Rosh Emergency Medicine Practice Test

In a patient suspected of having a subarachnoid hemorrhage, which laboratory finding from a lumbar puncture would be expected?

1. Elevated immunoglobulin G index

2. Low glucose level

3. RBC count that declines with each subsequent collection tube

4. Xanthochromia

The correct answer is: Xanthochromia

In the context of a suspected subarachnoid hemorrhage (SAH), the presence of xanthochromia in the cerebrospinal fluid (CSF) obtained via lumbar puncture is a key indicator. Xanthochromia refers to a yellowish appearance of the CSF, which occurs when there is the breakdown of red blood cells and subsequent release of bilirubin. This is typically seen several hours after a hemorrhagic event, as the red blood cells lysate and release intracellular components. The detection of xanthochromia is significant because it helps differentiate between SAH and other causes of blood in the CSF, such as a traumatic tap during lumbar puncture. In cases of traumatic taps, the CSF would often show red blood cells, but the color of the fluid would remain clear unless there is significant contamination. Therefore, finding xanthochromia in the CSF aligns with the diagnosis of SAH, confirming the presence of prior hemorrhage. In contrast, other laboratory findings stated in the choices do not correlate specifically with SAH. For instance, an elevated immunoglobulin G index is more relevant in the context of demyelinating diseases or infections like multiple sclerosis. A low glucose level is typically