Evaluation of Sysmex UF-1000i for use in cerebrospinal fluid analysis

BACKGROUND: Caution is of paramount importance in the interpretation of flow cytometric white blood cell counts in specimens with a high lymphocyte percentage as it is in the interpretation of bacterial counts in hemorrhagic and ventricular drainage CSF specimens. Recently, flow cytometry using a semiconductor laser along with forward and sideward scatter detection and also a dedicated bacterial channel has been developed (Sysmex UF-1000i). We explored the possible applications of this novel approach in the differential diagnosis of meningitis. METHODS: Flow cytometry, microscopy and biochemical data of 161 CSF samples were analyzed. Microbiological analysis was performed in 53 suspected cases of meningitis. RESULTS: Good agreement for leukocytes was obtained between UF-1000i (rho=0.614) and UF-100 (rho=0.582) and microscopy and between both flow cytometers (rho=0.734). Lymphocytes were correctly classified as WBC by UF-1000i. Bacterial count on UF-1000i showed to be reliable in hemorrhagic samples and in samples collected by ventricular drainage for which interference by blood platelets and cell debris forms a known caveat on UF-100. Bacterial background signal in sterile CSF samples was absent on UF-1000i. One case of Cryptococcus neoformans meningitis, missed by UF-100 was properly detected by UF-1000i. CONCLUSION: Sysmex UF-1000i CSF flow cytometer offers the clinician an improved aid in directing the differential diagnosis of meningitis towards viral, bacterial or fungal causes.