Blood Types

Although all blood is made of the same basic elements, not all blood is alike. In fact, there are eight different common blood types, which are determined by the presence or absence of certain antigens – substances that can trigger an immune response if they are foreign to the body. Since some antigens can trigger a patient's immune system to attack the transfused blood, safe blood transfusions depend on careful blood typing and cross-matching.

There are four major blood groups determined by the presence or absence of two antigens – A and B – on the surface of red blood cells:

• Group A – has only the A antigen on red cells (and B antibody in the plasma)
• Group B – has only the B antigen on red cells (and A antibody in the plasma)
• Group AB – has both A and B antigens on red cells (but neither A nor B antibody in the plasma)
• Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma)

There are very specific ways in which blood types must be matched for a safe transfusion: 

In addition to the A and B antigens, there is a third antigen called the Rh factor, which can be either present (+) or absent ( – ). In general, Rh negative blood is given to Rh-negative patients, and Rh positive blood or Rh negative blood may be given to Rh positive patients.

• The universal red cell donor has Type O negative blood type.
• The universal plasma donor has Type AB positive blood type.

O positive is the most common blood type. Not all ethnic groups have the same mix of these blood types. Hispanic people, for example, have a relatively high number of O’s, while Asian people have a relatively high number of B’s. The mix of the different blood types in the U.S. population is:

	Caucasians	African American	Hispanic	Asian
O +	37%	47%	53%	39%
O -	8%	4%	4%	1%
A +	33%	24%	29%	27%
A -	7%	2%	2%	0.5%
B +	9%	18%	9%	25%
B -	2%	1%	1%	0.4%
AB +	3%	4%	2%	7%
AB -	1%	0.3%	0.2%	0.1%

Some patients require a closer blood match than that provided by the ABO positive/negative blood typing. For example, sometimes if the donor and recipient are from the same ethnic background the chance of a reaction can be reduced. That’s why an African-American blood donation may be the best hope for the needs of patients with sickle cell disease, 98 percent of whom are of African-American descent.

It’s inherited. Like eye color, blood type is passed genetically from your parents. Whether your blood group is type A, B, AB or O is based on the blood types of your mother and father.

This chart shows the potential blood types you may inherit. 

Parent 1

AB

AB

AB

AB

B

A

A

O

O

O

Parent 2

AB

B

A

O

B

B

A

B

A

O

Possible blood type of child

O

X

X

X

X

X

X

A

X

X

X

X

X

X

X

B

X

X

X

X

X

X

X

AB

X

X

X

X

* Note: If you have questions about paternity testing or about blood group inheritance, your primary care physician should be able to provide you with an appropriate referral. Testing difficulties can cause exceptions to the above patterns. ABO blood typing is not sufficient to prove or disprove paternity or maternity.

• Facts about blood needs

• Every two seconds someone in the U.S. needs blood.
• More than 41,000 blood donations are needed every day.
• A total of 30 million blood components are transfused each year in the U.S.
• The average red blood cell transfusion is approximately 3 pints.
• The blood type most often requested by hospitals is Type O.
• The blood used in an emergency is already on the shelves before the event occurs.
• Sickle cell disease affects more than 70,000 people in the U.S. About 1,000 babies are born with the disease each year. Sickle cell patients can require frequent blood transfusions throughout their lives.
• More than 1.6 million people were diagnosed with cancer last year. Many of them will need blood, sometimes daily, during their chemotherapy treatment.
• A single car accident victim can require as many as 100 pints of blood.
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• Facts about the blood supply :

• The number of blood donations collected in the U.S. in a year: 15.7 million
• The number of blood donors in the U.S. in a year: 9.2 million
• Although an estimated 38% of the U.S. population is eligible to donate, less than 10% actually do each year.
• Blood cannot be manufactured – it can only come from generous donors.
• Type O-negative blood (red cells) can be transfused to patients of all blood types. It is always in great demand and often in short supply.
• Type AB-positive plasma can be transfused to patients of all other blood types. AB plasma is also usually in short supply.

• Facts about the blood donation process

• Donating blood is a safe process. A sterile needle is used only once for each donor and then discarded.
• Blood donation is a simple four-step process: registration, medical history and mini-physical, donation and refreshments.
• Every blood donor is given a mini-physical, checking the donor's temperature, blood pressure, pulse and hemoglobin to ensure it is safe for the donor to give blood.
• The actual blood donation typically takes less than 10-12 minutes. The entire process, from the time you arrive to the time you leave, takes about an hour and 15 min.
• The average adult has about 10 pints of blood in his body. Roughly 1 pint is given during a donation.
• A healthy donor may donate red blood cells every 56 days, or double red cells every 112 days.
• A healthy donor may donate platelets as few as 7 days apart, but a maximum of 24 times a year.
• All donated blood is tested for HIV, hepatitis B and C, syphilis and other infectious diseases before it can be released to hospitals.
• Information you give to the American Red Cross during the donation process is confidential. It may not be released without your permission except as directed by law.

• Facts about blood and its components :

• There are four types of transfusable products that can be derived from blood: red cells, platelets, plasma and cryoprecipitate. Typically, two or three of these are produced from a pint of donated whole blood – hence each donation can help save up to three lives.
• Donors can give either whole blood or specific blood components only. The process of donating specific blood components – red cells, plasma or platelets – is called apheresis.
• One transfusion dose of platelets can be obtained through one apheresis donation of platelets or by combining the platelets derived from five whole blood donations.
• Most donated red blood cells must be used within 42 days of collection.
• Donated platelets must be used within five days of collection – new donations are constantly needed.
• Plasma and cryoprecipitate are stored in frozen state and can be used for up to one year after collection.
• Healthy bone marrow makes a constant supply of red cells, plasma and platelets. The body will replenish the elements given during a blood donation – some in a matter of hours and others in a matter of weeks.
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• Facts about donors :

• The number one reason donors say they give blood is because they "want to help others."
• Two most common reasons cited by people who don't give blood are: "Never thought about it" and "I don't like needles."
• One donation can help save the lives of up to three people.
• If you began donating blood at age 17 and donated every 56 days until you reached 76, you would have donated 48 gallons of blood, potentially helping save more than 1,000 lives!
• Half of Red Cross donors male, and half are female.
• The American Red Cross accepts blood donations only from volunteer donors.
• Among Red Cross donors in a given year, 19 percent donate occasionally, 31 percent are first-time donors, and 50 percent are regular, loyal donors.
• Only 7 percent of people in the U.S. have O-negative blood type. O-negative blood type donors are universal donors as their blood can be given to people of all blood types.
• Type O-negative blood is needed in emergencies before the patient's blood type is known and with newborns who need blood.
• Forty-five percent of people in the U.S. have Type O (positive or negative) blood. This percentage is higher among Hispanics – 57 percent, and among African Americans – 51 percent.
• Only 3 percent of people in the U.S. have AB-positive blood type. AB-positive type blood donors are universal donors of plasma, which is often used in emergencies, for newborns and for patients requiring massive transfusions.

More about blood types : http://www.redcrossblood.org