In regard to the halo test, a positive indicator for cerebrospinal fluid (CFS) when tinged with blood will show the following when dropped on an absorbent tissue:
A. A single ring with a darker center spot containing blood components surrounded by a light halo of CFSCopious clear drainage from the nose or ear makes the diagnosis of cerebrospinal fluid ( CSF) leakage obvious. Often, however, the drainage may be discolored with blood or small in volume if some drains into the throat. The halo test can help differentiate. Allow a drop of the fluid to fall on an absorbent surface such as a facial tissue. If blood is mixed with CSF, the drop will form a double ring, with a darker center spot containing blood components surrounded by a light halo of CSF. If this test is indeterminate, the fluid can be sent for beta-2 transferrin testing, a carbohydrate-free isoform of transferrin exclusively found in the CSF.