What is blood?

Blood is a fluid that transports oxygen and nutrients to the cells of animals and carries away waste products. In many animal species, blood also carries hormones and disease-fighting substances. Humans are complex multicellular organisms and the average adult human has about five litres of blood.

How is it useful in forensic science?

Blood left at a crime scene is a valuable clue in solving crime. Blood collected at a crime scene is sent to a laboratory for identification. Every person has one of 4 basic blood types: A, B, AB or O. Each blood type may then have a further classification, positive or negative.

As you can see from the table, blood type O is very common. A blood test can help identify a possible suspect, but might not absolutely identify the suspect as they may be one of many with that blood type. Finding an AB blood type is useful as it eliminates many suspects.

Frequency of blood groups in the Australian population
A positive: 31% B positive: 8%

AB positive: 2%

O positive: 40%
A negative: 7% B negative: 2% AB negative: 1% O negative: 9%

Blood groups in the Australian population shown in a pie chart

The blood type percentages shown in the table above are for the Australian population. These relative frequencies do change with different racial groups throughout the world.

Antibodies and antigens

Antibodies and antigens play an important part in identifying blood.
More information and quiz

How are samples collected?

Blood samples can easily be found at a crime scene and collected. If the blood covered material can be removed from the crime scene it is clearly labelled and then taken away to be tested. If the blood covered materials cannot be moved, then a swab can be used to collect the blood.

How are samples analysed?


Large blood samples can be analysed by a simple test like the one you are about to do here!

Once the blood type of a sample has been determined it can be used to eliminate a suspect or include them as a possibility. Note that a blood test does not match the blood, just the blood type.
Identify a blood type

Did you know?

By using a chemical called luminol, blood that is not visible to our eyes can be seen.

All about blood  by Australian Red Cross <>

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The Department of Education would like to thank Tasmania Police, and in particular Tasmania Police Forensic Services, for their assistance in the making of these materials.