Automated measurement of cerebrospinal fluid bilirubin in suspected subarachnoid hemorrhage.

Abstract

Early detection of subarachnoid hemorrhage (SAH) can improve clinical outcome (1). After hemorrhage into the cerebrospinal fluid (CSF), erythrocytes lyse, releasing oxyhemoglobin, which is metabolized to bilirubin. The detection of increased CSF bilirubin is the basis for the laboratory identification of in vivo hemorrhage (2). Guidelines for the detection of CSF bilirubin in suspected SAH have recently been published (2). In the guidelines, the preferred method for detection of bilirubin is spectrophotometric scanning, with the net bilirubin absorbance (NBA) calculated according to Chalmers’ modification (3)(4). The procedure is not necessarily ideally suited for a clinical laboratory environment, and most hospital laboratories in the United States still use subjective visual inspection to identify CSF xanthochromia (5). The visual interpretation of spectrophotometric spectra is also subjective (which complicates clinical interpretation), although an iterative model has been proposed to circumvent this problem (6). We evaluated the measurement of CSF bilirubin on an automated instrument, using the Jendrassik–Grof method, calibrated to measure lower concentrations. We report our experience with this method and compare the results with those of spectrophotometric scanning. Spectrophotometric scanning was performed according to the guidelines (2), and a cutoff value of >0.007 for NBA was defined as positive. In all positive cases, a corrected value was calculated using the CSF and serum protein concentrations and the serum bilirubin concentration (2). Bilirubin was measured by a modification of our routine serum bilirubin assay, which consists of an in-house method on an Aeroset analyzer (Abbott Laboratories). The method is based on the Jendrasik–Grof principle as described by Doumas et al. (7), with a modification of the diazo reagent according to Chan et al. (8). To measure bilirubin at the concentrations typically found in CSF, we increased the ratio of sample to reagent …