Perls stain is used in pathology to detect any ferric overload. The iron, fixed in the hemosiderin, is colored blue by Prussian blue, the nuclei are highlighted by the nuclear red.

Iron-bearing red blood cells are called siderocytes, and erythroblasts (precursors of red blood cells) that carry iron are called sideroblasts.

Perls stain is used in particular in the diagnosis of iron deficiency (iron deficiency) and inflammatory syndromes. The absence of iron in erythroblasts and macrophages is characteristic of iron deficiency. The presence of iron in macrophages and its absence in erythroblasts is very suggestive of an inflammatory syndrome. In some hereditary or acquired anemias, known as sideroblastic anemias, it makes it possible to detect iron inclusions of characteristic form in the sideroblasts (erythroblasts of the bone marrow carrying ferric inclusions), which are abnormally arranged around the nucleus.