Explain the Radioactive Red Blood Cells

In order to make red blood cells radioactive, tagging of red blood cells with radioactive chromium (⁵¹cr) is done. A small quantity of ⁵¹cr is mixed with a few milliliters of blood removed from the person and this is incubated at 36°C for half an hour or more. After this time, most of the ⁵¹cr will have entered the red blood cells, but to remove the extra chromium from the mixture, the red blood cells are washed with saline. The total content of ⁵¹cr is then determined with a Geiger or scintillation counter (apparatus for measuring the total number of radioactive disintegrations occurring in the sample per minute). Then the radioactive cells are re-injected in the person. After mixing in the circulatory system for approximately 10 minutes, blood sample is taken from the circulatory system, and the radioactivity in this blood is determined, using dilution formula given above in dilution principle. Then actual volume is calculated i.e.

Actual blood volume = 1.1 x Measured blood volume