Volume Estimation?

Blood is a fluid of life and contains blood cells– red blood cells, white blood cells, and platelets which are present in the liquid portion of blood called plasma.

Packed cell volume is the proportion of blood occupied by red blood cells and is calculated in percentage. When the blood sample is taken in the hematocrit tube and centrifuged, the components of the blood get separated into three marked layers; in the bottom, a layer of red blood cells is present, then a layer of white blood cells and platelets and a layer of plasma on the top. Red blood cells' content varies from low to high and can lead to certain blood disorders.

What Are Red Blood Cells?

• Red blood cells are non-nucleated cells present in the blood.

• The red color of the red blood cells is due to the presence of the pigment called hemoglobin.

• Red blood cells play an essential role in the transportation of respiratory gasses, i.e., oxygen and carbon dioxide.

• Normally, the shape of the red blood cells is disk-like and biconcave (dumbbell shape), and the count ranges between 4 to 5.5 million/cu mm of blood. The average lifespan of red blood cells is 120 days.

What Is the Function of Red Blood Cells?

Following are the significant functions of red blood cells-

1. Transport of oxygen from the lungs to the tissues.

2. Transport of carbon dioxide from the tissues to the lungs.

3. Buffering action in blood.

4. In the blood group determination.

What Is the Method of Determination of Packed Cell Volume?

There are two methods of determining the packed cell volume.

• Macrohematocrit Method - To determine the packed cell volume, there is a requirement of the specimen, hematocrit or Wintrobe tube, centrifuge machine, and Pasteur Pipette.

• Collection of the Specimen in Macrohematocrit Method - Samples can be collected from random venous blood while maintaining proper precautions. Blood can be collected in the anticoagulant ethylenediaminetetraacetic acid (EDTA). For the determination of packed cell volume, blood mixed with the anticoagulant is necessary.

• Testing Procedure of the Blood Sample In Macrohematocrit Method -The blood sample is collected in the Wintrobe tube up to mark 100 mm (millimeters) with the help of the pipette, then placed in the centrifuge machine. The centrifuge machine is set to spin at 3000 rpm (rotation per minute) for 30 minutes.

After the centrifugation, the test tube is taken out, and the blood gets divided into three layers. The bottom layer of red blood cells is also called —hematocrit (HCT), then a buffy coat; this layer contains white blood cells, platelets, and plasma at the top.

• Microhematocrit Method - The Microhematocrit method refers to the procedure in which a less amount of blood can be used as a sample for testing.

• Collection of Specimens Microhematocrit Method - For the Microhematocrit method, samples collected of the blood can be less than a single finger prick is also efficient. The blood is taken in a test tube filled with heparin.

• Testing Procedure of the Blood Sample Microhematocrit Method - The blood collected in the capillary filled with heparin is placed in the centrifuge machine for centrifugation at the speed of 11,000 - 12,000 rpm for 4 to 5 minutes. By this method, the size and number of red blood cells can be measured by the resistance exerted by the blood through the two electrodes.

What Is the Significance of Determining Packed Cell Volume?

Determination of the packed cell volume helps in -

1. Diagnosis and treatment of anemia.

2. Diagnosis and treatment of polycythemia.

3. Determination of extent of dehydration and recovery from the dehydration after treatment.

4. The decision of blood transfusion.

5. Treatment of cancer.

6. Chronic medical problems.

What Are the Normal Ranges of the Packed Cell Volume?

Normal range of packed cell volume -

• In newborn- 45% - 61%

• In infant - 32% - 42%

• In males - 40% - 45%

• In females - 38% - 42%

What Happens if the Packed Cell Volume Is High?

If the packed cell volume is higher than the normal range, it means the body is making too many red blood cells. Related diseases involve increased packed cell volume -

• Polycythemia - Polycythemia is the abnormal increase in the red blood cell count. Red blood cell count increases above 7 million/cu mm of blood. It is of two types primary and secondary.

• Dehydration - Dehydration refers to the loss of water from the body.

• Dengue Shock Syndrome - Dengue fever (a tropical disease caused by the flavivirus transmitted by a mosquito) of grade III or IV severity.

• Lung Disease - Insufficient oxygen supply leads to improper absorption of oxygen, because of which the body tends to increase the production of red blood cells.

• Heart Disease - Increased packed cell volume affects the cardiac output.

What Happens if the Packed Cell Volume Is Low?

If the packed cell volume is lower than the normal range, it means the body does not have enough red blood cells, or the blood cells are abnormal in shape and size and get destroyed early.

Related diseases involving decreased packed cell volume.

• Anemia is a blood disorder characterized by the reduction of red blood cells and hemoglobin content.

• Cirrhosis of the liver refers to the inflammation and damage of the parenchyma of the liver.

• In pregnancy, due to low packed cell volume, there is a chance of premature birth of the baby associated with a low birth weight of the baby and postpartum depression.

• Hemorrhage due to ectopic pregnancy (pregnancy due to implantation of the fertilized ovum in tissues other than the uterine wall), which is characterized by vaginal bleeding.

• Low packed cell volume can induce bone marrow disorders such as aplastic anemia, myelodysplastic syndrome, leukemia, lymphoma, or myeloma.

What Are the Other Factors Affecting the Abnormal Range of Packed Cell Volume?

• There are several conditions in which the packed cell volume is deviated from normal, but that does not mean any medical emergency.

• In newborn babies, the packed cell volume is elevated, which gradually decreases as the neonatal phases are completed.

• In pregnancy, the packed cell volume is low, which is normal because of hemodilution (decreased hemoglobin content in the blood).

• People living in higher altitudes have high packed cell volumes because of less oxygen. Packed cell volume may vary in different ages, sex, location, and other medical conditions.

How to Calculate the Packed Cell Volume?

Blood indices are the calculation derived from the red blood cell count, hemoglobin count of the blood, and packed cell volume.

Blood Indices Include -

1. Mean Corpuscular Volume (MCV) - Mean corpuscular volume is the average volume of a single red blood cell, and it is expressed in cubic microns (cu). The normal mean corpuscular volume is 90 cu (78 to 90 cu ).

2. Mean Corpuscular Hemoglobin Concentration (MCHC) - Mean corpuscular hemoglobin concentration is the concentration of hemoglobin in one red blood cell. It is the amount of hemoglobin expressed in the volume of one red blood cell. So the unit of expression is the percentage. The normal value of mean corpuscular hemoglobin concentration is 30% (30% to 38%).

Conclusion

Packed Cell volume is done to diagnose any disorder. It is involved in routine health check-ups under complete blood count (CBC). The methods of determination of packed cell volume are easy to perform and cost-effective. If the packed cell volume shows some abnormal values, one should seek medical attention.