Audit can reduce inappropriate requests for cytological examination of cerebrospinal fluid

Cytological examination of cerebrospinal fluid (CSF) is indicated as part of an investigation of known or suspected central nervous system (CNS) malignancy (both primary and secondary). It may also play a role in the diagnosis of infections (e.g. fungal) not routinely picked up by commonly available microbiological or serological means. Studies indicate that the pre-test probability of receiving a diagnostic result from CSF cytology is virtually zero unless there is a history of malignancy (known or suspected) or abnormal CSF (raised protein concentration or cell count). A prospective study of the effect of doctordependent variables on the false-negative rates of CSF cytology in cases of known leptomeningeal carcinomatosis demonstrates that false-negative results correlate significantly with small CSF volume, delayed processing, sampling fewer than two times (all P < 0.001), and not obtaining CSF from a site of symptomatic or radiologically demonstrated disease (P 1⁄4 0.02). This study showed that as the amount of CSF sent for analysis increases from 3.5 ml to 7 ml to 10.5 ml, false-negative rates fall from 32% to 10% to 3%. It also showed that a 48-hour delay in processing samples is associated with a false-negative rate of 38%. With this in mind, we audited requests for cytological examination of CSF received by the neuropathology department at the Royal Preston Hospital. This is a medium-sized District General Hospital in the northwest of England with sub-regional neurology and neurosurgery departments. For each sample details of the following information was recorded: department of origin; clinical details provided; amount of CSF sent; cytological findings. Clinical details were divided into four categories: definite indication (e.g. MRI/CT suggestive of malignancy, history of malignancy with CNS signs, known CNS malignancy, raised CSF protein or cells); indication implied (history of malignancy without CNS signs, CNS signs in immunocompromised patient, malignancy, paraneoplastic syndrome); not indicated (e.g. weakness, sensory changes, bacterial or viral infection, demyelination, confusion, headache, ataxia, etc.); illegible or no details given. Our initial audit, undertaken in May 2002, reviewed 154 samples received over the preceding 6 months. Only 6% samples were accompanied by clinical details suggesting a definite or implied indication for CSF cytology. Similarly only 6% samples were ‡10 ml. The average volume of CSF sent was 1.71 ml. Only 2% samples were diagnostic or suspicious of malignancy. These results were presented at an audit meeting within the Department of Neurology. Further to this meeting it was agreed that CSF should not be sent for cytological examination unless previous history, examination or investigations were suggestive of malignancy or fungal infection. It was also recommended that as much CSF as possible should be sent, preferably ‡10 ml. These recommendations were incorporated within departmental publications, in particular the introductory guidelines given to new junior doctors. As this is a fairly large volume of CSF, doctors are reminded that the recommendation is valid for adults only, and that consideration must be given to amounts required for other important studies. A re-audit, reviewing the 12 months from May 2002 to April 2003 was undertaken in May 2003. The most striking effect of the recommendations was a 52% reduction in the total number of requests for CSF cytology. There had been a 69% reduction in requests from our department. The percentage of samples with definite or implied indications had risen to 54%. Although the percentage of samples ‡10 ml had not changed significantly (8%), the average sample size had risen to 3.26 ml. On this occasion 7% of the samples were diagnostic or suspicious of malignancy. This percentage is consistent with that seen in published series. We have demonstrated that recommendations made following audit can reduce inappropriate Correspondence: Mark W. Weatherall, Royal Preston Hospital, Department of Neurology, Preston, Lancashire, UK. E-mail: mark.weatherall@doctors.org. uk