The measurement of total body potassium by ⁴⁰K takes place in a specially shielded room. The door must be closed throughout the procedure to help minimize outside radioactive interference. The test normally takes 15 minutes.

To make the test more comfortable, patients can watch TV or listen to music.

Patients usually change from street clothes. Clothing may contain dust particles with significant background contamination. Jewelry is also removed, since metals may contain trace contaminants.

Patients do not need to fast before undergoing a whole body count. Most foods contain ⁴⁰K in the same concentrations as in the body.

The procedure requires the patient to lie still throughout the test, but there is no noise or movement by the machine. A whole body count is a completely non-invasive process.

Spectrum from a potassium measurement shows a strong peak from 40K