blood-typing

How pathology keeps our blood supply pumping

No one wants to be in a situation where they need a blood transfusion but unfortunately many people need donated blood in Australia every day.

A person may need donated blood for several reasons. The most well-known of these is blood loss due to an accident or surgery but there are also other conditions such as treatment for cancer which could leave someone’s blood depleted.

Donated blood is separated into its components, red cells, white cells, platelets and plasma and these are used directly to treat patients and can also be made into vaccines and other medical products.

Pathology testing is used to determine a person’s blood type and donated blood is screened for a number of diseases, these are:

  • HIV 1 & 2
  • Hepatitis B and C
  • Syphilis
  • Human T-cell lymphotropic virus (HTLV)
  • Cytomegalovirus (CMV)
  • Some blood is also tested for malaria

As well as testing for antibodies, which is the standard type of testing for these viruses, in the cases of HIV-1 and hepatitis B and C, the Blood Service also uses Nucleic Acid Testing (NAT). This type of testing looks for the presence of the actual virus via its DNA (or RNA).

A test which looks for antibodies is based on the body’s response to the virus, but during the earliest stages of infection a person’s body may take time to respond and produce antibodies. This means that NAT testing adds an extra layer of protection and further reduces the risk of infected blood entering the blood supply.

So what happens when the blood gets to hospital?

Pathology is at the interface between the Blood Service and the patient. Pathology laboratories that service trauma centres or hospital wards likely to need to transfuse patients (i.e. maternity, surgical, oncology wards) will order units of blood from the Blood Service that they keep to hand in large fridges.

When a doctor requests a transfusion, they will send a tube of blood from the patient urgently to the laboratory. The pathology staff will then check the compatibility of the patient blood with donated units – a process called cross-matching.

Cross-matching involves mixing a small sample of the patient’s blood together with a small sample taken from the donated blood unit and watching what happens. If the mixed blood clumps together, it cannot be transfused. If it mixes together without any clumping, it is can be used.

So what causes this clumping? Many people are familiar with the terminology of ABO blood typing, and Rhesus blood typing. For example, O+ or B-. These refer to antigens and antibodies in the bloodstream. The ABO and Rhesus antibodies are the most significant systems of antibodies in our blood. But beyond these are a vast array of antibodies that are less-well known, but can cause complications if the wrong blood is transfused.

Every single unit that is transfused in Australia is carefully assessed by pathology staff to make sure that none of these antibodies react with the patient’s blood. Any laboratory that provides transfusion services is subject to incredibly strict quality control checks and all staff must be fully trained.

As well as the rigour of testing and cross matching, Australia’s blood supply is also amongst the safest in the world because of the restrictions placed on who can donate.

Most people aged between 16 and 70 are eligible to give blood, however people who lived in the UK for more than 6 months between 1980 and 1996 cannot donate. The reason for this is human variant Creutzfeldt-Jakob disease (vCJD). This is the human form of ‘mad cow disease’ and there is currently no way to screen blood for it, which is why people who may be at risk of carrying the disease are excluded from giving blood.

Although blood transfusions are still considered safe and in many cases are necessary to save a person’s life, concerns have been raised more recently that doctors must be cautious in how they approach transfusions, as they still have some risks for patients.

Pathology testing is vital in helping doctors to determine a person’s transfusion needs (such as looking at haemoglobin levels) as well as identifying preventative measures; for example treating underlying anaemia prior to surgery, which could mean a patient does not need donated blood.

Image credit: Royal College of Pathologists of Australasia