CHARACTERIZATION OF IRON STATUS IN YOUNG-DOGS WITH PORTOSYSTEMIC SHUNT

Microcytosis is a common laboratory finding in dogs with congenital po rtosystemic shunt (PSS), although its pathogenesis is not yet understo od. Because the most common cause of microcytosis in dogs is absolute or relative iron deficiency, iron status was evaluated in 12 young dog s with PSS. Complete blood counting was done before surgical correctio n in all dogs, and in 5 dogs after surgery, by use of an automated hem atology analyzer. Serum iron concentration and total iron-binding capa city (TIBC) were determined coulometrically, and percentage of transfe rrin saturation was calculated. Erythrocyte protoporphyrin content was quantified by use of front-face fluorometry. Serum ferritin concentra tion was measured by use of ELISA. Serum ceruloplasmin content was det ermined colorimetrically (with p-phenylenediamine dihydrochloride as s ubstrate) as an indirect indicator of subclinical inflammation, which may result in impaired iron utilization. Special stains were applied t o liver (10 dogs; Gomori's) and bone marrow aspiration biopsy (7 dogs; Prussian blue) specimens for qualitative assessment of tissue iron co ntent. Nonpaired Student's t-tests were used to compare serum iron con centration, TIBC, percentage of transferrin saturation, and erythrocyt e protoporphyrin, ferritin, and ceruloplasmin concentrations in dogs w ith PSS with those in clinically normal dogs. AU dogs had microcytosis before surgery; microcytosis resolved in 3 dogs after surgical correc tion. Serum iron concentration and TIBC were significantly lower in PS S-affected dogs than in clinically normal dogs. Erythrocyte protoporph yrin, ferritin, and ceruloplasmin concentrations in PSS-affected dogs were not significantly different from those in healthy dogs. Excess ir on was not detected consistently in liver or bone marrow samples. Thes e results suggest that relative iron deficiency, perhaps associated wi th altered iron transport and not absolute iron deficiency, is related to microcytosis in dogs with PSS.