Measurement in a specified sample of kidney tissue of the amount of corpuscular or electromagnetic radiations emitted consequent to nuclear disintegration of a radioactive isotope which is replacing a stable chemical element in a compound that has been introduced into lymphocytes (small agranulocytic leukocytes that originate from fetal stem cells and develop in the bone marrow) rendering them able to be followed or tracked through the body. Kidney is the organ which functions to maintain proper water and electrolyte balance, regulate acid-base concentration, and filter the blood of metabolic wastes.