Blood volume
This test measures the volume of red cells in the whole body and compares this to normal values. This is useful for inpatients who may have too many red blood cells or not enough plasma. It is important to inform the department before the test, if any blood has been taken from the patient in the previous four weeks.
When the patient arrives, a blood sample is taken from a vein in their arm. This blood sample is sent to the laboratory where a small amount of radioactivity is attached to the red cells.This takes about half an hour, after which time the blood sample is returned and reinjected into a different vein in the patient's arm. After a further 30 minutes, another blood test is taken from the patient's arm. This second sample can then be measured to calculate the proportion of radioactive cells present in it.
There are no side effects to this test and the injections will feel just like a normal blood test. After the last blood test has been taken, the patient is able to go home. The results of the test will be calculated and a written report will be sent to the referring doctor.