Despite the many advances in medical science, there is still no substitute for transfused blood products to sustain life during surgery if you are unfortunate enough to have an accident causing severe bleeding. Donated blood is equally important during planned major surgery and for other conditions such as anaemia. A heart operation uses an average of six pints of red blood cells and six pints of platelets. This year, in New Zealand, 150,000 whole blood units will be needed to meet clinical needs (one unit is about 470ml, or just under a pint). So what is it all about?

Blood and blood groups

Whole blood comprises four main components:

• Red blood cells - contain haemoglobin, an iron-containing protein that carries oxygen throughout the body
• White blood cells - prevent and fight infection
• Platelets - aid the clotting process by sticking to the lining of blood vessels
• Plasma - the liquid portion of blood; a protein-salt solution in which the other cells are suspended (plasma is 90 per cent water and constitutes about 55 per cent of blood volume).

Of these, only the white blood cells tend not to be used for transfusion because of their short life span. The other components can be used singly or as a whole blood transfusion.

Chemicals on the surface of red blood cells differ between people and they have been classified accordingly. The two main ways of classifying blood for transfusion is by the person's group (ABO system) and their type - Rhesus (Rh) system. These classifications are important and matching of donor-recipient types prevents immune-based reactions from blood transfusions.

Within the ABO system, a person can be one of four groups - O, A, B or AB, while in the Rh system they can be either Rh positive or Rh negative. Each system is inherited independently of the other, so there are eight main blood groups. In terms of compatibility for transfusion, for example, an A negative patient may receive blood from an O negative or an A negative donor.

A further result of this matching is that, in an emergency, the red cells of type O negative donors can be transfused to people with any blood type; as such, they are referred to as 'universal donors'. This obviously creates great demand for type O blood in general. About 50 per cent of New Zealanders are type O, hence it is particularly important that these people become donors. Conversely, those with type AB+ blood ('universal receivers') can receive any of the eight types of blood.

	Donors
	Type	O-	O+	B-	B+	A-	A+	AB-	AB+
Receivers	AB+
	AB-		-		-		-		-
	A+			-	-			-	-
	A-		-	-	-		-	-	-
	B+					-	-	-	-
	B-				-	-	-	-	-
	O+			-	-	-	-	-	-
	O-		-	-	-	-	-	-	-

What is the blood used for?

Blood may be transfused as whole blood or as one of its components. Few patients require whole blood, so patients generally receive only that portion specifically needed. This is referred to as 'blood component therapy', and it allows several patients to benefit from one unit of donated whole blood. Up to four components can be derived from one unit of blood, some of which include:

• Red blood cells - used for the treatment of anaemia and bleeding after trauma and surgery
• Frozen red cells - used for long term storage of rare blood groups
• Filtered red cells - for patients who have antibodies against white cells
• Fresh frozen plasma - used to treat patients who have bleeding problems
• Platelets - for control of haemorrhage, often used in patients with leukaemia.

Donated red blood cells normally have a life of 35 days, or they may be treated and frozen for extended storage for up to 10 years.

In addition to these cell components, the following protein and immune system products are just some of those processed in Australia from plasma donated by New Zealand donors for use in New Zealand patients:

• Normal immunoglobin - for temporary protection against measles, rubella and hepatitis A
• Specific immunoglobins - for treatment of tetanus or to prevent hepatitis B, chicken pox or haemolytic disease of the newborn in patients at risk
• Prothrombinex - contains concentrated clotting factors and can be used for the treatment of haemophilia B
• Intragram-p - used to boost the immune system following bone marrow transplant and for immune deficiencies
• Anti-D - prevents Rhesus disease in the newborn, which results in the mother developing antibodies against her baby's blood
• Factor VIII - used in the inherited bleeding condition haemophilia A.

To get a better idea of what it means to have these blood products available take time to read some of the personal stories of recipients in New Zealand and Australia. For a fuller glossary of blood terms click here.

Who can donate blood?

The New Zealand Blood Service (NZBS) is the organisation responsible for the collection, storage and distribution of blood products in New Zealand. While striving to maintain adequate national supplies it must ensure that the blood donated is in no way harmful to the recipient, and that donating does not harm the donor.

From the donor's point of view, you are a 'fit' to give blood if you:

• are aged over 16 years and under 60 years (existing donors can donate until they are 71)
• weigh over 50kg
• are not engaging in any high risk behaviour that may expose you to human immunodeficiency virus (HIV) or other viruses
• are in good health
• have not lived in the UK, France or the Republic of Ireland for a total of six months or more between 1980 and 1996 - unfortunately you will be permanently deferred from donating blood in New Zealand you have lived in these countries for this time. For eligibility criteria click here. 
  

A finger prick blood test for haemoglobin level is also made to ensure the donor is not anaemic.

Screening to ensure a safe blood supply

The NZBS employs the latest tests to screen for transmissible diseases such as hepatitis B, hepatitis C and HIV, and collaborates with overseas blood services to develop effective policies in this area. (The donor is not at risk of infection because new needles and collection equipment are used for each donor and are then discarded.)

To further protect the recipient, the NZBS asks each potential donor at each visit to complete a confidential questionnaire covering their health history, lifestyle and recent travel. To view the questionnaire as a pdf file, click here. This will give you an idea of the questions asked but trained medical staff are on hand at the collection centre to assist with completing the form. A 'yes' answer to a question MAY NOT prevent you from giving blood. These requirements are for medical reasons and the NZBS makes no moral judgements about the activities of any potential donor.

The NZBS practises a 'safety first' policy. In February 2000, this resulted in the service asking 12,000 existing donors who had lived in the UK for six months or more between 1980 and 1996 not to volunteer for donations. This was a preventative measure designed to eliminate the extremely remote risk of variant Creutzfeld-Jakob disease (possibly a human form of bovine spongioform encephalopathy, BSE or 'mad cow disease') entering the blood supply. To put this in perspective, less than 100 cases of this human form of the disease have been reported in Europe (and none in New Zealand), and there is still no evidence to suggest the disease can be transmitted by transfusion. This particular policy helps ensure that New Zealand continues to have one of the safest blood supplies, but it increases the need for new donors to come forward.

Becoming a donor

Let's be honest, we'd all choose not to have a needle stuck in our arm for the sake of it but, as it's done by trained medical staff, it really does rate quite low on the absolute scale of discomfort. Moreover, the actual collection of blood takes less than 10 minutes and the whole visit is over in less than an hour. There are four stages to consider if you are thinking of becoming a donor for the first time: preparation, registration, donating and recovery.

Preparation

Wait until you are fully recovered from any cough, cold or sore throat, and make sure you have had plenty to eat and drink before making your appointment. Do not take aspirin for 72 hours before your appointment. If you have had an operation, a tattoo or body piercing, a course of antibiotics or are currently taking medication or have been overseas or become pregnant, contact the NZBS to clarify whether you should attend.

Registration

When you arrive, check in at the reception desk and complete the donor questionnaire. These questions are designed to identify those individuals whose behaviour puts them at an increased risk of acquiring blood-borne diseases such as HIV, hepatitis and other infectious diseases. You will then have a confidential interview with a member of the donor team who will also check your haemoglobin levels (using a finger prick test) and answer any questions you may have. This is to make sure that it is both safe for you to donate and for your blood to be transfused to a patient.

Donating

Take a seat on one of our comfortable chairs. Your arm will be cleaned and a single use, sterile needle will be inserted into a vein in your arm, with slight discomfort only as the needle goes in. Then blood is collected in a sterile bag (around 470ml). The actual donation process is relatively simple and is pain-free. The needle is removed and a bandage is applied.

Recovery

After donating, rest seated for around 10 minutes. When you are ready, you will be invited to have refreshments in the recovery area. The donor team likes to keep an eye on you for a few more minutes to make sure that you are feeling OK before you leave.

The New Zealand Blood Service

The New Zealand Blood Service (NZBS) was created on 1 July 1998 to ensure the supply of safe blood and blood products and to develop an integrated national blood transfusion service for New Zealand (a "vein-to-vein" service). The NZBS operates donor centres throughout the country. The service also has mobile collection units. To find out about these contact your regional centre, check the local newspaper or visit their website at www.nzblood.co.nz

Original material sourced from the New Zealand Blood Service, and edited by everybody, May 2008.