When cerebrospinal fluid is placed on a white absorbent paper, which distinguishing feature helps differentiate it from other fluids?

When cerebrospinal fluid is placed on a white absorbent paper, which distinguishing feature helps differentiate it from other fluids?

• A. Halo sign
• B. Ring test
• C. Diffusion pattern
• D. Color change

Answer: (A)

The property being tested is how CSF behaves on an absorbent surface. When a drop of CSF is placed on white paper, it typically forms a pale, circular ring around the central stain—a halo. This halo results from the way CSF diffuses through the paper due to its composition and relatively low protein content, creating a distinctive peripheral diffusion that most other fluids don’t produce. Because blood, urine, or other secretions don’t create that same halo pattern, this halo sign helps differentiate CSF from those fluids. In practice, observing a halo supports CSF presence, though confirmatory tests (like specific protein markers) can be used if needed.

The property being tested is how CSF behaves on an absorbent surface. When a drop of CSF is placed on white paper, it typically forms a pale, circular ring around the central stain—a halo. This halo results from the way CSF diffuses through the paper due to its composition and relatively low protein content, creating a distinctive peripheral diffusion that most other fluids don’t produce. Because blood, urine, or other secretions don’t create that same halo pattern, this halo sign helps differentiate CSF from those fluids. In practice, observing a halo supports CSF presence, though confirmatory tests (like specific protein markers) can be used if needed.