A Barr body (see image) appears as a small drumstick-like projection on one of the lobes of some neutrophils in individuals with XX sex chromosomes or XXY (Klinefelter syndrome). Barr bodies are attached to the nuclear lobe by a single narrow stalk, distinguishing them from other thicker projections, sometimes called "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 peripheral blood smear. In rare chromosome disorders with three or more X chromosomes 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 metastasized malignant tumors.
Recognition of a Barr body in a neutrophil is essential to avoid reporting it as abnormal (unless two or more per neutrophil are seen). The Barr body is considered non-pathological unless associated with rare chromosome disorders.
