In a patient suspected of having a subarachnoid hemorrhage, what finding from a lumbar puncture would support the diagnosis?

The presence of xanthochromia in the cerebrospinal fluid (CSF) is a significant finding that supports the diagnosis of a subarachnoid hemorrhage (SAH). Xanthochromia refers to the yellowish discoloration of the CSF, which is typically caused by the breakdown of red blood cells (RBCs) and the subsequent release of bilirubin. This process usually occurs several hours to a few days after the hemorrhage, as the blood in the CSF undergoes lysis and metabolization.

In cases of SAH, when blood enters the subarachnoid space, it can lead to the appearance of xanthochromia on CSF analysis. This finding is especially important when the initial CT scan does not clearly show the hemorrhage, and it allows clinicians to confirm or strongly suggest the presence of bleeding within the subarachnoid space.

Other CSF findings, such as RBC counts or glucose levels may provide some insights, but they are less definitive for diagnosing SAH. A declining RBC count in subsequent collection tubes suggests a procedure-related issue or may indicate that the blood present was due to a traumatic tap, rather than an SAH. Meanwhile, low glucose levels could indicate other conditions