If a CSF sample is yellow, what does this indicate?

• A. Increased glucose
• B. Bacterial growth
• C. Xanthochromia from RBC breakdown
• D. Decreased protein

Answer: (C)

Yellow CSF indicates xanthochromia, which arises when red blood cells in the CSF break down and release heme that is converted to bilirubin. This yellow-orange tint signals that blood has been present in the CSF for some time, most commonly from a bleed into the subarachnoid space (such as subarachnoid hemorrhage). It reflects a prior hemorrhagic event rather than changes in glucose or protein levels. In contrast, bacterial infection typically makes the CSF turbid rather than simply yellow, and changes in glucose or protein don’t by themselves produce a yellow color.