In a dog with vitamin B6 deficiency, there are numerous siderocytes (arrows), indicating accumulation of iron. However, red blood cells are also hypochromic (and fragmenting), which typically indicates an iron deficiency anemia. In addition, iron concentrations and percentage saturation of transferrin in serum were normal. The dichotomy of iron deficient red blood cells accumulating cytoplasmic iron (presumably in mitochondria) reflects a functional iron deficiency due to inhibition of heme synthesis or mitochondrial dysfunction. In this case, the siderocytes and iron deficiency anemia were due to vitamin B6 deficiency as vitamin B6 concentrations were very low and the hematologic changes resolved with multiB vitamin supplementation (modified Wright’s stain, 100x magnification)
