The double-ring test is clearly shown in this photo. It is also known as the ring sign or halo sign. The patient was brought following an injury to the head and was bleeding moderately from the nose but the blood was more watery than normal. CSF rhinorrhea was suspected.
The dextrose stick test was positive to the sample and when placed on a filter paper, we got an inner ring of blood and a halo, followed by an outer ring of CSF. Though this has been a classical medical test, it is not 100% reliable.