A Barr body (see image) appears as a small drumstick-like projection on one of the lobes of some neutrophils in females. Barr bodies are attached to the nuclear lobe by a single narrow stalk, which distinguishes them from other thicker projections, sometimes referred to as "clubs." Since Barr bodies are the morphological expression of the inactivated X chromosome, Barr bodies (one per neutrophil) can be seen in up to 3% of the neutrophils on a female's peripheral blood slide. In rare chromosome disorders in which three or more X chromosomes are present, two to three Barr bodies per neutrophil can be seen.
Barr bodies must also be distinguished from hair-like projections sometimes seen in the band form, following irradiation or in patients with a malignant tumor that has metastasized.
Recognition of a Barr body in a neutrophil is important in order to avoid reporting it as abnormal (unless two or more per neutrophil are seen). The Barr body is considered nonpathological unless associated with rare chromosome disorders.