Uninterpretable cerebrospinal fluid absorbance scan caused by doxycycline therapy
The revised national guidelines for the analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage (UK) provide a framework for the analysis of cerebrospinal fluid samples for the purpose of investigation of subarachnoid haemorrhage. In principle, as long as samples are collected and analysed according to the guidelines, any absorbance scan thus obtained ought to be amenable to interpretation. The case presented involves a cerebrospinal fluid sample with an absorbance scan which could not be interpreted with the guidelines. An archive search for similar cases suggested interference from doxycycline therapy as the cause. Doxycycline was confirmed to be the cause through experimental in vitro reproduction of the interference. Difficulties arising from this interference are discussed. It is hoped that a future version of the guidelines may mention, and propose a means of dealing with, the issue of doxycycline interference.