Nursing care
Why a halo sign suggests a CSF leak after head injury, and what the nurse does next
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
When bloody fluid from the nose or ear contains cerebrospinal fluid, the thin, clear CSF spreads farther across gauze or linen than the red cells. A central blood spot with a pale outer ring forms, called the halo sign. It raises suspicion of a skull base fracture, but it is unreliable alone, so the nurse reports it.
Follow the fluid from a torn dura to the gauze
Cerebrospinal fluid surrounds the brain inside the dura. A fracture of the base of the skull can tear the dura and open a path from the CSF space into the nose, sinuses or middle ear. CSF then leaks out as clear, watery drainage from the nose or ear, often mixed with blood when it follows trauma.
When that mixture drips onto gauze, a pillowcase or filter paper, the components separate as they soak in. Red cells stay near the point of contact, while the thinner, clear CSF wicks outward faster and farther. The result is a red or dark centre surrounded by a lighter, yellowish ring. That ring is the halo, also called the ring or double-ring sign.
Why the halo sign raises suspicion but does not confirm
The halo sign was widely taught as a bedside predictor of CSF leak, but a specialist review describes it as unreliable, because many fluids mixed with blood, such as tears, saliva, saline or nasal mucus, can form a similar ring. A positive halo therefore means a possible leak to report, not a confirmed diagnosis.
Glucose testing of the fluid has also largely fallen out of favour as a confirmatory test because results are affected by blood and other conditions. Laboratory detection of beta-2 transferrin, a protein variant found in CSF, is the current reference test, with imaging used to locate the leak. Other clues include clear, watery, one-sided drainage that worsens when leaning forward, and a salty taste.
Expected findings versus concerning trends
After a head injury, bruising behind the ear (Battle sign), bruising around both eyes (raccoon eyes), blood behind the eardrum and clear fluid from the nose or ear all point toward a skull base fracture. Any of these with drainage should be documented and reported. A small amount of blood from a nasal or scalp wound alone is less specific.
The concerning trends are increasing clear drainage, a falling level of consciousness, worsening headache, and signs of infection such as fever, neck stiffness or a new headache days later. An open path between the nose or ear and the brain coverings allows bacteria to reach the meninges, so meningitis and other intracranial infections are the main delayed risks of an untreated leak.
Turn the mechanism into nursing actions
Let the fluid drain freely. Place a loose sterile pad or dressing under the nose or over the ear to collect and observe it, and do not pack the nostril or ear canal or try to clean inside it. Note colour, amount and whether a halo forms on the pad, then report the finding promptly so the team can decide on confirmatory testing and imaging.
Many units avoid nasal suctioning and nasal tubes when a skull base fracture is suspected; follow orders and local protocol. Teach the patient not to blow the nose or strain, because pressure changes can worsen the leak or push bacteria inward. Continue neurological observations and report fever or neck stiffness, which may signal infection.
Work through a hypothetical exam-style scenario
Imagine a hypothetical patient after an assault who has bruising behind the right ear and pink-tinged fluid dripping from that ear. On the gauze, a red centre is surrounded by a pale yellow ring. The options are to pack the ear with gauze to stop the drainage, to irrigate the ear canal, or to apply a loose sterile pad and notify the provider.
A loose sterile pad and prompt notification is the strongest answer. Packing blocks the outflow and can trap fluid and bacteria, and irrigation introduces fluid into a possible path to the brain coverings. The tested reasoning is that a halo around blood suggests CSF from a skull base fracture, which needs confirmation and infection protection rather than local treatment.
Sources and further reading
Europe PMC: Multimodal diagnosis of cerebrospinal fluid rhinorrhea (review). Halo sign described as unreliable, glucose testing out of favour, beta-2 transferrin as reference test, clinical clues and meningitis risk.
MSD Manual Professional: Traumatic brain injury. Basilar skull fracture signs: CSF rhinorrhea and otorrhea, haemotympanum, Battle sign and raccoon eyes.
NHS: Head injury and concussion. Clear fluid from the ears or nose and bruising behind the ears as emergency signs after head injury.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our neurological practice questions are the closest set to what this page covers.
Common questions
What does a halo sign look like on gauze?
A spot of blood in the centre surrounded by a lighter, yellowish ring. The clear CSF spreads farther through the fabric than the red cells, forming the outer ring.
Does a positive halo sign confirm a CSF leak?
No. Tears, saliva, saline and other fluids mixed with blood can produce a similar ring. Laboratory testing for beta-2 transferrin and imaging are used to confirm and locate a leak.
Why should a patient with a suspected CSF leak avoid blowing the nose?
Blowing the nose and straining change pressure in the head and sinuses. That can enlarge the leak or push bacteria toward the meninges, raising the risk of meningitis.