This review delineates the subcellular distribution, biochemical characteristics, and metabolic functions of
5'-nucleotidase (5'NT), summarizes the analytical biochemistry of 5'NT, and assesses the clinical significance of 5'NT determinations in body fluids, cells, and tissues. Salient aspects of the clinical biochemistry of 5'NT, discussed herein, are as follows: (A) Serum 5'NT activity is generally elevated in
hepatobiliary diseases, especially with intrahepatic obstruction, but, unlike serum
alkaline phosphatase, serum 5'NT activity is not increased in infancy, childhood, pregnancy, or osteoblastic disorders. (B) In
cancer patients, elevated serum 5'NT activity does not always indicate hepatobiliary involvement; in some cases, 5'NT may be released into serum from the primary
tumor or local
metastases. (C) Genetic deficiency of erythrocyte
pyrimidine 5'NT activity is a common cause of hereditary non-spherocytic
hemolytic anemia. (D) Acquired deficiency of erythrocyte
pyrimidine 5'NT activity occurs in patients with
beta-thalassemia and
lead poisoning. (E) 5'NT activity is low in circulating monocytes, increases markedly upon their differentiation to tissue macrophages, and subsequently diminishes during macrophage activation. (F) Lymphocyte ecto-5'NT activity, a plasma membrane marker of cell maturation, is generally low in immunodeficiency states, and undergoes characteristic changes in patients with certain
lymphomas and
leukemias.