Unrecognized Preanalytical Problem with the Spectrophotometric Analysis of Cerebrospinal Fluid for Xanthochromia

Abstract

The primary diagnostic test for subarachnoid hemorrhage (SAH)1 is a computed tomography scan, but because SAH is found in a small percentage of patients with negative computed tomography results, lumbar puncture (LP) and spectrophotometric analysis of cerebrospinal fluid (CSF) for xanthochromia are still needed to make decisions about angiography (1). Oxyhemoglobin (O2Hb) is released from erythrocytes (RBCs) in the CSF in vivo and converted to bilirubin in the leptomeninges in a time-dependent process. Although the trauma of LP frequently produces RBCs in CSF and RBC lysis leads to the presence of O2Hb, no bilirubin is formed in such cases. The presence of bilirubin is considered the most specific sign of SAH, and a LP is recommended 12 h after the appearance of symptoms to test for the presence of bilirubin(2)(3). O2Hb and bilirubin have absorbance peaks at 413–415 nm and 450–460 nm, respectively, but because of the overlap in absorbance wavelengths with O2Hb, bilirubin is preferentially measured at 476 nm(2)(3)(4). Nevertheless, avoidance of hemolysis ex vivo will improve the analysis of bilirubin in CSF and may make O2Hb a more reliable marker of bleeding. We conducted experiments to elucidate why RBCs lyse in CSF. A CSF pool …