Blood Calculator

Formula

The blood calculator estimates the volume of blood expected to be in both the systemic and respiratory circulation.

There are two tabs available that cater to the Metric and English measurement units. The three patient variables required are gender, weight and height.

The Nadler method, used for estimating total blood volume, is gender specific. Two equations are available:

For men = 0.3669 x Height in m³ + 0.03219 x Weight in kgs + 0.6041

For women = 0.3561 x Height in m³ + 0.03308 x Weight in kgs + 0.1833

The above formulas are to be used in adult patients and children who weigh over 35 kg. For small children, the blood volume is estimated by adding 70 mL per kilogram.

In adults, the blood normally makes up 7-8% of human body weight. This is approximately 4.5 to 6 quarts (5 to 6 L) of blood.

One unit of blood (for example, for transfusion purposes) is equivalent to a pint.

Men, on average, have more blood than women, 4.5- 6 quarts of blood compared to 3.5- 4 quarts.

Blood components

Blood contains red cells, white cells, platelets and plasma, in similar proportions in healthy individuals.

Red blood cells, or erythrocytes, are specialized in the transport of oxygen from the lungs to all the tissues of the body and in the transport of carbon dioxide from the cells to the lungs to be exhaled.

White blood cells, or leukocytes, are responsible with the immune system. These can also be found in other organs of the body such as the spleen, liver and lymph glands.

Platelets, or thrombocytes, are specialized in the blood coagulation process and trigger clotting, thus preventing the body from losing too much blood in case of an injury. They interact with other proteins involved in blood clotting in a cascading manner.

Plasma is the liquid portion of the blood and makes up 55% of it. It is a fluid that contains water, proteins (e.g. albumin, gamma globulins, fibrinogen), hormones, sugars, fats, amongst other blood components.

About blood types

Blood types represent the classification of blood as reflected from the presence or absence of antigens and antibodies.

The blood group is determined by inherited genes. One of the most important blood group system is the ABO System. This is based on the presence or absence of the two antigens: A and B on the surface of the red cells:

■ Group A - has A antigens on the red blood cells and B antibodies in the plasma;

■ Group B - has B antigens on the red blood cells and A antibodies in the plasma;

■ Group AB - has both A and B antigens on the red blood cells and no antibodies;

■ Group 0 - has no antigens but has both A and B antibodies in the plasma.

References

1. Maton A, Hopkins J, McLaughlin CW, Johnson S, Quon Warner M, LaHart D, Wright JD. (1993) Human Biology and Health. Englewood Cliffs NJ: Prentice Hall.

2. Letsky EA, Leck I, Bowman JM. (2000) Chapter 12: Rhesus and other haemolytic diseases. Antenatal & neonatal screening (2nd ed.) Oxford University Press.

3. Table of blood group systems. (2008) International Society of Blood Transfusion.