The 'ring sign': is it a reliable indicator for cerebral spinal fluid?

Abstract

To study the development of a ring sign when blood is mixed with various fluids. One drop of blood and one drop of either spinal fluid, saline, tap water, or rhinorrhea fluid were placed simultaneously on filter paper, and the specimens were examined after ten minutes for the development of a ring. A variety of filter paper agents were used, including standard laboratory filter paper, paper towels, coffee filters, and bed linens. All fluids, when mixed with blood, gave rise to a ring sign; blood alone did not. The type of filter paper did not affect the development of a ring. In this experimental setting, the ring or halo sign is reliable for detecting cerebrospinal fluids but is not exclusive for cerebrospinal fluid.