Use of isotopes in the diagnosis of hematopoietic disorders.

Isotopes of iron have been paramount in clinical tracer studies of hematopoiesis. Kinetics of disappearance from plasma, appearance in circulating erythrocytes, and localization in general areas of bone marrow, spleen, and liver were early revealed by gamma-/beta-emitting Fe-59 with note of characteristic differences of kind and degree of dysfunction among various anemias. Findings have helped in management (e.g., decisions about splenectomy). Positron/gamma-emitting Fe-52 (better for imaging) has provided more detail on marrow expansion and erythropoietic relocation. Other gamma-emitting tracers of hematopoiesis have been In-111 (linked to transferrin) and technetium 99m (Tc-99m) colloids (localizing to reticuloendothelial cells, which have close association with blood cell progenitors), but Fe-52 has proved to be more accurate for recognition of erythropoiesis. Occasional diverse heterotopic sites of hematopoiesis beyond spleen and liver in states of bone marrow disease have posed diagnostic challenges and also raised questions about migration and/or activation of stem cells. Studies of granulopoiesis utilize Tc-99m--labeled leukocytes or Tc99m-labeled antibodies to circulating and progenitor white cells. Iron-deficiency anemias due to malnutrition, malabsorption, blood loss, or special need are explored by dual study (oral vs intravenous) with radioactive (Fe-59, Fe-55) or stable (Fe-54, Fe-57) iron isotopes, which can guide dietary supplementation. Tests for B-12 deficiency in pernicious anemia or malabsorption with radioisotopes of cobalt (Co-57, Co-58) have been upgraded in sensitivity and scope. Rates of oxidation to expired carbon dioxide from particular carbon (radioactive C-14 or stable C-13)--labeled compounds can test B-12 or folic acid deficiencies or gastric infestation as causes of megaloblastic anemias.