There are two basic meanings to the phrase 'protein in blood'.

The first relates to the fact that blood actually carries protein around the body- almost shipping it to wherever it is needed e. g. the muscles etc.

Sometimes blood is tested for protein by doctors. This is known as a TP test and is actually a blood plasma test. The test reveals the protein levels in the blood and can give information about how nutritionally sound we are i.e. if we are eating ok. This test can also check for any kidney or liver irregularities.

The second meaning of the phrase relates to the fact that there is red protein in the blood which carries oxygen ~ this is haemoglobin. Haemoglobin levels may be checked to see if the red protein cells are ok and if the blood has enough oxygen.

Sometimes protein can leak out from the blood and go into the urine system. This is known as proteinuria.